Conserved domains and evolution of secreted phospholipases A(2).

Secreted phospholipases A(2) (sPLA(2) s) are lipolytic enzymes present in organisms ranging from prokaryotes to eukaryotes but their origin and emergence are poorly understood. We identified and compared the conserved domains of 333 sPLA(2) s and proposed a model for their evolution. The conserved domains were grouped into seven categories according to the in silico annotated conserved domain collections of 'cd00618: PLA(2) _like' and 'pfam00068: Phospholip_A2_1'. PLA(2) s containing the conserved domain cd04706 (plant-specific PLA(2) ) are present in bacteria and plants. Metazoan PLA(2) s of the group (G) I/II/V/X PLA(2) collection exclusively contain the conserved domain cd00125. GIII PLA(2) s of both vertebrates and invertebrates contain the conserved domain cd04704 (bee venom-like PLA(2) ), and mammalian GIII PLA(2) s also contain the conserved domain cd04705 (similar to human GIII PLA(2) ). The sPLA(2) s of bacteria, fungi and marine invertebrates contain the conserved domain pfam09056 (prokaryotic PLA(2) ) that is the only conserved domain identified in fungal sPLA(2) s. Pfam06951 (GXII PLA(2) ) is present in bacteria and is widely distributed in eukaryotes. All conserved domains were present across mammalian sPLA(2) s, with the exception of cd04706 and pfam09056. Notably, no sPLA(2) s were found in Archaea. Phylogenetic analysis of sPLA(2) conserved domains reveals that two main clades, the cd- and the pfam-collection, exist, and that they have evolved via gene-duplication and gene-deletion events. These observations are consistent with the hypothesis that sPLA(2) s in eukaryotes shared common origins with two types of bacterial sPLA(2) s, and their persistence during evolution may be related to their role in phospholipid metabolism, which is fundamental for survival.