Catalyzes the reversible hydration of cis-homoaconitate ((Z)-but-1-ene-1,2,4-tricarboxylate) to homoisocitrate ((1R,2S)-1-hydroxybutane-1,2,4-tricarboxylate). Can catalyze neither the dehydration of (R)-homocitrate ((2R)-2-hydroxybutane-1,2,4-tricarboxylate) into cis-homoaconitate in vitro, nor the reverse reaction. Is not active toward (S)-homocitrate, cis-aconitate or citrate as substrate. (2R,3S)-homoisocitrate = cis-homoaconitate + H2O Is not inhibited by lysine. Optimum pH is 8.0. Amino-acid biosynthesis; L-lysine biosynthesis via AAA pathway; L-alpha-aminoadipate from 2-oxoglutarate: step 3/5. Heterodimer of HacA and HacB. Belongs to the LeuD family.