BAHAN KULIAH BIOKIMIA POWER POINT BAGIAN 1 /BIOCHEMISTRY POWER POINT LECTURES PART 1 | Karya Tulis Ilmiah

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Protein Structure

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beta sheets are twisted

• Parallel sheets are less twisted than antiparallel and are always buried.

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The twist is due to chiral (l)- amino acids in the

extended plane.

This chirality gives the twist and distorts

H-bonding.

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Two proteins exhibiting a twisting



sheet

Bovine carboxypeptidase

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Sheet facts

•Repeat distance is 7.0 Å

•R group on the Amino acids alternate up-down-up above and below the plane of the sheet

•2 - 15 amino acids residues long

•2 - 15 strands per sheet

•Ave of 6 strands with a width of 25 Å

•parallel less stable than anti-parallel

•Anti-parallel needs a hairpin turn

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Non-repetitive regions

Turns - coils or loops link regions of secondary structure 50% of structure of globular proteins are not

repeating structures

 bends

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Folding motifs (super secondary

structure)

Certain amino sequences have patterns to their folding.

A.  motif, B.  hairpin C.  motif

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beta-alpha-beta

• parallel beta-strands connected by longer regions containing alpha-helical segments

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Helix-turn-helix

• loop regions connecting alpha-helical segments can have important functions e.g. EF-hand and DNA-binding

• EF hand loop ~ 12 residues

• polar and hydrophobic a.a. conserved positions • Glycine is invariant at the sixth position

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Protein Folds

There is an estimate of about 10000 different folding

patterns in proteins

About half of the proteins fall into a few dozen folding

patterns.

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The  barrel has several types of

structures that have been mimicked in art.

A. rubredoxin

B. Human prealbumin or porins

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Concanavalin A

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Carbonic anhydrase

H

₂

CO

₃ -

_

CO

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Glyceraldehyde-3-phosphate

dehydrogenase

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Zinc fingers

C2H2 zinc finger: It is characterized by the sequence CX2-4C....HX2-4H,

where C = cysteine, H = histidine, X = any amino acid.

C4 zinc finger: Its consensus sequence is CX2CX13CX2CX

14-15CX5CX9CX2C. The first four cysteine residues bind to a zinc ion and

the last four cysteine residues bind to another zinc ion

C6 zinc finger. It has the consensus sequence CX2CX6CX5-6CX2CX6C.

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Summary Chapter 6

• Four levels of protein structure

– Primary