MYCOBACTERIUM-TUBERCULOSIS CHAPERONIN-10 FORMS STABLE TETRAMERIC AND HEPTAMERIC STRUCTURES - IMPLICATIONS FOR ITS DIVERSE BIOLOGICAL-ACTIVITIES

The chaperonin activity of sequence related chaperonin 10 proteins req uires their aggregation into heptameric structures. We describe size-e xclusion chromatography and ultracentrifugation studies that reveal th at while Escherichia coli chaperonin 10 exists as a heptamer, the Myco bacterium tuberculosis chaperonin 10 is tetrameric in dilute solutions and in whole M. tuberculosis lysate. At high protein concentration an d in the presence of saturating amounts of divalent ions, the protein is heptameric. Human chaperonin 10 is predominantly heptameric, althou gh smaller oligomers were detected, These differences in structural as sembly between species may explain differences in biological activity such as antigenicity. Using C-terminal and N-terminal fragments, seque nce 1-25 was identified as indispensable for aggregation. CD spectrosc opy studies revealed that (i) a minimum at 202-204 nm correlates with aggregation and characterizes not only the spectrum of the mycobacteri al protein, but also those of E. coli and human chaperonin 10 proteins ; (ii) the interactions between subunits are of the hydrophobic type; and (iii) the anti-parallel beta-pleated sheet is the main secondary s tructure element of subunits in both tetrameric and heptameric protein s.