Figure 8.

Different fates for Phospho-Ser and Phospho-Thr residues in proteins. (a) Most Ser and Thr side chains that get phosphorylated by protein kinases are ultimately dephosphorylated hydrolytically by protein phosphatase, releasing Pi and regenerating the side chain-OH; some P-Ser/P-Thr intermediates can instead undergo a lyase-mediated reaction, initiated by loss of the C_α-H. P_i is again a product but now a double bond has been created between C_α and C_β of the side chains to yield dehydroAla (dhA) and dehydrobutyrine (dhB) side chains; (b) In lantipeptide maturations some of those dhA and dhB residues can be captured intramolecularly by neighboring thiolate side chains of Cys residues to yield crosslinking lanthionine or methyllanthionine bridges. (c) Posttranslational processing of a –ser-thr-dipeptide moiety in the goadsporin precursor by kinase/lyase (ser) and cyclodehydratase/dehydrogenase (thr) replaces two tandem peptide bonds with a methylene-methyloxazole unit.