Catalyzes the hydration of trans-2-enoyl-CoAs with a chain-length of 4-6 carbon atoms, forming the corresponding (3R)-3-hydroxyacyl-CoAs, which can then be utilized for the production of polyhydroxyalkanoates (PHA) polymers. Cannot use trans-2,3-octenoyl-CoA as substrate. a (3R)-3-hydroxyacyl-CoA = a (2E)-enoyl-CoA + H2O kcat is 728 sec(-1) with crotonyl-CoA as substrate. kcat is 204 sec(-1) with trans-2,3-pentenoyl-CoA as substrate. kcat is 252 sec(-1) with trans-2,3-hexenoyl-CoA as substrate. Homotetramer.