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Calcium Regulation of Group VIA “Calcium‐Independent” Phospholipase A2
Author(s) -
Hsu YuanHao,
Dennis Edward A.
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.850.2
Subject(s) - calcium , ankyrin repeat , calmodulin , phospholipase , phospholipase a , biophysics , divalent , phospholipase a2 , biology , cytosol , biochemistry , chemistry , enzyme , organic chemistry , gene
The Group VIA‐2 calcium‐independent phospholipase A 2 (GVIA‐2 iPLA 2 ; iPLA 2 β) is composed of seven consecutive N‐terminal ankyrin repeats, a linker region, and a C‐terminal phospholipase catalytic domain. Unlike cytosolic GIVA PLA 2 or secreted GV PLA 2 , there are no known calcium binding sites on iPLA 2 (Burke, JE, etc. 2009 JLR). Consequently, the activity of iPLA 2 does not require calcium. We previously reported that ATP activated GVIA‐2 iPLA 2 activity (Ackermann, EJ. etc. 1994 JBC; Lio YC. etc. 1998 BBA). In new experiments, ATP activated GVIA‐2 iPLA 2 with a Kd = 0.9 μM in the mixed‐micelle assay. Calcium inhibited GVIA‐2 iPLA 2 in an ATP dependent manner, indicating calcium interfered with the ATP binding to iPLA 2 . We have constructed a structural model of iPLA 2 and verified it by Hydrogen/Deuterium Exchange‐Mass Spectrometry (DXMS) (Hsu, YH, etc. 2009 JBC). DXMS showed ATP bound to the ankyrin repeats 3–5 (regions 207–226, 216–226, 238–240 and 277–299) and caused a decrease of the deuteration rates in H/D exchange in these neutrally to positively charged ankyrin repeats. ATP binding also caused conformational changes on the n‐terminal pseudo‐ankyrin repeats regions (regions 84–104, 87–104, 94–104, 115–125 and 116–125). We also found that calmodulin inhibited iPLA 2 at an IC 50 of 1.2 μM in the existence of 500 μM calcium and 500 μM ATP. Calmodulin and calcium both inhibited GVIA‐2 iPLA 2 , but ATP prevented the inhibition by both calmodulin and calcium. NIH GM 20501