Focus on O-phosphohydroxylysine, O-phosphohydroxyproline, N¹-phosphotryptophan and S-phosphocysteine

The synthesis and chemistry of the lesser-known phosphoamino acids, O-phosphohydroxylysine, O-phosphohydroxyproline, N¹-phosphotryptophan and S-phosphocysteine are described in detail. In addition, where anything at all is known, the biological synthesis, occurrence and functions of these phosphoamino acids are described. Of these phosphoamino acids, only N¹-phosphotryptophan has not been reported to occur in proteins; however, apart from the roles of S-phosphocysteine in the sugar transporter component (EII) and in catalysis by protein phosphotyrosine phosphatase, little is currently known about the biological roles of the phosphoamino acids when they occur as post-translational modifications.