Required for O-acetylhomoserine sulfhydrylase (OAHS)-independent homocysteine (Hcy) biosynthesis (PubMed:25315403, PubMed:25938369). Together with MA_1822, catalyzes the condensation of sulfide with aspartate semialdehyde to generate homocysteine (Probable). Likely functions through persulfide intermediate (PubMed:28165724). 3 H(+) + hydrogen sulfide + L-aspartate 4-semialdehyde + reduced 2[4Fe-4S]-[ferredoxin] = H2O + L-homocysteine + oxidized 2[4Fe-4S]-[ferredoxin] Amino-acid biosynthesis. Forms homodimers. May form a complex with MA_1822. Belongs to the L-aspartate semialdehyde sulfurtransferase family.