CLONING OF A COCONUT ENDOSPERM CDNA-ENCODING A 1-ACYL-SN-GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE THAT ACCEPTS MEDIUM-CHAIN-LENGTH SUBSTRATES

Immature coconut (Cocos nucifera) endosperm contains a 1-acylsn-glycer ol-3-phosphate acyltransferase (LPAAT) activity that shows a preferenc e for medium-chain-length fatty acyl-coenzyme A substrates (H.M. Davie s, D.J. Hawkins, J.S. Nelsen [1995] Phytochemistry 39: 989-996). Begin ning with solubilized membrane preparations, we have used chromatograp hic separations to identify a polypeptide with an apparent molecular m ass of 29 kD, whose presence in various column fractions correlates wi th the acyltransferase activity detected in those same fractions. Amin o acid sequence data obtained from several peptides generated from thi s protein were used to isolate a full-length clone from a coconut endo sperm cDNA library. Clone pCGN5503 contains a 1325-bp cDNA insert with an open reading frame encoding a 308-amino acid protein with a calcul ated molecular mass of 34.8 kD. Comparison of the deduced amino acid s equence of pCGN5503 to sequences in the data banks revealed significan t homology to other putative LPAAT sequences. Expression of the coconu t cDNA in Escherichia coli conferred upon those cells a novel LPAAT ac tivity whose substrate activity profile matched that of the coconut en zyme.