Biochemical and Molecular Characterization of Two Phosphatidic Acid-selective Phospholipase A1s, mPA-PLA1α and mPA-PLA1β*

By Tatsufumi Hiramatsu, H. Sonoda, Yasukazu Takanezawa, Rei K. Morikawa, M. Ishida, K. Kasahara, Y. Sanai, R. Taguchi, J. Aoki, H. Arai. Journal of Biological Chemistry, 2003

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We have identified a novel phospholipase A1, named mPA-PLA1β, which is specifically expressed in human testis and characterized it biochemically together with previously identified mPA-PLA1α. The sequence of mPAPLA1β encodes a 460-amino acid protein containing a lipase domain with significant homology to the previously identified phosphatidic acid (PA)-selective PLA1, mPA-PLA1α. mPA-PLA1β contains a short lid and deleted β9 loop, which are characteristics of PLA1 molecules in the lipase family, and is a member of a subfamily in the lipase family that includes mPA-PLA1α and phosphatidylserine-specific PLA1. Both mPA-PLA1β and mPA-PLA1α recombinant proteins exhibited PA-specific PLA1 activity and were vanadate-sensitive. When mPAPLA1β-expressing cells were treated with bacterial phospholipase D, the cells produced lysophosphatidic acid (LPA). In both mPA-PLA1α and β-expressing cells, most of the PA generated by the phospholipase D (PLD) treatment was converted to LPA, whereas in control cells it was converted to diacylglycerol. When expressed in HeLa cells most mPA-PLA1α protein was recovered from the cell supernatant. By contrast, mPA-PLA1β was recovered almost exclusively from cells. Consistent with this observation, we found that mPA-PLA1β has higher affinity to heparin than mPA-PLA1α. We also found that the membrane-associated mPA-PLA1s were insoluble in solubilization by 1% Triton X-100 and were detected in Triton X-100-insoluble buoyant fractions of sucrose gradients. The present study raises the possibility that production of LPA by mPA-PLA1α and -β occurs on detergent-resistant membrane domains of the cells where they compete with lipid phosphate phosphatase for PA.

Subfields: Cell Biology, Molecular Biology, Physiology

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