An t im icr obia l Pe pt ide s: Th e ir Role in I n n a t e I m m u n e
Sy st e m a n d Usa ge in Fu t u r e D r u g D e v e lopm e n t
*
1Trist ia Rinanda
1
Depart m ent of Microbiology, Facult y of Medicine, Syiah Kuala Universit y, Darussalam ,
Banda Aceh 23111, I ndonesia;
* Corresponding Aut hor
: t rist ia.rinanda@unsyiah.ac.id
Abst r a ct
Ant im icr obial pept ides nat urally play a role in t he innat e im m une sy st em of any liv ing organism s. These sm all m olecules are k now n as " ancient w eapon" and also recognized as nat ural an t ibiot ics. Ant im icr obial pept ides hav e dist inct charact erist ics including t heir unique st r uct ures w hich are st rongly cor relat ed t o t heir an t im icrobial act iv it ies. Recent ly t he dev elopm ent of ant im icr obial pept ides as fut ure ant im icrobial agent s has becom e a m aj or issue in t he pharm aceut ical business. This art icle w ill discuss t he nat ural r ole of ant im icrobial pept ides in host defence sy st em and t he relat ionship of t heir st ru ct ure w it h ant im icrobial act iv it y . Th is art icle w ill also discuss t he challenge in dev eloping ant im icrobial pept ides as fut ure ant im icr obial agent s.
Ke y w or ds: ant im icrobial pept ide, drug dev elopm ent , ant im icrobial act iv it y
I n t r od u ct ion
Over t he last few decades, t he world has been in war wit h m icrobial resistance. This phenom enon has caused several problem s in healt h sect or such as prolonged illnesses and increased m ort alit y of pat ients which result in increased t reatm ent cost. The progress of ant im icrobial resist ance is a part of nat ural process in m icroorganism s, and is accelerated by external select ive pressures exert ed by use and m isuse of ant im icrobial agents in hum ans and anim als. On t he ot her hand, t he developm ent of new ant im icrobial agent s t o replace t he exist ing ineffect ive drugs has showed a decelerated progress(WHO, 2014) .
To overcom e the m icrobial resistance, WHO has encouraged the global com m it m ents t o im prove the finding and develop t he new ant im icrobial agent s from any available sources(WHO 2015) . One of t he prom ising new ant im icrobial agents is ant im icrobial pept ides. Ant im icrobial pept ides play an im port ant role in innat e im m unit y of host defence syst em and are defined as “ ancient weapon” . These m olecules m ost ly expressed in invert ebrat es since t hese organism do not produce specific ant ibodies and com pletely rely on t he innat e im m unit y m echanism ( Cho et al, 1998) .To date, m any st udies have explored t he ant im icrobial pept ides including t heir st ruct ures and m odes of act ions which init iated t he developm ent of AMPs in pharm aceut ical indust ries. This paper will bring t he closer look on AMPs, including t heir nat ural behaviour in innate im m une syst em , their unique st ruct ures and ant im icrobial act ivit ies, t heir prom ising feat ures as ant im icrobial agent s and also challenges in fut ure drug developm ent .
AMPs Act ion in I n n a t e I m m u n ity
The init ial cont act of host and any fast idious m icroorganism usually occurs at t he inner or out er surface of t he body and t hat is where t he infect ion prim arily t akes place.I nnat e im m unit y as t he first line of defence acts wit hin a few hours aft er m icrobial exposure t o a m ucosal surface (Marshall, 2003) .I n bot h plant s and anim als, innat e im m unity is t riggered by t he recognit ion of m icrobe-associat ed m olecular pat terns ( or pathogen- icrobe-associated m olecular pat t erns) by t he patt ern recognit ion recept ors. This recognit ion is t hen followed by the local and system ic responses which are very specific t o different t axa. However t he expression of AMPs after infect ions of m icrobes in innate im m unit y is conserved in all t ypes of organism s ( Zasloff, 2002) . Several effects of AMPs are enhancing phagocyt osis, st im ulat ing the prostaglandin release, neut ralizing the sept ic effect of Lipopolysaccharides ( LPS) and prom ot ing recruitm ent and accum ulat ion of various im m une cells at inflam m at ory sit es ( Sánchez et al, 2013). Ot her effect s of AMPs which nam ely as im m unom odulat oryeffects are inducing t he proliferat ion of fibroblast and epithelial cells in t he airway ( airway rem odelling process), inducing t he phenot ypic and funct ional changes in dendrit ic cells and inhibit ing pro- inflam m atory cyt okines and m olecules, such as TNF-α, nitrite- oxide and t issue fact ors ( Guaní- Guerra et al., 2010) .
