Domain

Domains are formed by combinations of SS, SSS, motifs and connected by loops and turns.

Highly conversed and may be common in most unrelated proteins

They evolve

Can function Independently

Average 100 amino acids 

Single hydrophobic core

TLS Online TPP Program

#Id: 8467

#Unit 1. Molecules and their Interaction Relevant to Biology

polylysine is a random coil at pH values below about 11, where repulsion of positive charges prevents helix formation. At pH 12, where polylysine is a neutral peptide chain, it readily forms an a-helix.

TLS Online TPP Program

#Id: 8468

#Unit 1. Molecules and their Interaction Relevant to Biology

polyGlu is a random coil at pH values above about 5, where repulsion of negative charges prevents helix formation. 

TLS Online TPP Program

#Id: 8469

#Unit 1. Molecules and their Interaction Relevant to Biology

The RHH (L amino acids) α helix, which ideally has ϕ = −57° and ψ = −47°

TLS Online TPP Program

#Id: 8470

#Unit 1. Molecules and their Interaction Relevant to Biology

The two forms of poly(Pro)

all cis (I) or all trans (II) peptide bonds. 

poly(Pro) I as a right-handed helix with 3.3 residues per turn 

poly(Pro) II is a left-handed helix with 3 residues per turn.

TLS Online TPP Program

#Id: 8471

#Unit 1. Molecules and their Interaction Relevant to Biology

poly(Pro) helix are stabilized by water molecule hydrogen bonding

TLS Online TPP Program

#Id: 8472

#Unit 1. Molecules and their Interaction Relevant to Biology

Poly(Gly) chains also adopt secondary conformations. 

In the solid state poly(Gly) has been shown to adopt two regular conformations designated I and II. 

State I has an extended conformation like a β strand whilst state II has three resides per turn and is similar to poly(Pro).