title: Roles of the N- and C-terminal sequences in Hsp27 self-association and chaperone activity.
abstract: The small heat shock protein 27 (Hsp27 or HSPB1) is an oligomeric molecular chaperone in vitro that is associated with several neuromuscular, neurological, and neoplastic diseases. Although aspects of Hsp27 biology are increasingly well known, understanding of the structural basis for these involvements or of the functional properties of the protein remains limited. As all 11 human small heat shock proteins (sHsps) possess an α-crystallin domain, their varied functional and physiological characteristics must arise from contributions of their nonconserved sequences. To evaluate the role of two such sequences in Hsp27, we have studied three Hsp27 truncation variants to assess the functional contributions of the nonconserved N- and C-terminal sequences. The N-terminal variants Δ1-14 and Δ1-24 exhibit little chaperone activity, somewhat slower but temperature-dependent subunit exchange kinetics, and temperature-independent self-association with formation of smaller oligomers than wild-type Hsp27. The C-terminal truncation variants exhibit chaperone activity at 40 °C but none at 20 °C, limited subunit exchange, and temperature-independent self-association with an oligomer distribution at 40 °C that is very similar to that of wild-type Hsp27. We conclude that more of the N-terminal sequence than simply the WPDF domain is essential in the formation of larger, native-like oligomers after binding of substrate and/or in binding of Hsp27 to unfolding peptides. On the other hand, the intrinsically flexible C-terminal region drives subunit exchange and thermally-induced unfolding, both of which are essential to chaperone activity at low temperature and are linked to the temperature dependence of Hsp27 self-association.
authors: Department of Biochemistry and Molecular Biology and the Centre for Blood Research, University of British Columbia, Vancouver, BC, Canada.
authors: Barbara
authors: B
authors: Lelj-Garolla
authors: A Grant
authors: AG
authors: Mauk
mesh_terms: D055551:HSP27 Heat-Shock Proteins / Q000737:chemistry* / Q000378:metabolism*; D006360:Heat-Shock Proteins; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D018832:Molecular Chaperones; D008970:Molecular Weight; D011485:Protein Binding; D011489:Protein Denaturation; D055503:Protein Multimerization; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D013696:Temperature; D038201:alpha-Crystallins / Q000737:chemistry / Q000378:metabolism
chemical_list: D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D021122:Protein Subunits; D038201:alpha-Crystallins