MOLYBDATE-UPTAKE GENES AND MOLYBDOPTERIN-BIOSYNTHESIS GENES ON A BACTERIAL PLASMID - CHARACTERIZATION OF MOEA AS A FILAMENT-FORMING PROTEINWITH ADENOSINE-TRIPHOSPHATASE ACTIVITY

A gene cluster consisting of homologs to Escherichia coli moaA, moeA, moaC and moaE, which encode enzymes involved in the biosynthesis of mo lybdopterin cofactor (MoCo), and to modA, modB and modC, which encode a high-affinity molybdate transporter, were identified on pAO1 of Arth robacter nicotinovorans near genes of molybdopterin-dependent enzymes involved in nicotine degradation. This gene arrangement suggests a coo rdinated expression of the MoCo-dependent and the MoCo-biosynthesis ge nes and shows that catabolic plasmids may carry the transport and bios ynthetic machinery for the synthesis of the cofactors needed for the f unctioning of the enzymes they encode, pAO1 MoeA functionally compleme nted E. coli moeA mutants. The overexpressed and purified protein, of molecular mass 44500 Da, associated into high-molecular-mass complexes and spontaneously formed gels at concentrations above 1 mg/ml. Transm ission electron microscopy and atomic force microscopy revealed that M oeA forms fibrilar structures. In the presence of Mg2+ MoeA exhibited ATPase activity (0.020 pmol ATP.pmol protein(-1).min(-1)). ATP, ADP or AMP induced the disassembly of the MoeA fibers into aggregates. pAO1 MoeA shows 39% identity to the C-terminal domain of the rat neuroprote in gephyrin. Like gephyrin it binds to neurotubulin, but binds with pr eference to tubulin dimers.