Catalyzes the first and rate-limiting reaction of the four reactions that constitute the long-chain fatty acids elongation cycle. This endoplasmic reticulum-bound enzymatic process allows the addition of 2 carbons to the chain of long- and very long-chain fatty acids (VLCFAs) per cycle. Condensing enzyme that catalyzes the synthesis of polyunsaturated very long chain fatty acid (C20- and C22-PUFA), acting specifically toward polyunsaturated acyl-CoA with the higher activity toward C20:4(n-6) acyl-CoA. May participate in the production of polyunsaturated VLCFAs of different chain lengths that are involved in multiple biological processes as precursors of membrane lipids and lipid mediators. a very-long-chain acyl-CoA + H(+) + malonyl-CoA = a very-long-chain 3-oxoacyl-CoA + CO2 + CoA (7Z,10Z,13Z,16Z,19Z)-docosapentaenoyl-CoA + H(+) + malonyl-CoA = (9Z,12Z,15Z,18Z,21Z)-3-oxotetracosapentaenoyl-CoA + CO2 + CoA (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoyl-CoA + H(+) + malonyl-CoA = (7Z,10Z,13Z,16Z,19Z)-3-oxodocosapentaenoyl-CoA + CO2 + CoA (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + H(+) + malonyl-CoA = (7Z,10Z,13Z,16Z)-3-oxodocosatetraenoyl-CoA + CO2 + CoA (7Z,10Z,13Z,16Z)-docosatetraenoyl-CoA + H(+) + malonyl-CoA = (9Z,12Z,15Z,18Z)-3-oxotetracosatetraenoyl-CoA + CO2 + CoA Lipid metabolism; polyunsaturated fatty acid biosynthesis. The C-terminal di-lysine motif may confer endoplasmic reticulum localization. Belongs to the ELO family. ELOVL2 subfamily.