InterPro domain: IPR020581

The P protein is part of the glycine decarboxylase multienzyme complex (GDC), also annotated as glycine cleavage system or glycine synthase. GDC consists of four proteins P, H, L and T [ 1 ]. The P protein ( 1.4.4.2 ) binds the alpha-amino group of glycine through its pyridoxal phosphate cofactor, carbon dioxide is released and the remaining methylamin moiety is then transferred to the lipoamide cofactor of the H protein. The reaction catalysed by this protein is:

Glycine + lipoylprotein = S-aminomethyldihydrolipoylprotein + CO2

The subunit composition of glycine cleavage system P proteins have been classified into two types. Those from eukaryotes and some of the P proteins from prokaryotes (e.g. Escherichia coli) are in the homodimeric form. The rest of those from prokaryotes are heterotetrameric, with two different subunits which, based on sequence similarities, correspond respectively to the N and C-terminal halves of the eukaryotic subunit [ 2 ].

1. Characterization of the Escherichia coli gcv operon. Gene 142, 17-22
2. Structure of P-protein of the glycine cleavage system: implications for nonketotic hyperglycinemia. EMBO J. 24, 1523-36