Ant im icrobial pept ides in anim als are produced by the epit helial cells due t o t he direct cont act with t he environm ent and can be secreted t o the circulat ion ( through blood st ream or lym phoid drainage). This circulat ion delivers t he AMPs t o t he site of infect ions. I n plants, AMPs are probably not circulated,
but they areexpressed const itut ively in specific sensit ive organs or induced by local and syst em ic m icrobe infect ions ( Sels et al., 2008) .Recent st udies have ident ified a large num ber of AMP- like genes in eukaryot ic organism s. These findings em phasize t he im portance of AMPs in eukaryot ic im m une system , part icularly in plant s that do not have acquired im m unit y ( Silverstein et al. 2007) .
There are several AMPs produced in m am m alian cells, such as defensins and cat helicidins. Most of AMPs in intest ines are produced by panet h cells, including alpha and bet a defensins. The expression of certain pept ides encoded by AMP genes influences t he t issue’s suscept ibilit y t o infect ions from several pathogenic bact eria. Cathelicidins protect s m ice skin from st rept ococcus and pulm onary t issue from
Pseudom onas aeruginosa. These exam ples indicate that t he effect s of AMPs in m am m als are t issue-specific and st rongly correlated to t he expression pattern of AMP genes (Marót i et al., 2011) .
St r u ct u re - An t im icr ob ia l Act iv it y Rela t ionsh ip of AMPs
Classically, all pept ides can adopt t he m em brane-bound am phipathic conform at ion alt hough their lengt hs, am ino acids com posit ion and secondary st ruct ures are ext rem ely varied. Recent studies dem onst rat e that AMPs have m ult iple m echanism s of ant im icrobial act ivit ies. I n order to design t he rat ional ant im icrobial agents, it is very im port ant t o com prehend t he st ruct ure- act ivit y relat ionship of AMPs ( Nguyen et al., 2011) .
There are two com m on physiochem ical features of AMPs; a cat ionic charge and a subst ant ial proport ion of hydrophobic am ino acids. Cat ionic charge prom otes select ivit y for negat ively charged m icrobial cyt oplasm ic m em branes over zwit terionic m am m alian m em branes. Hydrophobic features facilit at e t he int eract ion with fatt y acyl chain ( Lohner & Prenner, 1999) . There are also anionic AMPs m ore likely t o dem onst rat e ot her biological act ivit ies and m ore t oxic t o m am m alian cells (Harris et al., 2009) .
The m ost com m on ant im icrobial act ivit y of AMPs is t he disrupt ion of bacterial cyt oplasm ic m em branes. The event st art s when bacterial cyt oplasm ic m em branes com e in cont act wit h AMPs t hrough absorpt ion process. This init ial event is followed by several t heoret ical disrupt ion m echanism s such as pore form ing, carpet m odel, barrel st ave, elect roporat ion, non- lyt ic m em brane depolarizat ion, disordered t oroidal pore, m em brane thinning/ t hickening, charged lipid clustering, non- bilayer int erm ediate, anion carrier and oxidized lipid t arget ing ( Giuliani et al., 2007; Nguyen et al., 2011) . To date, there are other cellular target ing m echanism s t hat have been ident ified, such as disrupt ion of DNA and prot ein synt hesis, protein folding, enzym at ic react ions and cell wall synt hesis ( Nikolas, 2009).There are three major structures of AMPs namely α- helical AMPs, β- sheet AMPs and extended AMPs. The relat ionship between each st ructure and the ant im icrobial act ivit y will be discussed below:
α- helical AMPs
α- helical AMPs form a m em brane-bound α helices containing large hydrophobic surfaces which are correlat ed t o cyt otoxic effects t o m am m alian cells. AMPs wit h low t oxicit y can be form ed in a membranous environment to induce the proper folding. Most of α- helical AMPs wit h low cyt ot oxicit y often have proline or glycine induced kink in the middle of α-helix form at ion. The pept ides can lie parallel t o t he m em brane plane during t he init ial int eract ion wit h t he charged side facing out ward t oward t he phospholipid head groups and t he hydrophobic sites inserted int o t he acyl t ail core, which represent t he am phipat icit y along t he axis of α-helix. The α- helix t ail is a very im port ant st ruct ure which influences t he dept h of insert ion t o m em brane, t hus also determ ining t he ant im icrobial act ivit y ( Nguyen et al. 2011) . Am phipat hic helical conform at ion influences t he ant im icrobial act ivit y. I n the st udy of m againin, t he replacem ent of several am ino acids in AMPs by t heir D- isom er result ing in t he loss in m icrobe- killing act ivit ies ( Epand & Vogel, 1999) .
