INHIBITORS OF BACTERIAL SIGNAL PEPTIDASES

Signal peptidases are serine endoproteinases responsible for the prote olytic removal of N-terminal amino acid signal sequences from pre-secr etory proteins in all cellular lifeforms including bacteria. The demon strated essentiality of the enzymatic activity and the ubiquitous occu rrence in bacteria, coupled with the significant molecular differences between bacterial signal peptidases and those of eukaryotes, define t hese enzymes as potential molecular targets for the development of nov el antibacterial agents. Few compounds are known to inhibit bacterial signal peptidases and the most significant advance in SPase inhibition has been the discovery of penem systems as time dependent irreversibl e inhibitors. They are thought to act via acylation of the active site serine. SPases are only acylated by the 5 (S) under bar penem stereoc hemistry, a stereochemical preference mirrored in other azetidinone co ntaining inhibitors. The implications of this is that the active site serine of SPases approach their substrate from the opposite side of th e peptidic backbone to that of all other serine protease families whos e structures are known. The activity of penems is significantly enhanc ed by the incorporation of a C6 hydroxyethyl substituent, thought to b ind into the S-1 pocket of the enzyme. Penem inhibition of SPases has been demonstrated in vitro, in isolated enzyme assays, and in vivo in pulse-chase assays.