The Chaperone-like Activity of Rat HspB8/Hsp22 and Dynamic Molecular Transition Related to Oligomeric Architectures In Vitro

HspB8/Hsp22 is a functionally distinct small heat shock proteins (sHsp) and is preferentially expressed in brain, heart, skeletal, and smooth muscle. HspB8 is also associated with neuromuscular function and protein quality control by proteasomes in cardiac hypertrophy. However, the molecular properties in vitro and molecular oligomerization remain uncertain. In this investigation, the rat HspB8 gene was expressed in E. coli cells, and mature HspB8 protein was efficiently prepared. The chaperone-like activity of HspB8 in vitro was quantitatively analyzed by model substrates. Size exclusion chromatography revealed that HspB8 had polydisperse oligomers and underwent dynamic molecular transition in solution, existing in a dynamic equilibrium between various oligomers. In a nonphysiological solution, HspB8 was predominantly octamers. In a physiological solution (pH 7.4), HspB8 mainly formed tetramers. The dynamic interactive transition maybe was helpful to maintain its molecular complxes in solution. In a FRET assay, subunit exchange occurred frequently between the various oligomers with a rate of 0.12, 0.089, and 0.064 min(-1) at 50 degrees C, 43 degrees C, and 37 degrees C, respectively. It also demonstrated the dynamic molecular properties of HspB8 in solution.