Required for O-acetylhomoserine sulfhydrylase (OAHS)-independent homocysteine (Hcy) biosynthesis. Together with MJ0099, catalyzes the condensation of sulfide with aspartate semialdehyde to generate homocysteine. Likely functions through persulfide intermediate. 3 H(+) + hydrogen sulfide + L-aspartate 4-semialdehyde + reduced 2[4Fe-4S]-[ferredoxin] = H2O + L-homocysteine + oxidized 2[4Fe-4S]-[ferredoxin] The ligand-induced conformational reorganization of the protein could be an important regulatory mechanism. Amino-acid biosynthesis. Homodimer (PubMed:18931440, PubMed:20026078). May form a complex with MJ0099 (By similarity). The C-terminal cystathionine beta-synthase (CBS) domains can bind different numbers of S-adenosyl-L-methionine (SAM) and S-methyl-5'-thioadenosine (MTA) ligands. Binding of SAM and MTA triggers a drastic conformational change in the protein, which evolves progressively from an open form in the absence of ligands to a closed form when the four sites are fully occupied. Belongs to the L-aspartate semialdehyde sulfurtransferase family.