At4g24160, a Soluble Acyl-Coenzyme A-Dependent Lysophosphatidic Acid Acyltransferase

Ananda K Ghosh,Sona Rajakumari,Neha Chauhan,Guenther Daum,Ram Rajasekharan

doi:10.1104/pp.109.144261

Abstract

Human CGI-58 (for comparative gene identification-58) and YLR099c, encoding Ict1p in Saccharomyces cerevisiae, have recently been identified as acyl-CoA-dependent lysophosphatidic acid acyltransferases. Sequence database searches for CGI-58 like proteins in Arabidopsis (Arabidopsis thaliana) revealed 24 proteins with At4g24160, a member of the alpha/beta-hydrolase family of proteins being the closest homolog. At4g24160 contains three motifs that are conserved across the plant species: a GXSXG lipase motif, a HX(4)D acyltransferase motif, and V(X)(3)HGF, a probable lipid binding motif. Dendrogram analysis of yeast ICT1, CGI-58, and At4g24160 placed these three polypeptides in the same group. Here, we describe and characterize At4g24160 as, to our knowledge, the first soluble lysophosphatidic acid acyltransferase in plants. A lipidomics approach revealed that At4g24160 has additional triacylglycerol lipase and phosphatidylcholine hydrolyzing enzymatic activities. These data establish At4g24160, a protein with a previously unknown function, as an enzyme that might play a pivotal role in maintaining the lipid homeostasis in plants by regulating both phospholipid and neutral lipid levels.

Highlights

Human CGI-58 and YLR099c, encoding Ict1p in Saccharomyces cerevisiae, have recently been identified as acyl-CoA-dependent lysophosphatidic acid acyltransferases
CGI-58 was found to localize to the lipid bodies isolated from the mice white adipose tissues, but the LPA acyltransferase (LPAAT) activity in the soluble fraction from adipose tissue was attributed to CGI-58 (Ghosh et al, 2008b)
After identifying the individual protein sequences, we eliminated the repeated sequences by comparisons with theoretical cDNA and genomic DNA sequences in The Arabidopsis Information Resource database. This strategy led to the identification of 24 proteins that were found to be homologous to CGI-58 (Table I)

Summary

Introduction

Human CGI-58 (for comparative gene identification-58) and YLR099c, encoding Ict1p in Saccharomyces cerevisiae, have recently been identified as acyl-CoA-dependent lysophosphatidic acid acyltransferases. A lipidomics approach revealed that At4g24160 has additional triacylglycerol lipase and phosphatidylcholine hydrolyzing enzymatic activities. These data establish At4g24160, a protein with a previously unknown function, as an enzyme that might play a pivotal role in maintaining the lipid homeostasis in plants by regulating both phospholipid and neutral lipid levels. CGI-58 is a member of the a/b-hydrolase family of proteins and has a conserved lipase motif GXNXG, where the Ser is replaced by an Asn. Biochemical characterization of human CGI-58 revealed that it acylates LPA to PA. At4g24160 is a soluble acyltransferase with lipase and phospholipase functions from Arabidopsis belonging to the a/b-hydrolase superfamily of proteins

Methods

Results

Conclusion