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HRASLS3
Group XVI phospholipase A2 also commonly known as adipocyte phospholipase A2 (AdPLA) is an enzyme that in humans is encoded by the ''PLA2G16'' gene.〔(【引用サイトリンク】 url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=11145 )〕 This enzyme has also been identified as PLA2G16, HRASLS3, HREV107, HREV107-3, MGC118754 or H-REV107-1 from studies on class II tumor suppression but not on its enzymatic properties. AdPLA is encoded by a 1.3 kilobase AdPLA messenger RNA and is an 18 kDa protein. It belongs to a superfamily of phospholipase A2 (PLA2) enzymes and is found primarily in adipose tissue. AdPLA regulates adipocyte lipolysis and release of fatty acids through a G-protein coupled pathway involving prostaglandin and EP3. It has also been reported to play a crucial role in the development of obesity in mouse models.
== Enzyme characteristics ==
AdPLA has been characterized in Group XVI as a separate subgroup of the PLA2 family for its distinct properties from other known PLA2s. It bears similarity to its PLA2 family in phospholipase activity and calcium dependence. Unlike other PLA2 enzymes, AdPLA is expressed predominantly in adipose tissue at higher levels than in the rest of the body, more so in white adipose tissue (WAT) than brown adipose tissue (BAT). Its primary enzymatic function is to catalyze the preferential hydrolysis of phosphatidylcholines at the sn-2 position, generating free fatty acids.
AdPLA contains a membrane-spanning domain on the C-terminus, which localizes intracellularly for phospholipase activity in proximity to cyclooxygenase 1 (COX-1). His-23 and Cys-113 residues have been shown to be essential in AdPLA activity, which differs from the known His/Asp catalytic dyad or Ser/His/Asp catalytic triad of other PLA2 enzymes. Gln-129 and Asn-112 have also been shown to be necessary in catalysis but their role is not known.〔
AdPLA activity is calcium and pH dependent. Calcium binds to AdPLA and forms a positively charged oxyanion hole to stabilize a negatively charged transition state, similar to other PLA2 active sites. Whereas asparagine binds to calcium in other PLA2 enzymes, the residue that participates in the creation of oxyanion hole in AdPLA has not yet been verified. Optimum AdPLA activity occurs in relatively basic conditions, between pH 7 and 9, to facilitate formation of a histidine-water complex and subsequent fatty acid hydrolysis.〔
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