During the insertion, the AMPs undergo partial unfolding; therefore the α- helix st ruct ure is not always m aintained. There are a num ber of polar or charged am ino acids in the hydrophobic face of AMPs which pull t he lipid head groups int o t he m em brane int erior, result ing in pore form at ion( Nguyen et al., 2011) . The pore form at ion is a cooperat ive process; t herefore, t he m em brane integrit y is t em porarily rupt ured. Mem brane- bound pept ide threshold level plays a crit ical role in t he m icrobial m em brane disrupt ion. Once it is reached, the m em brane will solubilize in detergent - like m anner( Nicolas, 2009) .
Another membrane disruption mechanism of α- helix AMPs is lipid segregat ion. The ionic lipid in bact erial m em branes will form aggregat ion thus result ing in slow leakage of int racellular com ponents and m em brane depolarizat ion( Flem ing et al., 2008) . The release of ROS product s during phagocyt osis will increase the lipid oxidation. Oxidized lipids become the target of α-helical AMPs, such as t em porinB and L, in order t o int ercalat em ore efficient ly t o t he m em branes( Mat t ila et al., 2008) . I n
certain AMPs, m em brane disrupt ion m echanism is pH- dependent ( Epand & Epand, 2009) . Despit e the membrane perturbation, several α- helical AMPs obt ain t he int racellular killing m echanism . A st udy in AMPs Buforin I I shows that t he AMPs accum ulate in the cyt oplasm after t ranslocat ion and interact wit h t he nucleic acids ( Lan et al., 2010) .
β- sheet AMPs
The β-sheet AMPs include several β- hairpin pept ides in addit ion to t he defensin m ini- prot eins. This structure forms oligomerictransmembrane β-barrel in anionic membranes and β-sheet aggregates in cholesterol- cont aining m em branes. Many of t hese AMPs kill m icrobes by m em brane t oroidal pore forming. Cathepsin, one of β-sheet AMPs, is able t o disturb t he DNA-protein interaction, whereas β -hairpin AMP bovine lactoferin act s synergically wit h ot her AMPs in affect ing t ransm em brane potent ial and prot on-m ot ive force which results in inhibit ion of ATP- dependent m ult i- drug efflux pum p. Bovine lact oferininhibites DNA and prot ein synthesis during it s presence in cyt oplasm aft er t ranslocat ion process. I nhibit ion of cell wall synthesis in St aphylococcus is conducted by AMP hum an defensins( Nguyen et al., 2011).
The β sheet and β barrel protein conformation is often stabilized by disulphide bonds between Cystein residues (Cézard et al, 2011) . This covalent bonds do not alt er t he ant im icrobial act ivit y. The rearrangem ent of Cystein residues in AMP chain does not abolish t he ant im icrobial act ivit y nor t he secondary st ruct ures. Alt hough ant im icrobial act ivit y m ay be unaffected, t he analogue of AMPs wit hout disulphide linkage shows t he lower chem otactic act ivit y ( Nguyen et al., 2011) .
A study on garam icin S shows t hat t he pept ides wit h high am phipat hicit y perform high haem olyt ic act ivit y but low ant im icrobial act ivit y. Low- am phipat hicit y pept ides, at som e point , can pass t he t hreshold and perform t he higher ant im icrobial act ivit y. This study suggests t hat t he ionic int eract ion bet ween posit ive charges on pept ides and negative charges on m icrobial m em branes is very fundam ental t o ant im icrobial act ivit y ( Midura- Noeaczek & Markowska, 2014) .
