Antimicrobial peptides (part six)

1.Structure of antimicrobial peptides

Most of them are cationic and amphipathic. They contain lots of lysine and arginine residues. The simplest are alpha-helical or beta-sheets.

Both of them are the structural motifs

2. Some review

Alpha helix, beta sheets, and hairpins are examples of secondary structures of proteins.

a) Alpha helix

Antimicrobial peptides-1

Alpha helix  are stabilized by intra-chain hydrogen bonds.

Also, we can see some proteins-keratin and collagen-almost entirely alpha helical in structure.

Globular proteins contain alpha helical and beta sheets regions in addition of region without one of the both.

An alpha helix is formed by making a rope coil in a left handed direction.

Into proteins, the rope is represented by the N-C-C-N-C-C-N-…backbone of the polypeptide chain.

We find also beta sheets.

b) Beta sheets

There are two categories of beta sheets.

One is called parallel :

Antimicrobial peptides-2

We can see the chains are stackable.

The second is called anti-parallel:

Antimicrobial peptides-3

Here, on contrary, the two chains are anti parallel.

These anti parallel beta-sheets are more stable than the parallel.

Like the alpha helix, beta-sheets are held by H-bonds.

Also, in secondary structures we find hairpins

c) Hairpins

hairpins are over loop which permit a flexibility and directionality of the chains:

Antimicrobial peptides-4

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