Interactive sequences in the stress protein and molecular chaperone human alpha B crystallin recognize and modulate the assembly of filaments

Molecular chaperones including the small heat shock proteins, alpha B crystallin and sHSP27 participate in the assembly, disassembly, and reorganization of the cytoskeleton during cell development and differentiation. While aB crystallin and sHSP27 stabilize and modulate filament assembly and re-organization, the sequences and structural domains mediating interactions between these proteins and filaments are unknown. It is important to define these interactive domains in order to understand differential interactions between chaperones and stable or unfolding filaments and their function in the cellular stress response. Protein pin arrays identified sequences in human aB crystallin that selectively interacted with native or partially unfolded filament proteins desmin, glial-fibrillary acidic protein, and actin. Circular dichroism spectroscopy determined differences in the structure of these filaments at 23 and 45 degrees C. Seven alpha B crystallin sequences had stronger interactions with desmin and six sequences had stronger interactions with glial-fibrillary acidic protein at 23 degrees C than at 45 degrees C. The alpha B crystallin sequences 33LESDLFPTSTSLSPFYLRPPSFLR56 and (129)DPLTITSSLSSDGV(145) had the strongest interactions with actin at 23 degrees C, while (57)APSWFDTG(64), (111)HGFISREF(118) (111)VNGPRKQVSG(154), and 155PERTIPITREEK165 had the strongest interactions with actin at 45 degrees C. The actin interactive sequences of alpha B crystallin overlapped with previously identified aB crystallin chaperone sequences and were synthesized to evaluate their effect on the assembly and aggregation of actin. Full-length alpha B crystallin and the core domain chaperone sequence (131)LTITSSLSSDGV(143) promoted actin polymerization at 37 degrees C and inhibited depolymerization and aggregation at 50 degrees C. The results support the hypothesis that interactive domains in alpha B crystallin have multiple functions in stabilizing the cytoskeleton and protecting cytosolic proteins from unfolding. (c) 2007 Elsevier Ltd. All rights reserved.