Ext ended AMPs
Ext ended AMPs do not fold into regular secondary st ruct ures. The sequence is rich by one or t wo am ino acids, such as Arginin, Prolin or Trypt ophan ( Epand & Vogel, 1999) . I n insect -derived Prolin- rich AMPs, drosocins and apidaecins, t he ant im icrobial act ivit y can be perform ed by penet rat ion t o m em branes and interact ion wit h t he int racellular propert ies, result ing in inhibit ion of DnaK ATPase act ivit y and Chaperone assisted protein folding ( Brogden & Brogden, 2011) . Ot her extended AMPs act by st opping t he replicat ion fork, t hus prevent ing recom binat ion and DNA repair ( Nguyen et al., 2011).
The Proline and Arginin- rich com posit ion in porcine PR- 39 plays an im portant role in bacteria killing m echanism t hrough its interact ion wit h cyt oplasm ic prot eins. I ndolicins is an AMP analogue which successfully shows it s ant im icrobial act ivit ies such as act ivat ing t he phospholipaseA which hydrolyses t he anionic m em branes, disrupt ing m em branes t hrough lipid segregat ion of oxidized phospholipids, act ing as sm all anion carriers across t he m em branes and int erfering DNA binding Enzym es in
Escherichia coli ( Marchand et al., 2006).
Ch a lle ng es in Fu t ur e D ru g De v elop m e n t
AMPs have a num ber of desirable feat ures as novel ant im icrobial agent s or as a com plem ent to convent ional ant ibiot ic t herapy ( Giuliani et al., 2007). They are ubiquit ous in nature, t ypically show a rapid and broad spect rum ant im icrobial act ivit y against pathogenic bacteria and fungi. They are also able to dest roy enveloped viruses, parasit es and even cancerous cells ( Nguyen et al., 2011). I n accordance wit h t heirnat ural roles in innate im m unit y, AMPs also exhibit im m unom odulat ory effect s ( Guaní- Guerra et al., 2010) . These features are the underlying idea for t he developm ent of AMPs as ant im icrobial agents. Anot her interest ing feat ure of AMPs are t heir abilit y t o reduce biofilm and persister cells (Chen et al., 2011) , t hus expanding t he use of AMPs as the ant im icrobial coat ing agent s for m edical devices (Onaizi & Leong, 2011).
The m ost im port ant feat ure of AMPs, especially eukaryot ic AMPs, as fut ure ant im icrobial agents is t he low suscept ibilit y t o m icrobial resist ance due to gene m utat ion. Many eukaryot ic AMPs perform m ore t han one killing m echanism . They can act on t he m icrobial m em branes and other generalized targets whereas t he convent ional ant ibiot ics act only in specific protein t arget s (Peschel & Sahl, 2006) . A st udy by Fedders et al reveals that Ci- MAM- A24, t he synt het ic AMP deriving from the im m une cells of a m arine invertebrate, Cionaintest inalis, shows significant ant im icrobial act ivit y against m ult idrug resist ant bact eria and pat hogenic anaerobe bacteria in hum an (Fedders et al., 2010) . The bact erial resist ance m echanism s t o AMPs have been ident ified and reported, but t he num ber is considerably
lower than t he resist ance t o convent ional ant ibiot ics ( Peschel & Sahl, 2006) .Despit e t heir desirable feat ures, AMPs have several short com ings which can lim it t heir characterist ics in clinical applicat ions, such as haem olyt ic act ivit y, rapid t urnover in t he hum an body, reduced act ivit y due t o salt sensit ivit y, high cost of product ion and broad spect rum ant im icrobial act ivit y ( Aoki & Ueda, 2013).
