Role of the N-terminal region of the crenarchaeal sHsp, StHsp14.0, in thermal-induced disassembly of the complex and molecular chaperone activity.

Small heat shock protein is a ubiquitous molecular chaperone, which consists of a non-conserved N-terminal region followed by a conserved alpha-crystallin domain. To understand the role of the N-terminal region, we constructed N-terminal truncation mutants of StHsp14.0, the sHsp from Sulfolobus tokodaii strain 7. All the mutants formed a stable oligomeric complex similar to that of the wild type. Electron microscopy and size exclusion chromatography-multiangle light scattering showed that the N-terminal region should locate in the center of the oligomeric particle. The mutants exhibited reduced chaperone activity for the protection of 3-isopropylmalate dehydrogenase from thermal aggregation. This reduction correlates with lowered subunit exchange efficiency. The oligomeric structure was retained even after incubation at 90 degrees C. These results suggest that the N-terminal region of StHsp14.0 functions in the thermally induced disassembly of the complex.