Title: In-silico study of fatty acid biosynthesis pathway enzymes in microalga Scenedesmus

Scenedesmus is an important, rapidly growing, freshwater microalga because of its significantly high lipid content. However, the molecular basis of fatty acid biosynthesis is scarcely elucidated not only in Scenedesmus but also in microalgae as a whole. Mining the genome of Scenedesmus, we identified some of the crucial enzymes involved in fatty acid biosynthesis pathways such as acetyl-CoA carboxylase (ACC), malonyl-CoA:ACP transacylase (MAT) and fatty-acyl thioesterases (FAT). Detailed comparative analyses of these identified enzymes demonstrated highly significant sequence similarity with homologs of bacteria suggesting an evolutionary linkage. Moreover, the molecular modeling and 3D structures of the chloroplastic enzymes revealed that the overall structural orientation and the catalytic residues are well conserved. On the other hand, biotin protein ligase and cytosolic acetyl-CoA carboxylase isoforms presented some significant differences with respect the previously reported protein models. Our analysis describes some specific features in Scenedesmus fatty acid synthesis enzymes that could be responsible for their particular lipid accumulation profile.