Haem olit ic act ivit y
The haem olyt ic act ivit y can be m easured by a therapeut ic index, which represent s the rat io of ant im icrobial act ivit y t o haem olyt ic act ivit y. The high t herapeut ic index of AMPs is essent ial for host cells t o avoid t he haem olysis. I n m ost AMPs, t heir haem olyt ic act ivit y is equal t o ant im icrobial act ivit y ( Lee et al., 2011) . The increase of hydrophobicit y leads t o a m ore effect ive non- specific interact ion wit h m em branes of both of bacteria and eryt hrocyt es ( Findlay et al., 2012). Am phiphilicit y also cont ributes t o higher haem olyt ic act ivit y. That is why changes in hydrophobicit y and am phiphilicit y can be considered in order t o m inim ize t he undesirable effect s (Aoki & Ueda, 2013). Haem olyt ic act ivit y can be avoided by using non- haem olyt ic seeds of AMPs ( Aoki & Ueda 2013), such as Lum bricin- 1, annelids-derived AMPs (Cho et al. 1998). A st udy by St randberg et al concludes that t he haem olyt ic act ivit y can be reduced while m aintaining t he ant im icrobial act ivit y by conduct ing C- term inal deam idat ion of AMPs ( St randberg et al., 2007) .
Rapid turnover in t he hum an body
Rapid t urnover in t he hum an body is correlated with t he protease act ivit y which rapidly degrades t he AMPs. The stabilit y against protease is very essent ial for AMPs in clinical use. There are several st rategies t o overcom e this stabilit y issue nam ely D- isom erizat ion, incorporat ion of chem ical com pounds, cyclizat ion and pept idom im et ic. D- isom erizat ion t urns t o be t he best st rat egy t o obt ain t he best proteolyt ic stabilit y ( Aoki & Ueda, 2013), even though it is not cost -effect ive and cannot be used in certain AMPs (chiralit y- dependent AMPs) . End capping shows that C- term inal deam idat ion provides lower proteolyt ic st abilit y and higher ant im icrobial act ivit y m eanwhile t he N- term inal deam idat ion exerts higher stabilit y and lower m icrobes killing abilit y. Pept ide cyclizat ion is able t o m aintain bot h prot eolyt ic stabilit y and ant im icrobial act ivit y ( Nguyen et al., 2010) . I ncorporat ion of chem ical com pounds obt ains steric occlusion which covers t he prot ease act ive sit e on pept ide sequence, t hus result ing in resistance t o protease degradat ion. ( Mat suzaki 2009) .The const ruct ion of pept ide-m im et ic, t he polym er that m im ics t he com plex st ruct ure of AMPs, shows an im provem ent in protease stabilit y.The polym ers do not have protease act ive sit e so they exhibit high st abilit y against protease ( Berhanu et al., 2012).
Reduced act ivit y due t o salt sensit ivit y
I n order t o form secondary st ructures, AMPs need elect rostat ic int eract ion wit h m icrobial m em branes. This st age is salt - sensit ive. The hum an body fluids cont ain high salt concent rat ion which can deact ivat e t he AMPs. Designing the salt - insensit ive AMPs will produce the m ore st able secondary st ruct ures. The use of helix- capping m ot ifs bot h in C- term inal and N- term inal of t he pept ides m aintains the ant im icrobial act ivit y and obt ains m ore st able helical AMPs in high concent rat ion of NaCl com pared t o unm odified AMPs( Yu et al., 2011) .
High cost of product ion
One of t he m aj or concerns in pharm aceut ical indust ries in developing AMPs as novel ant im icrobial agents is t he high product ion cost. I t is higher than product ion cost of convent ional ant ibiot ics. Anot her problem com es from t he difficult ies t o produce het erologous AMPs in prokaryot ic system since t he AMPs are t oxic to prokaryot ic cells. The st rategies to abolish t he t oxicit y in the host cells and t o increase t he am ount of AMPs are very essent ial t o reduce t he cost of product ion ( Aoki & Ueda, 2013) . Fusion expression using solubilit y- enhancing carriers obtains t he high yield of AMPs. The use of t hioredoxin( Bogom olovas et al., 2009) and Sm all Ubiquit ous- related Modifier (SUMO) has produced non- t oxic AMPs ( Aoki & Ueda, 2013) .
