Catalyzes the third of the four reactions of the long-chain fatty acids elongation cycle. This endoplasmic reticulum-bound enzymatic process, allows the addition of two carbons to the chain of long- and very long-chain fatty acids/VLCFAs per cycle. This enzyme catalyzes the dehydration of the 3-hydroxyacyl-CoA intermediate into trans-2,3-enoyl-CoA, within each cycle of fatty acid elongation. Thereby, it participates in the production of VLCFAs of different chain lengths that are involved in multiple biological processes as precursors of membrane lipids and lipid mediators. In tooth development, may play a role in the recruitment and the differentiation of cells that contribute to cementum formation. May also bind hydroxyapatite and regulate its crystal nucleation to form cementum. a very-long-chain (3R)-3-hydroxyacyl-CoA = a very-long-chain (2E)-enoyl-CoA + H2O (3R)-hydroxyhexadecanoyl-CoA = (2E)-hexadecenoyl-CoA + H2O (3R)-hydroxyoctadecanoyl-CoA = (2E)-octadecenoyl-CoA + H2O (3R)-hydroxyeicosanoyl-CoA = (2E)-eicosenoyl-CoA + H2O (3R)-hydroxydocosanoyl-CoA = (2E)-docosenoyl-CoA + H2O (3R)-hydroxytetracosanoyl-CoA = (2E)-tetracosenoyl-CoA + H2O (3R)-hydroxyhexacosanoyl-CoA = (2E)-hexacosenoyl-CoA + H2O Lipid metabolism; fatty acid biosynthesis. Isoform 1: May interact with enzymes of the ELO family (including ELOVL1); with those enzymes that mediate condensation, the first of the four steps of the reaction cycle responsible for fatty acids elongation, may be part of a larger fatty acids elongase complex (PubMed:18554506). Isoform 2: Homooligomer. Self-assembles into spheres which then aggregates to form strings and a meshwork that may support hydroxyapatite crystal nucleation (PubMed:25263524). Isoform 1 is highly expressed in the myocardium, and to a lesser extent in skeletal and smooth muscular tissues including those from stomach, jejunum, and bladder. Also detected in gingival fibroblasts, periodontal ligament cells, osteoblasts and cementoblasts (PubMed:11054553, PubMed:22067203). Isoform 2 is specifically expressed by cementoblasts but also detected in periodontal ligament cells, heart, liver and kidney (at protein level) (PubMed:22067203). Isoform 1 is expressed in fetal heart. N-glycosylated. The gene represented in this entry may be involved in disease pathogenesis. A loss-of-function mutation that segregates with the disease was found in four members of a consanguineous family and not identified in unaffected controls. The mutation affects the expression of the mRNA and the produced protein is catalytically inactive. Catalytically inactive since it lacks the active site but may have an alternative function. Belongs to the very long-chain fatty acids dehydratase HACD family. Isoform 1 shares some similarity with tyrosine phosphatase proteins but it has probably no phosphatase activity. Extended N-terminus. Extended N-terminus.