Members of the LanL family of
lanthionine synthetases consist of three catalytic domains, an N-terminal pSer/pThr
lyase domain, a central Ser/Thr
kinase domain, and a C-terminal
lanthionine cyclase domain. The N-terminal
lyase domain has sequence homology with members of the OspF family of effector
proteins. In this study, the residues in the
lyase domain of VenL that are conserved in the active site of OspF
proteins were mutated to evaluate their importance for catalysis. In addition, residues that are fully conserved in the LanL family but not in the OspF family were mutated. Activity assays with these
mutant proteins are consistent with a model in which Lys80 in VenL deprotonates the α-
proton of pSer/pThr residues to initiate the elimination reaction. Lys51 is proposed to activate this
proton by coordination to the carbonyl of the pSer/pThr, and His53 is believed to protonate the
phosphate leaving group. These functions are very similar to the corresponding homologous residues in OspF
proteins. On the other hand, recognition of the
phosphate group of pSer/pThr appears to be achieved differently in VenL than in the OspF
proteins. Arg156 and Lys103 are thought to interact with the
phosphate group on the basis of a structural homology model.