The role of intrinsically disordered regions in the structure and functioning of small heat shock proteins.

Sudnitsyna MV; Mymrikov EV; Seit-Nebi AS; Gusev NB

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Article

Title:	The role of intrinsically disordered regions in the structure and functioning of small heat shock proteins.
Authors:	Sudnitsyna MV; Mymrikov EV; Seit-Nebi AS; Gusev NB
Publication:	Curr Protein Pept Sci. 2012 Feb;13(1):76-85.
PubmedID	22044147
Abstract
Small heat shock proteins (sHsp) form a large ubiquitous family of proteins expressed in all phyla of living organisms. The members of this family have low molecular masses (13-43 kDa) and contain a conservative alpha-crystallin domain. This domain (about 90 residues) consists of several beta-strands forming two beta-sheets packed in immunoglobulinlike manner. The alpha-crystallin domain plays an important role in formation of stable sHsp dimers, which are the building blocks of the large sHsp oligomers. A large N-terminal domain and a short C-terminal extension flank the alpha-crystallin domain. Both the N-terminal domain and the C-terminal extension are flexible, susceptible to proteolysis, prone to posttranslational modifications, and are predominantly intrinsically disordered. Differently oriented N-terminal domains interact with each other, with the core alpha-crystallin domain of the same or neighboring dimers and play important role in formation of large sHsp oligomers. Phosphorylation of certain sites in the N-terminal domain affects the sHsp quaternary structure, the sHsp interaction with target proteins and the sHsp chaperone-like activity. The C-terminal extension often carrying the conservative tripeptide (I/V/L)-X-(I/V/L) is capable of binding to a hydrophobic groove on the surface of the core alpha-crystallin domain of neighboring dimer, thus affecting the plasticity and the overall structure of sHsp oligomers. The Cterminal extension interacts with target proteins and affects their interaction with the alpha-crystallin domain increasing solubility of the complexes formed by sHsp and their targets. Thus, disordered N- and C-terminal sequences play important role in the structure, regulation and functioning of sHsp.