Broad spect rum ant im icrobial act ivit y
The hum an body has a sym biot ic relat ionship wit h m icrobiota. The developm ent of AMPs as ant im icrobial agent s m ust consider t he presence of this im portant m ucosal surface com ponent so t hat t he AMPs can kills t he pat hogenic m icrobes while sust aining the com m ensal m icrobiota( Aoki & Ueda, 2013) . Therefore, it is very essent ial t o const ruct AMPs which develop select ivit y only t o pat hogenic m icrobes. Specifically t argeted ant im icrobial pept ide ( STAMP) technology has been int roduced and generated a prom ising approach. STAMP t echnology is t he const ruct ion of fusion pept ide consist ing of t wo funct ional independent dom ains ( target ing dom ain and killing dom ain) using short flexible linker. The t arget ing dom ain is responsible for the interact ion wit h m em brane hydrophobicit y charge, pherom one recept ors, cell wall att ributes and ot her virulence fact ors which are t he specific
det erm inant s on pathogen surface ( Eckert et al., 2006) . Select ive killing m echanism can be accom plished by using environm ent sensing. This m et hod is based on t he environm ental changes due t o overgrowt h and m etabolic act ivit ies. One of t he environm ent al indicators already studied is pH. The acid-act ivat ed AMPs can kill t he pat hogenic m icrobes such as Candida albicansin a low-pH environm ent ( Aoki & Ueda, 2013) . Anot her m ethod to establish the select ivit y is using protease-act ivated AMPs. This m ethod develops protease as the target since t he pathogenic m icrobes possess t he specific proteases wit h subst rat e specificit y charact erist ic ( Aoki & Ueda, 2013).
Con clusion
Ant im icrobial pept ides have caught t he at tent ion of the research world and pharm aceut ical business. As part of innate im m unit y, t hese m olecules show interest ing feat ures related t o t he exterm inat ion of pathogenic m icrobes and possession of t he im m unom odulatory effect s. AMP feat ures are st rongly correlated to their unique structures, such as α-helical, β- sheet and extended AMPs. Underst anding t he way the st ructures influence t he act ivit y is very im port ant t o facilit ate t he rat ional design of novel ant im icrobial agent s. Despit e t heir desirable feat ures, AMPs exhibit lim it at ion related t o their clinical applicat ion such as haem olyt ic act ivit y, rapid turnover in t he hum an body, salt sensit ivit y, high cost product ion, and broad spect rum ant im icrobial act ivit y harm ful t o com m ensal m icrobiot a. These problem s are challenges that need t o be overcom e. To date, t here are a large num ber of st udies conduct ed t o m odify t he AMPs. These st udies share the sam e object ive t hat is t o develop t he AMPs as novel ant im icrobial agent s by elim inat ing the lim it at ion and im proving t he desirable feat ures.
Re fe re n ces
Aoki, W. & Ueda, M., 2013. Characterizat ion of Ant im icrobial Pept ides t oward t he Developm ent of Novel Ant ibiot ics. Pharm aceut icals ( Basel, Switzerland), 6( 8) , pp.1055–81. Available at : ht t p: / / www.pubm edcent ral.nih.gov/ art iclerender.fcgi?art id= 3817730&t ool= pm cent rez&rendert yp e= abst ract .
Berhanu, W.M. et al., 2012. Sim ilarit y analysis, synt hesis, and bioassay of ant ibact erial cyclic pept idom im et ics. Beilstein Journal of Organic Chem istry, 8, pp.1146–1160.
Bogom olovas, J. et al., 2009. Screening of fusion part ners for high yield expression and purificat ion of bioact ive viscot oxins. Protein expression and purificat ion, 64( 1) , pp.16–23.
Brogden, N.K. & Brogden, K. a., 2011. Will new generat ions of m odified ant im icrobial pept ides im prove t heir potent ial as pharm aceut icals? I nt ernat ional Journal of Ant im icrobial Agent s, 38( 3) , pp.217–225. Available at : htt p: / / dx.doi.org/ 10.1016/ j .ij ant im icag.2011.05.004.
Cézard, C. et al., 2011. Ant ibact erial Pept ides : A Review. Form atex, pp.926–937.
Chen, X. et al., 2011. Cont rol of bacterial persist er cells by Trp/ Arg-cont aining ant im icrobial pept ides.
Applied and Environm ent al Microbiology, 77( 14), pp.4878–4885.
Cho, J.H. et al., 1998. Lum bricin I , a novel proline- rich ant im icrobial pept ide from t he eart hworm : puri ¢ cat ion , cDNA cloning and m olecular characterizat ion. Science, 1408, pp.67–76.
