Probing the roles of the only universally conserved leucine residue (Leu122) in the oligomerization and chaperone-like activity of Mycobacterium tuberculosis small heat shock protein Hsp16.3

To understand the role of the only universally conserved hydrophobic residu e among all the members of the sHsp family, this extremely well conserved L eu122 residue in Hsp16.3 was replaced by valine, alanine, asparigine, or as partate residues. Only very small amounts of the L122D and L122N mutant Hsp 16.3 proteins were expressed in the transformed E. coli; however, both the L122V and L122A were readily expressed. The L122V and L122A mutant proteins had similar oligomeric structures to the wild-type protein at room tempera ture. Examination of the L122A mutant protein by native pore gradient PAGE and CD spectroscopy, however, revealed a smaller oligomeric size and differ ent secondary structure at 37 degrees C. Both L122V and L122A mutant protei ns exhibited significantly lowered chaperone activities. Observations repor ted here suggest a very important role of this only universally conserved L eu residue in both the formation of specific oligomeric structures and the molecular chaperone activities of Hsp16.3.