Conformational diversity analysis reveals three functional mechanisms in proteins

This paper was published recently in Plos Comp Bio and looks at the conformational diversity (flexibility) of protein structures by comparing solved structures of identical sequences.

The premise of the work is that different crystal structures of the same protein represent instances of the conformational space of the protein. These different instances are identical in amino acid sequence but often differ in other ways they could come from different crystal forms or the protein could have different co-factors bound or have undergone post translational modifications.

The data set used in the paper came from CoDNaS (conformational diversity of the native state) Database URL:http://ufq.unq.edu.ar/codnas.

Only structures solved using X-ray crystallography to a resolution better than 2.5A were used and only proteins for which at least 5 conformers were available (average of 15.53 conformers per protein). Just under 5000 different protein chains made up the set. In order to describe the protein chains the measure used was maximum conformational diversity (the maximum RMSD between any of the conformers of a given protein chain).

The authors describe a relationship between this maximum conformational diversity and the presence absence of intrinsically disordered regions (IDRs). An IDR was defined as a segment of at least 5 contiguous residues with missing electron density (the first and last 20 residues of the chain were not included).

The proteins were divided into three groups.

Rigid

• No IDRS

Partially disordered

• IDRs in at least one conformer
• IDR in the maximum RMSD pair of conformational diversity

Malleable

• IDRs in at least one conformer
• No IDR in the maximum RMSD pair of conformational diversity

Rigid proteins have in general lower conformational diversity than partially disordered than Malleable. The authors describe how these differences are not due to crystallographic conditions, protein length, number of crystal contacts or number of conformers.

The authors then go on to compare other properties based on these three types of protein chains including amino acid composition, loop RMSD and cavities and tunnels.

They summarise their findings with the figure below.