A Mechanism of Subunit Recruitment in Human Small Heat Shock Protein Oligomers
نویسندگان
چکیده
Small heat shock proteins (sHSPs) make up a class of molecular chaperones broadly observed across organisms. Many sHSPs form large oligomers that undergo dynamic subunit exchange that is thought to play a role in chaperone function. Though remarkably heterogeneous, sHSP oligomers share three types of intermolecular interactions that involve all three defined regions of a sHSP: the N-terminal region (NTR), the conserved α-crystallin domain (ACD), and a C-terminal region (CTR). Here we define the structural interactions involved in incorporation of a subunit into a sHSP oligomer. We demonstrate that a minimal ACD dimer of the human sHSP, HSPB5, interacts with an HSPB5 oligomer through two types of interactions: (1) interactions with CTRs in the oligomer and (2) via exchange into and out of the dimer interface composed of two ACDs. Unexpectedly, although dimers are thought to be the fundamental building block for sHSP oligomers, our results clearly indicate that subunit exchange into and out of oligomers occurs via monomers. Using structure-based mutants, we show that incorporation of a subunit into an oligomer is predicated on recruitment of the subunit via its interaction with CTRs on an oligomer. Both the rate and extent of subunit incorporation depend on the accessibility of CTRs within an HSPB5 oligomer. We show that this mechanism also applies to formation of heterooligomeric sHSP species composed of HSPB5 and HSPB6 and is likely general among sHSPs. Finally, our observations highlight the importance of NTRs in the thermodynamic stability of sHSP oligomers.
منابع مشابه
Cloning and Expression of Heat Shock Protein 60kDa Gene from Brucella melitensis as Subunit Vaccine
Brucellosis is caused by the bacterium Brucella and affects various domestic and wild species. GroEL (Heat Shock Protein 60kDa) as one of the major antigens that stimulate the immune system, increases Brucella survival. The aim of the current study was to clone and express GroEL in Escherichia coli in order to design subunit vaccine. Amplifying was performed using specific primers. The full-len...
متن کاملStructural and functional aspects of hetero-oligomers formed by the small heat shock proteins αB-crystallin and HSP27.
BACKGROUND αB-crystallin and HSP27 are mammalian intracellular small heat shock proteins. RESULTS These proteins exchange subunits in a rapid and temperature-dependent manner. CONCLUSION This facile subunit exchange suggests that differential expression could be used by the cell to regulate the response to stress. SIGNIFICANCE A robust technique defines parameters for the dynamic interact...
متن کاملBinding determinants of the small heat shock protein, αB-crystallin: recognition of the 'IxI' motif.
Small heat shock proteins (sHSPs) play a central role in protein homeostasis under conditions of stress by binding partly unfolded, aggregate-prone proteins and keeping them soluble. Like many sHSPs, the widely expressed human sHSP, αB-crystallin ('αB'), forms large polydisperse multimeric assemblies. Molecular interactions involved in both sHSP function and oligomer formation remain to be deli...
متن کاملThe small heat shock proteins and their role in human disease.
Small heat shock proteins (sHSPs) function as molecular chaperones, preventing stress induced aggregation of partially denatured proteins and promoting their return to native conformations when favorable conditions pertain. Sequence similarity between sHSPs resides predominately in an internal stretch of residues termed the alpha-crystallin domain, a region usually flanked by two extensions. Th...
متن کاملMultiple oligomeric structures of a bacterial small heat shock protein.
Small heat shock proteins are ubiquitous molecular chaperones that form the first line of defence against the detrimental effects of cellular stress. Under conditions of stress they undergo drastic conformational rearrangements in order to bind to misfolded substrate proteins and prevent cellular protein aggregation. Owing to the dynamic nature of small heat shock protein oligomers, elucidating...
متن کامل