title: Phospholipid:diacylglycerol acyltransferase is a multifunctional enzyme involved in membrane lipid turnover and degradation while synthesizing triacylglycerol in the unicellular green microalga Chlamydomonas reinhardtii.
abstract: Many unicellular microalgae produce large amounts (∼20 to 50% of cell dry weight) of triacylglycerols (TAGs) under stress (e.g., nutrient starvation and high light), but the synthesis and physiological role of TAG are poorly understood. We present detailed genetic, biochemical, functional, and physiological analyses of phospholipid:diacylglycerol acyltransferase (PDAT) in the green microalga Chlamydomonas reinhardtii, which catalyzes TAG synthesis via two pathways: transacylation of diacylglycerol (DAG) with acyl groups from phospholipids and galactolipids and DAG:DAG transacylation. We demonstrate that PDAT also possesses acyl hydrolase activities using TAG, phospholipids, galactolipids, and cholesteryl esters as substrates. Artificial microRNA silencing of PDAT in C. reinhardtii alters the membrane lipid composition, reducing the maximum specific growth rate. The data suggest that PDAT-mediated membrane lipid turnover and TAG synthesis is essential for vigorous growth under favorable culture conditions and for membrane lipid degradation with concomitant production of TAG for survival under stress. The strong lipase activity of PDAT with broad substrate specificity suggests that this enzyme could be a potential biocatalyst for industrial lipid hydrolysis and conversion, particularly for biofuel production.
authors.affiliation: Laboratory for Algae Research and Biotechnology, Department of Applied Sciences and Mathematics, Arizona State University, Mesa, AZ 85212, USA.
authors.forename: Kangsup
authors.initials: K
authors.lastname: Yoon
authors.forename: Danxiang
authors.initials: D
authors.lastname: Han
authors.forename: Yantao
authors.initials: Y
authors.lastname: Li
authors.forename: Milton
authors.initials: M
authors.lastname: Sommerfeld
authors.forename: Qiang
authors.initials: Q
authors.lastname: Hu
mesh_terms: D000217:Acyltransferases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D020418:Algal Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D000595:Amino Acid Sequence; D016825:Chlamydomonas reinhardtii / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression; D008049:Lipase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008563:Membrane Lipids / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010843:Pichia / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013379:Substrate Specificity; D014280:Triglycerides / Q000378:metabolism*
chemical_list: D020418:Algal Proteins; D018076:DNA, Complementary; D008563:Membrane Lipids; D012333:RNA, Messenger; D018749:RNA, Plant; D014280:Triglycerides; D000217:Acyltransferases; C426836:phospholipid diacylglycerol acyltransferase; D008049:Lipase