Antibodies to a soluble liver antigen/liver pancreas (SLA/LP) appear to be highly specific for the diagnosis of autoimmune hepatitis. The SLA/LP target antigen was recently identified as a hitherto unknown gene encoding 474 amino acid residues. The function of this antigen remains unclear, because it does not share sequence homology with proteins of known function stored in any of the publicly accessible databases. Therefore we used a new theoretical method called fold recognition and could show that the SLA/LP sequence is compatible with the architecture of the superfamily of pyridoxal phosphate (PLP; vitamin B6)-dependent transferases. Its function is likely to be that of a serine hydroxymethyltransferase and may be an important enzyme in the thus far poorly understood selenocysteine pathway.