6GX4

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

(2018) FEBS J 285: 4602-4616

• PubMed: 30367742 Search on PubMed
• DOI: https://doi.org/10.1111/febs.14684
• Primary Citation of Related Structures:  
  6GU5, 6GUJ, 6GWV, 6GX4


• PubMed Abstract: 
  

  A continuous FeMo cofactor supply for nitrogenase maturation is ensured in Azotobacter vinelandii by developing a cage-like molybdenum storage protein (MoSto) capable to store ca. 120 molybdate molecules ( ${\text{MoO}}_{}^{}$ 4 2 - ) 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 relevant states specified by the presence of both ATP/ADP and POM clusters (MoSto _funct ), of only ATP/ADP (MoSto _basal ) and of neither ATP/ADP nor POM clusters (MoSto _zero ), respectively. POM clusters are only produced when ATP is hydrolyzed to ADP and phosphate. V _max was ca. 13 μmol _phosphate ·min ^-1 ·mg ^-1 and K _m for molybdate and ATP/Mg ²⁺ in the low micromolar range. ATP hydrolysis presumably proceeds at subunit α, inferred from a highly occupied α-ATP/Mg ²⁺ and a weaker occupied β-ATP/no Mg ²⁺ -binding site found in the MoSto _funct structure. Several findings indicate that POM cluster storage is separated into a rapid ATP hydrolysis-dependent molybdate transport across the protein cage wall and a slow molybdate assembly induced by combined auto-catalytic and protein-driven processes. The cage interior, the location of the POM cluster depot, is locked in all three states and thus not rapidly accessible for molybdate from the outside. Based on V _max , the entire Mo storage process should be completed in less than 10 s but requires, according to the molybdate content analysis, ca. 15 min. Long-time incubation of MoSto _basal with nonphysiological high molybdate amounts implicates an equilibrium in and outside the cage and POM cluster self-formation without ATP hydrolysis. DATABASES: The crystal structures MoSto in the MoSto-F6, MoSto-F7, MoSto _basal , MoSto _zero , and MoSto-F1 _vitro states were deposited to PDB under the accession numbers PDB 6GU5, 6GUJ, 6GWB, 6GWV, and 6GX4.

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Organizational Affiliation: 

Max-Planck-Institut für Biophysik, Frankfurt am Main, Germany.