HslVU physiology and biochemistry

Low expression levels and the lability of the HslVU complex make work with proteins from wild-type strains difficult. Gratifyingly, the active protease can be reconstituted in vitro from over-expressed and purified components (Rohrwild et al. 1996). It requires ATP for the degradation of folded substrates and ATP or some of its analogs for the purification of small chromogenic peptides. As expected, ATP-hydrolysis and proteolysis activities are mutually dependent (Seol et al. 1997). In addition, the peptidase activity was found to depend in complex ways on the presence of various cations, especially K in the buffers (Huang and Goldberg 1997). 

All 12 active sites of HslV are located on the inner walls of the hollow particle. In the E. coli particle, each active site has neighboring active sites 28 A away on the same ring and 22 A and 26 A away on the opposite ring. The environment of the nucleophilic Thrl looks similar to that in proteasomes, and the presence of a (putatively protonated) lysine residue near the active site probably helps to lower the pKa of the N-terminal a-amino group so that it is present in the unprotonated form, which can act as the general base to accept a proton from Thrl. 

---