α-Crystallin Domains of Five Human Small Heat Shock Proteins (sHsps) Differ in Dimer Stabilities and Ability to Incorporate Themselves into Oligomers of Full-Length sHsps

Abstract

The α-crystallin domain (ACD) is the hallmark of a diverse family of small heat shock proteins (sHsps). We investigated some of the ACD properties of five human sHsps as well as their interactions with different full-length sHsps. According to size-exclusion chromatography, at high concentrations, the ACDs of HspB1 (B1ACD), HspB5 (B5ACD) and HspB6 (B6ACD) formed dimers of different stabilities, which, upon dilution, dissociated to monomers to different degrees. Upon dilution, the B1ACD dimers possessed the highest stabilities, and those of B6ACD had the lowest. In striking contrast, the ACDs of HspB7 (B7ACD) and HspB8 (B8ACD) formed monomers in the same concentration range, which indicated the compromised stabilities of their dimer interfaces. B1ACD, B5ACD and B6ACD transiently interacted with full-length HspB1 and HspB5, which are known to form large oligomers, and modulated their oligomerization behavior. The small oligomers formed by the 3D mutant of HspB1 (mimicking phosphorylation at Ser15, Ser78 and Ser82) effectively interacted with B1ACD, B5ACD and B6ACD, incorporating these α-crystallin domains into their structures. The inherently dimeric full-length HspB6 readily formed heterooligomeric complexes with B1ACD and B5ACD. In sharp contrast to the abovementioned ACDs, B7ACD and B8ACD were unable to interact with full-length HspB1, the 3D mutant of HspB1, HspB5 or HspB6. Thus, their high sequence homology notwithstanding, B7ACD and B8ACD differ from the other three ACDs in their inability to form dimers and interact with the full-length small heat shock proteins. Having conservative primary structures and being apparently similar, the ACDs of the different sHsps differ in terms of their dimer stabilities, which can influence the heterooligomerization preferences of sHsps.

8-Br-cGMP activates HSPB6 and increases the antineoplastic activity of quinidine in prostate cancer

“…HSPB6 , a crucial member of the heat shock protein family B, plays a significant role in smooth muscle contraction [ 26 ]. Similar to other heat shock proteins, HSPB6 exhibits chaperone-like activity and has been shown to prevent heart failure [ 27 , 28 ].…”

A novel αB-crystallin R123W variant drives hypertrophic cardiomyopathy by promoting maladaptive calcium-dependent signal transduction

“…How CRYAB and the R123W variant modulate calcineurin activity, if at all, remains unclear. A recent structural study uncovered that both R120 and R123 are located in the β7–8 sheets of the crystallin domain ( 53 ). However, whereas R120 maintains solubility of CRYAB via forming salt bridges with D109 of the dimerization partner ( 53 ), R123 does not appear to participate in such activity.…”

“…A recent structural study uncovered that both R120 and R123 are located in the β7–8 sheets of the crystallin domain ( 53 ). However, whereas R120 maintains solubility of CRYAB via forming salt bridges with D109 of the dimerization partner ( 53 ), R123 does not appear to participate in such activity. It is thus perhaps not surprising that the R123W variant did not induce protein aggregation compared to its R120G counterpart.…”

HspB5 Chaperone Structure and Activity Are Modulated by Chemical-Scale Interactions in the ACD Dimer Interface

“…Structural and functional studies have suggested that sHsp dimers may be the most active chaperone species; however, unraveling the complexity between structure and function for substrates remains challenging [ 1 , 5 ]. The dimer interface in the ACD of all sHsps is relatively similar in primary and secondary structure, with a canonical anti-parallel β6–β7 sheet forming the interface ( Figure 1 and Figure 7 ) [ 50 , 93 ]. The interface is stabilized by a series of salt bridges from backbone interactions and electrostatic interactions mediated by side chains [ 69 , 76 ].…”

“…D109A is a mutation linked to myofibrillar myopathy pathology, and D109H has been associated with cataract and myopathy in five blood-related individuals [ 42 , 43 ]. In dimerized HspB5, D109 makes a salt bridge to R107 on the same monomer and forms hydrogen bonds with Y122 on the opposite monomer [ 15 , 71 , 93 , 98 , 100 ]. Previous work has shown that D80 interacts with both R107 and R120 to stabilize electrostatic repulsions between the arginine residues, and [ 42 ] has proposed that in the case of D109A, the R120-D80-R107 interactions were partially preserved, because alanine could not interact with R107 or Y122 [ 42 ].…”