Protein-protein interactions in fatty acid elongase complexes are important for very-long-chain fatty acid synthesis.

Fatty acid elongase (FAE), which catalyzes the synthesis of very-long-chain fatty acids (VLCFAs), is a multiprotein complex; however, little is known about its quaternary structure. In this study, BiFC and/or yeast two hybrid (Y2H) assays showed that 1) homo-interactions were observed in β-ketoacyl-CoA synthases (KCS2, KCS9, and KCS6), Eceriferum2-like proteins [CER2 and CER2-Like2 (C2L2)], and FAE complex proteins (KCR1, PAS2, ECR, and PAS1), except for CER2-Like1 (C2L1). 2) Hetero-interactions were observed between KCSs (KCS2, KCS9, and KCS6), between CER2-LIKEs (CER2, C2L2, and C2L1), and between FAE complex proteins (KCR1, PAS2, ECR, and PAS1). 3) PAS1 interacts with FAE complex proteins (KCR1, PAS2, and ECR), but not with KCSs (KCS2, KCS9, and KCS6) and CER2-LIKEs (CER2, C2L2, and C2L1). 4) Asp (308 aa) and three Arg (309 to 311 aa) residues of KCS9 were essential for the homo-interactions of KCS9 and hetero-interactions between KCS9 and PAS2 or ECR. An Asp (339 aa) residue of KCS9 is involved in its homo- and hetero-interactions with ECR. Complementation analysis of Arabidopsis kcs9 mutant by the expression of amino acid-substituted KCS9 mutant genes showed that 5) Two Asp residues (308 and 339 aa) of KCS9 are involved in the synthesis of C24 VLCFAs from C22. This study suggests that protein-protein interaction (PPI) in FAE complexes is important for VLCFA synthesis and provides insight into the quaternary structure of FAE complexes for efficient synthesis of VLCFAs.