%0 Journal Article
%T Diverse Functions of Secretory Phospholipases A2
%A Preetha Shridas
%A Nancy R. Webb
%J Advances in Vascular Medicine
%D 2014
%R 10.1155/2014/689815
%X Phospholipase A2 enzymes (PLA2s) catalyze the hydrolysis of glycerophospholipids at their sn-2 position releasing free fatty acids and lysophospholipids. Mammalian PLA2s are classified into several categories of which important groups include secreted PLA2s (sPLA2s) and cytosolic PLA2s (cPLA2s) that are calcium-dependent for their catalytic activity and calcium-independent cytosolic PLA2s (iPLA2s). Platelet-activating factor acetylhydrolases (PAF-AHs), lysosomal PLA2s, and adipose-specific PLA2 also belong to the class of PLA2s. Generally, cPLA2 enzymes are believed to play a major role in the metabolism of arachidonic acid, the iPLA2 family to membrane homeostasis and energy metabolism, and the sPLA2 family to various biological processes. The focus of this review is on recent research developments in the sPLA2 field. sPLA2s are secreted enzymes with low molecular weight (with the exception of GIII sPLA2), Ca2+-requiring enzymes with a His-Asp catalytic dyad. Ten enzymatically active sPLA2s and one devoid of enzymatic activity have been identified in mammals. Some of these sPLA2s are potent in arachidonic acid release from cellular phospholipids for the biosynthesis of eicosanoids, especially during inflammation. Individual sPLA2 enzymes exhibit unique tissue and cellular localizations and specific enzymatic properties, suggesting their distinct biological roles. Recent studies indicate that sPLA2s are involved in diverse pathophysiological functions and for most part act nonredundantly. 1. Introduction Secreted phospholipases A2 (sPLA2s) are secreted from a variety of cells and act in autocrine or paracrine manners on cell membranes and other extracellular phospholipids, including lipoprotein particles, surfactant and dietary lipids, microbial membranes, and microvesicles£¿£¿[1]. Even though sPLA2s are considered to act as extracellularly requiring millimolar concentrations of Ca2+, few in vitro reports also indicate possible intracellular activity prior to or during secretion£¿£¿[2]. To date, eleven sPLA2 enzymes, group IB (GIB), group IIA (GIIA), group IIC (GIIC), group IID (GIID), group IIE (GIIE), group IIF (GIIF), group III (GIII), group V (GV), group X (GX), group XIIA (GXIIA), and group XIIB (GXIIB), have been identified in mammals [3¨C5]. GIII sPLA2 is an atypical sPLA2 that contains unique N-terminal and C-terminal domains and a central sPLA2 domain, the S domain, which has higher homology with bee venom sPLA2 (a prototypic group III enzyme) than with other known mammalian sPLA2s [6]. Another unique member is GXIIB protein which has structural
%U http://www.hindawi.com/journals/avm/2014/689815/