Eckert, R. et al., 2006. Adding Select ivit y t o Ant im icrobial Pept ides : Rational Design of a Multidomain Pept ide against Pseudom onas spp . Adding Select ivit y t o Ant im icrobial Pept ides : Rational Design of a Mult idom ain Pept ide against Pseudom onas spp . Societ y, 50( 4), pp.1480–1488.
Epand, R.M. & Epand, R.F., 2009. Lipid dom ains in bacterial m em branes and t he act ion of ant im icrobial agents. Biochim ica et Biophysica Acta - Biom em branes, 1788( 1) , pp.289–294. Available at : htt p: / / dx.doi.org/ 10.1016/ j.bbam em .2008.08.023.
Epand, R.M. & Vogel, H.J., 1999. Diversit y of ant im icrobial pept ides and their m echanism s of act ion.
Biochim ica et Biophysica Acta - Biom em branes, 1462( 1- 2) , pp.11–28.
Fedders, H., Podschun, R. & Leippe, M., 2010. The ant im icrobial pept ide Ci- MAM- A24 is highly act ive against m ult idrug- resist ant and anaerobic bact eria pat hogenic for hum ans. I nternat ional Journal of Ant im icrobial Agents, 36( 3) , pp.264–266.
Findlay, B., Zhanel, G.G. & Schweizer, F., 2012. I nvest igat ing t he ant im icrobial pept ide “ window of act ivit y” using cat ionic lipopept ides wit h hydrocarbon and fluorinat ed t ails. I nt ernat ional Journal of Ant im icrobial Agents, 40( 1) , pp.36–42.
Flem ing, E. et al., 2008. Effect of lipid com posit ion on buforin I I st ruct ure and m em brane ent ry.
Proteins: St ructure, Funct ion, and Bioinform at ics, 73(2) , pp.480–491.
Giuliani, A., Pirri, G. & Nicolett o, S.F., 2007. Ant im icrobial pept ides: an overview of a prom ising class of t herapeut ics,
Guaní- Guerra, E. et al., 2010. Ant im icrobial pept ides: General overview and clinical im plicat ions in hum an health and disease. Clinical I m m unology, 135( 1) , pp.1–11. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.clim .2009.12.004.
Haine, E.R. et al., 2008. Ant im icrobial defence and persist ent I nfect ion in I nsect s. Science, 322( Novem ber) , pp.1257–1259.
Harris, F., Dennison, S.R. & Phoenix, D. a, 2009. Anionic ant im icrobial pept ides from eukaryot ic organism s. Current protein & pept ide science, 10(6) , pp.585–606.
Janeway, 2005. I m m unobiology: The I m m une System in Health and Diseases 6th ed., New York: Garland Science.
Lan, Y. et al., 2010. St ruct ural cont ribut ions t o t he int racellular t arget ing st rat egies of ant im icrobial pept ides. Biochim ica et Biophysica Act a - Biom em branes, 1798(10) , pp.1934–1943. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.bbam em .2010.07.003.
Lee, S.H. et al., 2011. De novo generat ion of short ant im icrobial pept ides with sim ple am ino acid com posit ion. Regulat ory Pept ides, 166(1- 3) , pp.36–41. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.regpep.2010.08.010.
Lohner, K. & Prenner, E.J., 1999. Different ial scanning calorim et ry and X- ray diffract ion studies of t he specificit y of t he int eract ion of ant im icrobial pept ides wit h m em brane- m im et ic system s.
Biochim ica et biophysica act a, 1462( 1- 2), pp.141–156.
Marchand, C. et al., 2006. Covalent binding of t he nat ural ant im icrobial pept ide indolicidin to DNA abasic sit es. Nucleic Acids Research, 34( 18) , pp.5157–5165.
Marót i Gergely, G. et al., 2011. Nat ural roles of ant im icrobial pept ides in m icrobes, plants and anim als. Research in Microbiology, 162( 4) , pp.363–374.
Marshall, S.H., 2003. Full Text - Ant im icrobial pept ides A nat ural alternat ive t o chem ical ant ibiot ics and a pot ent ial for applied biot echnology. , 6( 2).
