Involved in the fermentation of L-glutamate via the hydroxyglutarate pathway (PubMed:3691501). Catalyzes the reversible syn-elimination of water from (R)-2-hydroxyglutaryl-CoA to yield (E)-glutaconyl-CoA (PubMed:3691501, PubMed:7398622, PubMed:7607244). The dehydration mechanism involves a transient one electron reduction of the thioester from (R)-2-hydroxyglutaryl-CoA, generating a ketyl radical (PubMed:7607244). Prior to (E)-glutaconyl-CoA formation, the ketyl radical is subsequently reoxidized by electron transfer back to the HgdA-HgdB complex (CompD) to avoid change in oxidation state of the substrate (PubMed:7607244). The appropriate redox state of dehydratase HgdA-HgdB complex (CompD) is maintained by HgdC (CompA) via hydrolysis of ATP and ATP-dependent electron transfer (PubMed:7607244). Since the electron is recycled, the dehydratase is able to perform several turnovers with only catalytic amounts of ATP and substoichiometric amounts of HgdC (CompA) (PubMed:7607244). (R)-2-hydroxyglutaryl-CoA = (2E)-glutaconyl-CoA + H2O Binds 1 [4Fe-4S] cluster per heterodimer. Binds 1 FMN per heterodimer. Activated by the HgdC. Reversibly inactivated by oxidants such as 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 4-nitrobenzoate, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) and chloramphenicol. Irreversibly inactivated by oxidants such as hydroxylamine and nitrite. Amino-acid degradation; L-glutamate degradation via hydroxyglutarate pathway; crotonoyl-CoA from L-glutamate: step 4/5. The (R)-2-hydroxyglutaryl-CoA dehydratase enzyme system is a heterodimer composed of an alpha subunit (HgdA) and a beta subunit (HgdB). Belongs to the FldB/FldC dehydratase alpha/beta subunit family.