Enoyl-CoA isomerase/hydratase; part of the gene cluster that mediates the biosynthesis of siderophore ferrichrome A which is contributing to organismal virulence (PubMed:17138696, PubMed:20070524). The first step of ferrichrome A biosynthesis is performed by the HMG-CoA synthase hcs1 which catalyzes the generation of HMG-CoA and CoA using acetoacetyl-CoA and acetyl-CoA as substrates (PubMed:20070524). The enoyl-CoA isomerase/hydratase fer4 then catalyzes the conversion of hcs1-produced HMG-CoA to methylglutaconyl-CoA (PubMed:20070524). The acyltransferase fer5 then fuses the fer4-generated methylglutaconyl-CoA with sid1-generated hydroxyornithine to yield methylglutaconyl hydroxyornithine (PubMed:20070524). Methylglutaconyl hydroxyornithine is then available for use by the NRPS fer3 to generate ferrichrome A (PubMed:20070524). a (3S)-3-hydroxyacyl-CoA = a (2E)-enoyl-CoA + H2O a 4-saturated-(3S)-3-hydroxyacyl-CoA = a (3E)-enoyl-CoA + H2O Siderophore biosynthesis. Expression regulated by iron through the urbs1 transcription factor (PubMed:17138696). Impairs the production of ferrichrome A but does not affect the production of ferrichrome (PubMed:20070524). Belongs to the enoyl-CoA hydratase/isomerase family.