Self-association of a small heat shock protein.
Human Hsp27 oligomerizes in vivo in a phosphorylation-dependent manner that regulates the functional activity of the protein. We have studied the self-association of wild-type Hsp27 by both sedimentation velocity and sedimentation equilibrium analysis and established that the protein forms an equilibrium mixture of monomers/dimers, tetramers, 12-mers and 16-mers (20 mM Tris-HCl (pH 8.4), 100 mM NaCl, 20 degrees C). Corresponding analysis of the S15D/S78D/S82D triple variant, which is believed to mimic the behavior of phosphorylated Hsp27, establishes that this form of the protein forms primarily monomers and dimers but also forms a small fraction of very large oligomers. Variants in which critical N-terminal sequences have been deleted exhibit oligomerization behavior that is intermediate between that of the triple variant and the wild-type protein. On the other hand a C-terminal sequence deletion variant forms larger oligomers than does the wild-type protein, but also exhibits a greater fraction of smaller oligomers. Notably, the presence of an N-terminal His6-tag induces formation of much larger oligomers than observed for any other form of the protein. The results of this work establish that the wild-type protein forms smaller oligomers than previously believed, define the roles played by various structural domains in Hsp27 oligomerization, and provide improved molecular probes with better-defined properties for the design of future experiments.
Lelj-Garolla
Barbara
B
Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada.
Mauk
A Grant
AG
D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016297:Mutagenesis, Site-Directed; D017384:Sequence Deletion; D014461:Ultracentrifugation
D006360:Heat-Shock Proteins