Characterization of protomer interfaces in HslV protease; the bacterial homologue of 20S proteasome.

HslVU, a two-component proteasome-related prokaryotic system is composed of HslV protease and HslU ATPase. HslV protomers assemble in a dodecamer of two-stacked hexameric rings that form a complex with HslU hexamers. The intra- and inter-ring protomer interfaces in the HslV dodecamer underpin the integrity and functionality of HslVU. Structural characterization of HslV from different bacteria illustrated considerable differences in interacting residues, accessible surface and gap volumes at the intra-ring interface that is primarily stabilized by polar interactions. Amino acid residues Lys28, Arg83 and Asp111 have envisaged as hot spots at this HslU-interacting interface. The inter-ring interfaces that are made up of side chain packing of hydrophobic residues are structurally conserved. Hyperthermostable bacterium T. maritima HslV has extensively networked polar/nonpolar interactions and highly packed environment at all interfaces. Present data demonstrates that HslV protomer interfaces perform distinct functions; whereas intra-ring interface participates in HslV:HslU interaction resulting in allosteric activation of HslV protease by HslU, the inter-ring interfaces uphold the oligomeric form of HslV.