Surface loops of extracellular phospholipase A1 determine both substrate specificity and preference for lysophospholipids

Naoaki Arima; Asuka Inoue; Kumiko Makide; Takamasa Nonaka; Junken Aoki

doi:10.1194/jlr.M022400

Surface loops of extracellular phospholipase A₁ determine both substrate specificity and preference for lysophospholipids[S]

^*Graduate School of Pharmaceutical Sciences, Tohoku University, Miyagi, 980-8578 Japan
^§Department of Structural Biology, School of Pharmacy, Iwate Medical University, Iwate 028-3694, Japan
^†PRESTO, Japan Science and Technology Corporation, Tokyo 102-0076, Japan
^**CREST, Japan Science and Technology Corporation, Tokyo 102-0076, Japan

Abstract

Members of the pancreatic lipase family exhibit both lipase activity toward triacylglycerol and/or phospholipase A₁ (PLA₁) activity toward certain phospholipids. Some members of the pancreatic lipase family exhibit lysophospholipase activity in addition to their lipase and PLA₁ activities. Two such enzymes, phosphatidylserine (PS)-specific PLA₁ (PS-PLA₁) and phosphatidic acid (PA)-selective PLA₁α (PA-PLA₁α, also known as LIPH) specifically hydrolyze PS and PA, respectively. However, little is known about the mechanisms that determine their substrate specificities. Crystal structures of lipases and mutagenesis studies have suggested that three surface loops, namely, β5, β9, and lid, have roles in determining substrate specificity. To determine roles of these loop structures in the substrate recognition of these PLA₁ enzymes, we constructed a number of PS-PLA₁ mutants in which the three surface loops are replaced with those of PA-PLA₁α. The results indicate that the surface loops, especially the β5 loop, of PA-PLA₁α play important roles in the recognition of PA, whereas other structure(s) in PS-PLA₁ is responsible for PS preference. In addition, β5 loop of PS-PLA₁ has a crucial role in lysophospholipase activity toward lysophosphatidylserine. The present study revealed the critical role of lipase surface loops, especially the β5 loop, in determining substrate specificities of PLA₁ enzymes.

Footnotes

↵1 To whom correspondence should be addressed. e-mail: jaoki{at}m.tohoku.ac.jp
Abbreviations:

EL

endothelial lipase

LPA

lysophosphatidic acid

LPS

lysophosphatidylserine

PA

phosphatidic acid

PA-PLA₁α

phosphatidic acid-selective PLA₁α

PC

phosphatidylcholine

PE

phosphatidylethanolamine

PI

phosphatidylinositol

PLA₁

phospholipase A₁

PS

phosphatidylserine

PS-PLA₁

phosphatidylserine-specific PLA₁

TG

triglyceride
↵[S] The online version of this article (available at http://www.jlr.org) contains supplementary data in the form of three figures.