Cloning and functional analysis of putative malonyl-CoA:acyl-carrier protein transacylase gene from the docosahexaenoic acid-producer Schizochytrium sp. TIO1101

Abstract

Malonyl-CoA:acyl-carrier protein transacylase (MCAT), which transfers the malonyl group from malonyl-CoA to holo-acyl carrier protein (ACP), is a key enzyme in fatty acid biosynthesis. Schizochytrium sp. TIO1101 is a marine protist with high levels of docosahexaenoic acid accumulation. In this study, the putative fabD gene coding MCAT was isolated from Schizochytrium sp. TIO1101. The Schizochytrium MCAT gene (ScTIOfabD) contained an 1176bp open reading frame encoding a protein of 391 amino acids. The ScTIOfabD gene exhibited high novelty in nucleotide and amino acid sequence. The highest amino acid identity was only 35% between ScTIOMCAT and the reported MCATs. Further studies demonstrated that ScTIOMCAT could bind malonyl-CoA directly and transfer malonyl group from malonyl-CoA to the ACP domain in vitro. Phylogenetic analysis suggested that ScTIOMCAT was relative close to MCATs of yeast strains. Overexpression of ScTIOMCAT in Saccharomyces cereviseae significantly increased the MCAT activity, without negative effects on the growth rate of the host strain. In addition, ScTIOMCAT generated 16.8 and 62% increase in biomass and fatty acid accumulation, respectively, and did not alter the profile of fatty acid. Our results indicated that the novel MCAT gene from Schizochytrium sp. TIO1101 was crucial for fatty acid synthesis and had potential applications for genetic modifications of oil-producing species.