<p> This entry describes the molybdopterin biosynthesis protein MoeB in <taxon tax_id="562">Escherichia coli</taxon> and related species. MoeB and MoaD are involved in molybdenum cofactor biosynthesis, an evolutionarily conserved pathway. The MoeB enzyme covalently modifies the molybdopterin synthase MoaD by sulphurylation. The crystal structure of the complex between the E. coli MoeB and MoaD proteins reveals a MoeB(2)-MoaD(2) heterotetramer in which the MoeB subunits form a mainly hydrophobic dimer [<cite idref="PUB00011756"/>]. </p> <p>MoeB is closely related to ThiF, a thiamine biosynthesis enzyme that modifies ThiS by an analogous adenylation. Both MoeB and ThiF belong to the HesA/MoeB/ThiF family (<db_xref db="INTERPRO" dbkey="IPR000594"/>). </p>