Structural Basis for Phospholyase Activity of a Class III Transaminase Homologue

Pyridoxal-phosphate (PLP)-dependent enzymes catalyse a re- markable diversity of chemical reactions in nature. A1RDF1 from Arthrobacter aurescens TC1 is a fold type I, PLP-dependent enzyme in the class III transaminase (TA) subgroup. Despite sharing 28% sequence identity with its closest structural ho- mologues, including b-alanine:pyruvate and g-aminobutyra- te:a-ketoglutarate TAs, A1RDF1 displayed no TA activity. Activi- ty screening revealed that the enzyme possesses phospholyase (E.C. 4.2.3.2) activity towards O-phosphoethanolamine (PEtN), an activity described previously for vertebrate enzymes such as human AGXT2L1, enzymes for which no structure has yet been reported. In order to shed light on the distinctive features of PLP-dependent phospholyases, structures of A1RDF1 in com- plex with PLP (internal aldimine) and PLP·PEtN (external aldi- mine) were determined, revealing the basis of substrate bind- ing and the structural factors that distinguish the enzyme from class III homologues that display TA activity.A.C. thanks the Principado de Asturias for his postdoctoral fellowship Clarín