Glycerophosphodiester phosphodiesterase-like domain of spider venom sphingomyelinases D, bacterial phospholipase D, and similar proteins
This subfamily corresponds to the glycerophosphodiester phosphodiesterase-like domain (GDPD-like) present in sphingomyelinases D (SMases D) (sphingomyelin phosphodiesterase D, EC 126.96.36.199) from spider venom, the Corynebacterium pseudotuberculosis Phospholipase D (PLD)-like protein from pathogenic bacteria, and the Ajellomyces capsulatus H143 PLD-like protein from ascomycetes. Spider SMases D and bacterial PLD proteins catalyze the Mg2+-dependent hydrolysis of sphingomyelin producing choline and ceramide 1-phosphate (C1P), which possess a number of biological functions, such as regulating cell proliferation and apoptosis, participating in inflammatory responses, and playing a key role in phagocytosis. In the presence of Mg2+, SMases D can function as lysophospholipase D and hydrolyze lysophosphatidylcholine (LPC) to choline and lysophosphatidic acid (LPA), which is a multifunctional phospholipid involved in platelet aggregation, endothelial hyperpermeability, and pro-inflammatory responses. Loxosceles spider venoms' SMases D are the principal toxins responsible for dermonecrosis and complement dependent haemolysis induced by spider venom. Due to amino acid substitutions at the entrance to the active-site pocket, some members lack activity. The typical GDPD domain consists of a TIM barrel and a small insertion domain named as the GDPD-insertion (GDPD-I) domain, which is specific for GDPD proteins. Although proteins in this family contain a non-typical GDPD domain which lacks the GDPD-I, their catalytic mechanisms are based on Mg2+-dependent acid-base reactions similar to GDPD proteins. They might be divergent members of the GDPD family. Moreover, this family does not belong to phospholipase D (PLD) superfamily, since it lacks the conserved HKD sequence motif that characterizes the catalytic center of the PLD superfamily. It belongs to the superfamily of PLC-like phosphodiesterases.