Electrostatic interactions play a critical role in Mycobacterium tuberculosis Hsp16.3 binding of substrate proteins

Mycobacterium tuberculosis Hsp16.3, a member of a small heat shock protein family, has chaperone-like activity in vitro and suppresses thermally or ch emically induced aggregation of proteins. The nature of the interactions be tween Hsp16.3 and the denatured substrate proteins was investigated. A dram atic enhancement of chaperone-like activity of Hsp16.3 upon increasing temp erature was accompanied by decreased ANS-detectable surface hydrophobicity, Hsp16.3 exhibited significantly enhanced chaperone-like activity after pre incubation at 100 degreesC with almost unchanged suffice hydrophobicity. Th e interaction between Hsp16.3 and dithiothreitol-treated insulin B chains w as markedly weakened in the presence of NaCl but greatly enhanced by the ad dition of a low-polarity alcohol, accompanied by significantly increased an d decreased Surface hydrophobicity, respectively A working model for Hsp16. 3 binding to its substrate proteins is proposed.