Matsuzaki, K., 2009. Cont rol of cell select ivit y of ant im icrobial pept ides. Biochim ica et Biophysica Acta - Biom em branes, 1788( 8) , pp.1687–1692. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.bbam em .2008.09.013.
Mat t ila, J.-P., Sabat ini, K. & Kinnunen, P.K.J., 2008. Oxidized phospholipids as potent ial m olecular t argets for ant im icrobial pept ides. Biochim ica et biophysica act a, 1778( 10) , pp.2041–2050. Midura- Noeaczek, K. & Markowska, A., 2014. Ant im icrobial pept ides and t heir analogs: Searching for
new potent ial t heurapeut ics. Perspect ive in Medicinal Chem ist ry, 6, pp.73–80.
Nguyen, L.T. et al., 2010. Serum stabilit ies of short t rypt ophan- and arginine- rich ant im icrobial pept ide analogs. PLoS ONE, 5( 9) , pp.1–8.
Nguyen, L.T., Haney, E.F. & Vogel, H.J., 2011. The expanding scope of ant im icrobial pept ide st ruct ures and t heir m odes of act ion. Trends in Biotechnology, 29( 9) , pp.464–472. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.t ibtech.2011.05.001.
Nicolas, P., 2009. Mult ifunct ional host defense pept ides: I nt racellular- t arget ing ant im icrobial pept ides.
FEBS Journal, 276( 22) , pp.6483–6496.
Nikolas P, 2009. Mult ifunct ional host defense pept ide: I nt racellular t arget ing ant im icrobial pept ides.
FEBS, 276, pp.6483–6496.
Onaizi, S. a. & Leong, S.S.J., 2011. Tet hering ant im icrobial pept ides: Current stat us and potent ial challenges. Biot echnology Advances, 29( 1) , pp.67–74. Available at : ht t p: / / dx.doi.org/ 10.1016/ j.biotechadv.2010.08.012.
Peschel, A. & Sahl, H.- G., 2006. The co-evolut ion of host cat ionic ant im icrobial pept ides and m icrobial resist ance. Nature Reviews Microbiology, 4, pp.529–536.
Ryu, J.-H. et al., 2006. An essent ial com plem entary role of NF- kappaB pathway to m icrobicidal oxidants in Drosophila gut im m unit y. The EMBO j ournal, 25( 15) , pp.3693–3701.
Sánchez, M.L. et al., 2013. Nat ural Ant im icrobial Pept ides : Pleiotropic Molecules in Host Defense.
CellBio, 2( Decem ber), pp.200–210.
Schibli, D.J., Hwang, P.M. & Vogel, H.J., 1999. St ruct ure of t he ant im icrobial pept ide t rit rpt icin bound t o m icelles: A dist inct m em brane- bound pept ide fold. Biochem ist ry, 38( 51), pp.16749–16755. Sels, 2008. Plant pat hogenesis- related ( PR) prot eins: a focus on PR pept ides. Plant . Physiol. Biochem,
46, pp.941–950.
Silverstein, K. a T. et al., 2007. Sm all cyst eine- rich pept ides resem bling ant im icrobial pept ides have been under-predicted in plants. Plant Journal, 51(2) , pp.262–280.
St randberg, E. et al., 2007. I nfluence of C-t erm inal am idat ion on t he ant im icrobial and hem olyt ic act ivit ies of cat ionic α- helical pept ides. Pure and Applied Chem ist ry, 79( 4), pp.717–728.
Tzou, P. et al., 2000. Tissue-specific inducible expression of ant im icrobial pept ide genes in Drosophila surface epithelia. I m m unit y, 13( 5), pp.737–748.
WHO, 2014. ANTI MI CROBI AL RESI STANCE Global Report on Surveillance 2014. World Healt h Organizat ion.
WHO, 2015. Outcom e Statem ent 1. I n WHO, pp. 26–27. Available at : ht t p: / / www.who.int / drugresistance/ event s/ brazilm eet ingm arch2015/ en/ .
Yu, H.Y. et al., 2011. Easy st rategy t o increase salt resist ance of ant im icrobial pept ides. Ant im icrobial Agents and Chem ot herapy, 55( 10), pp.4918–4921.
Zasloff, 2002. Ant im icrobial Pept ide of Mult icellular Organism s. Nature, 415, pp.389–395.
