Prediction of posttranslational modification of proteins from their amino acid sequence

If posttranslational modifications (PTMs) are chemical alterations of the protein primary structure during the protein's life cycle as a result of an enzymatic reaction, then the motif in the substrate protein sequence that is recognized by the enzyme can serve as basis for predictor construction that recognizes PTM sites in database sequences. The recognition motif consists generally of two regions: first, a small, central segment that enters the catalytic cleft of the enzyme and that is specific for this type of PTM and, second, a sequence environment of about 10 or more residues with linker characteristics (a trend for small and polar residues with flexible backbone) on either side of the central part that are needed to provide accessibility of the central segment to the enzyme's catalytic site. In this review, we consider predictors for cleavage of targeting signals, lipid PTMs, phosphorylation, and glycosylation.