Crystal structure of heat shock protein 15 (Hsp15) from Vibrio cholerae: Novel mode of trimerization and nucleic acid binding properties

Vibrio cholerae, experiences a highly hostile environment at human intestine which trigger the induction of various heat shock genes. VcHsp15, the hslR gene product of V. cholerae O395 is a highly up regulated protein which targets erroneously dislodged 50S subunit upon heat shock that carries a tRNA attached to the abortive nascent polypeptide chain, and recycle it for another round of translation. In this study we report the crystal structure of VcHsp15 at 2.33 Å. Although the structure of VcHsp15 share very similar fold to E. Coli Hsp15 their oligomerization properties are quite different. While EcHsp15 is a monomer, VcHsp15 exhibit a novel trimeric form both in crystal structure and in solution. The putative αL motif of VcHsp15 shares a strikingly similar fold with several RNA binding proteins like ribosomal protein S4 and threonyl-tRNA synthetase. Curiously, their αL motif display a comparable surface charge, albeit extremely low sequence identity, indicating that this motif serves as a basic module to bind RNA.