Submitted on April 2, 2008
Revised on June 25, 2008
Accepted on June 27, 2008
Phase composition of lipoprotein sphingomyelin/cholesterol/PtdCho affects fatty acid specificity of sPLA2s
Arnis Kuksis and Waldemar Pruzanski
Banting and Best Medical Research, University of Toronto, Toronto, Ontario M5G 1L5
Corresponding Author: arnis.kuksis{at}utoronto.ca
Abstract We have previously reported preferential release of polyunsaturated fatty acids during hydrolysis of lipoprotein phosphatidylcholine (PtdCho) by group X secretory phospholipase A2 (sPLA2) and preferential release of oligounsaturated fatty acids during hydrolysis of lipoprotein PtdCho by group V sPLA2, but the mechanism of this selectivity has remained unknown. We now show that the rate and specificity of hydrolysis is affected by relative increases in endogenous SM and FC during the lipase digestion. The highest preference for arachidonate release from LDL and HDL by group X sPLA2 was observed for residual SM/PtdCho molar ratio of 1.2 and 0.4, compared to the respective starting ratios of 0.4 of 0.2, as measured by LC/ESI-MS. Group V sPLA2 showed preferential release of linoleate from LDL and HDL at SM/PtdCho ratio 1.5 and 0.6, respectively. We have attributed the change in fatty acid specificity to segregation of molecular species of PtdCho and of sPLA2s between disordered and ordered SM/FC/PtdCho lipid phases. The increases in SM and FC during digestion with group IIA sPLA2 were more limited and a preferential hydrolysis of any fatty acids was not observed. The significance of SM and FC accumulation during sPLA2 hydrolysis of lipoprotein PtdCho has been previously overlooked.
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