Globular oligomers as the building block units of the filamentous structure of E. coli small heat shock protein IbpA and their holding chaperone activity.

In E. coli, IbpA is a small heat-shock protein, which acts as molecular chaperone with only holdase activity. At normal temperature, IbpA monomers oligomerize to form filamentous structure of molecular weight in mega-Dalton range, whereas at higher temperature, the filaments dissociate into smaller oligomers. However, little is known about the formation of filaments, about their building block units, and about the form whether filaments or small oligomers possess optimum holding chaperone activity. Here advanced biophysical techniques including Atomic Force Microscopy (AFM), transmission electron microscopy (TEM), Dynamic Light Scattering (DLS), PAGE, Absorbance and Fluorescence Spectroscopy were used to explore the raised scientific quarries. Experimental results depict that globular oligomers, made of IbpA monomers, act as building block units of IbpA filaments, which serve as storage form having minimal holding chaperone activity. The filaments dissociate under heat-stress into small oligomers with optimum chaperone activity; this was observed from the filamentous/small oligomeric IbpA-mediated suppression of heat-induced inactivation and aggregation of l-lactate dehydrogenase.