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J. Biol. Chem., Vol. 283, Issue 15, 9768-9775, April 11, 2008

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YLR099C (ICT1) Encodes a Soluble Acyl-CoA-dependent Lysophosphatidic Acid Acyltransferase Responsible for Enhanced Phospholipid Synthesis on Organic Solvent Stress in Saccharomyces cerevisiae^*

Ananda K. Ghosh¹, Geetha Ramakrishnan, and Ram Rajasekharan²

From the Department of Biochemistry, Indian Institute of Science, Bangalore 560012, India and School of Arts and Sciences, Monash University, Sunway Campus, 46150 Petaling Jaya, Malaysia

One of the major determinants of organic solvent tolerance is the increase in membrane phospholipids. Here we report for the first time that an increase in the synthesis of phosphatidic acid is responsible for enhanced phospholipid synthesis that confers tolerance to the organic solvent in Saccharomyces cerevisiae. This increase in phosphatidic acid formation is because of the induction of Ict1p, a soluble oleoyl-CoA:lysophosphatidic acid acyltransferase. YLR099C (ICT1) was reported to be maximally expressed during solvent tolerance (Miura, S., Zou, W., Ueda, M., and Tanaka, A. (2000) Appl. Environ. Microbiol. 66, 4883–4889); however, its physiological significance was not understood. In silico analysis revealed the absence of any transmembrane domain in Ict1p. Domain analysis showed that it has a hydrolase/acyltransferase domain with a distinct lipid-binding motif and a lysophospholipase domain. Analysis of ict1 strain showed a drastic reduction in phosphatidic acid suggesting the role of Ict1p in phosphatidic acid biosynthesis. Overexpression of Ict1p in S. cerevisiae showed an increase in phosphatidic acid and other phospholipids on organic solvent exposure. To understand the biochemical function of Ict1p, the gene was cloned and expressed in Escherichia coli. The purified recombinant enzyme was found to specifically acylate lysophosphatidic acid. Specific activity of Ict1p was found to be higher for oleoyl-CoA as compared with palmitoyl- and stearoyl-CoAs. This study provides a mechanism for organic solvent tolerance from the point of membrane dynamics in S. cerevisiae.

Received for publication, October 10, 2007 , and in revised form, February 4, 2008.

^* This work was supported by a grant from the Department of Biotechnology (New Delhi, India) under the program support for nonconventional yeasts. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of University Grants Commission fellowship, New Delhi, India.

² To whom correspondence should be addressed: Dept. of Biochemistry, Indian Institute of Science, Bangalore 560012, India. Tel.: 91-80-23602627; Fax: 91-80-23600814; E-mail: lipid{at}biochem.iisc.ernet.in.

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