Component of a hydro-lyase with broad substrate specificity for cis-unsaturated tricarboxylic acids. Catalyzes both the reversible dehydration of (R)-homocitrate ((R)-2-hydroxybutane-1,2,4-tricarboxylate) to produce cis-homoaconitate ((Z)-but-1-ene-1,2,4-tricarboxylate), and its hydration to homoisocitrate ((1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate). Is also able to hydrate the analogous longer chain substrates cis-homo(2)-aconitate, cis-homo(3)-aconitate. These reactions are part of the biosynthesis pathway of coenzyme B. (2R)-homocitrate = (2R,3S)-homoisocitrate (2R)-homocitrate = cis-homoaconitate + H2O (2R,3S)-homoisocitrate = cis-homoaconitate + H2O cis-(homo)2aconitate + H2O = (2R,3S)-iso(homo)2citrate cis-(homo)3aconitate + H2O = (2R,3S)-iso(homo)3citrate Organic acid metabolism; 2-oxosuberate biosynthesis. Heterotetramer of 2 HacA and 2 HacB proteins. Belongs to the aconitase/IPM isomerase family. LeuC type 2 subfamily.