Metal Ion Dependence of Oligosaccharyl Transferase: Implications for Catalysis

摘要: Oligosaccharyl transferase activity exhibits an absolute requirement for certain divalent metal cations. Studies with reconstituted enzyme suggest a preference ions that can adopt octahedral coordination geometry. In order to gain insight into the specific role of cation in catalysis, we have investigated influence cofactor on catalytic tumover tripeptide substrate Bz- Asn-Leu-Thr-NHMe (1) and closely related sulfur-containing analog, Bz-Asn(yS)-Leu-Thr-NHMe (2). The ion substitution studies reveal 1 is effectively tumed over presence several metal ions (Mn^(2+), Fe^(2+), Mg^(2+), Ca^(2+)). contrast, 2 only glycosylated thiophilic metal cations manganese iron. When oxophilic magnesium calcium, shows minimal behavior. With amide 1, distinct may argue against direct lipid-linked pyrophosphate moiety. This fact, together comparative asparagine- thioasparagine-containing tripeptides, implicates places it proximal peptide binding site.