Molybdopterin synthase (MPT synthase)

Molybdopterin synthase is a heterotetrameric enzyme complex essential for the biosynthesis of the molybdenum cofactor (MoCo) in humans [1, 2]. It consists of two small subunits (MOCS2A) and two large subunits (MOCS2B), both encoded by the bicistronic MOCS2 gene [3, 22]. The enzyme's primary biological function is to catalyze the conversion of cyclic pyranopterin monophosphate (cPMP, also known as precursor Z) into molybdopterin (MPT) by incorporating two sulfur atoms into the precursor molecule [1, 14]. This step is critical because MoCo is a necessary cofactor for several vital enzymes, including sulfite oxidase, xanthine dehydrogenase, and aldehyde oxidase [2, 39]. Genetic mutations in the MOCS2 gene lead to Molybdenum Cofactor Deficiency Type B (MoCD-B), a rare and severe autosomal recessive metabolic disorder [13, 16]. MoCD-B is characterized by the accumulation of neurotoxic sulfite and S-sulfocysteine, leading to rapid and irreversible brain damage, neonatal seizures, and early childhood death [16, 36]. While MoCD Type A (caused by MOCS1 mutations) can be treated with the substrate replacement therapy Fosdenopterin (Nulibry), there is currently no approved targeted therapy for MoCD Type B, as the defect lies in the MPT synthase enzyme itself [12, 36]. Research into gene therapy and enzyme replacement remains the primary focus for developing future treatments for this condition [28, 35].

Other names

MOCS2Molybdenum cofactor synthesis protein 2MOCO1Molybdopterin synthase catalytic subunitMolybdopterin synthase sulfur carrier subunitMolybdenum cofactor synthesis protein 2 small subunitMolybdenum cofactor synthesis protein 2 large subunitMOCS2AMOCS2BMPT synthase large subunitMPT synthase small subunit

Substrate replacement therapy; Fosdenopterin serves as a synthetic precursor (cyclic pyranopterin monophosphate) that is converted by functional molybdopterin synthase into molybdopterin, thereby restoring the molybdenum cofactor biosynthetic pathway in patients with upstream defects [12, 38].