The Molybdenum Storage Protein: A soluble ATP hydrolysis ‐dependent molybdate pump

Polyoxomolybdate cluster storage of the molybdenum storage protein is separated into a rapid ATP hydrolysis ‐dependent molybdate transport across the proteinous cage wall and a slow protein‐promoted and ATP‐independent molybdate self‐assembly process. Polyoxomolybdate clusters are formed in specific protein pockets supported by the high molybdate concentrations accumulated inside the cage provided via the molybdate pump. A continuous FeMo cofactor supply for nitrogenase maturation is ensured inAzotobacter vinelandii by developing a cage ‐like molybdenum storage protein (MoSto) capable to store ca. 120 molybdate molecules () as discrete polyoxometalate (POM) clusters. To gain mechanistic insight into this process, MoSto was characterized by Mo and ATP/ADP content, structural, and kinetic analysis. We defined three functionally rel evant states specified by the presence of both ATP/ADP and POM clusters (MoStofunct), of only ATP/ADP (MoStobasal) and of neither ATP/ADP nor POM clusters (MoStozero), respectively. POM clusters are only produced when ATP is hydrolyzed to ADP and phosphate.Vmax was ca. 13 μmolphosphate·min−1·mg−1 andKm for molybdate and ATP/Mg2+ in the low micromolar range. ATP hydrolysis presumably proceeds at subunit α, inferred from a highly occupied α‐ATP/Mg2+ and a weaker occupied β‐ATP/no Mg2+‐binding site found in the MoStofunct structure. Several findings indicate that POM cluster storage is separated into a rapid ATP hydrolysis ‐d...
Source: FEBS Journal - Category: Research Authors: Tags: Original Article Source Type: research