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A New Type of Metalloprotein: The Mo Storage Protein from Azotobacter vinelandii Contains a Polynuclear Molybdenum–Oxide Cluster
Author(s) -
Fenske Dirk,
Gnida Manuel,
Schneider Klaus,
MeyerKlaucke Wolfram,
Schemberg Jörg,
Henschel Volker,
Meyer AnneKatrin,
Knöchel Arndt,
Müller Achim
Publication year - 2005
Publication title -
chembiochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.05
H-Index - 126
eISSN - 1439-7633
pISSN - 1439-4227
DOI - 10.1002/cbic.200400263
Subject(s) - azotobacter vinelandii , molybdenum , storage protein , chemistry , metalloprotein , oxygen storage , diazotroph , metal , crystallography , nitrogen , nitrogenase , biochemistry , oxygen , inorganic chemistry , nitrogen fixation , gene , organic chemistry
Azotobacter vinelandii is a diazotrophic bacterium characterized by the outstanding capability of storing Mo in a special storage protein, which guarantees Mo‐dependent nitrogen fixation even under growth conditions of extreme Mo starvation. The Mo storage protein is constitutively synthesized with respect to the nitrogen source and is regulated by molybdenum at an extremely low concentration level (0–50 n M ). This protein was isolated as an α 4 β 4 octamer with a total molecular mass of about 240 kg mol −1 and its shape was determined by small‐angle X‐ray scattering. The genes of the α and β subunits were unequivocally identified; the amino acid sequences thereby determined reveal that the Mo storage protein is not related to any other known molybdoprotein. Each protein molecule can store at least 90 Mo atoms. Extended X‐ray absorption fine‐structure spectroscopy identified a metal–oxygen cluster bound to the Mo storage protein. The binding of Mo (biosynthesis and incorporation of the cluster) is dependent on adenosine triphosphate (ATP); Mo release is ATP‐independent but pH‐regulated, occurring only above pH 7.1. This Mo storage protein is the only known noniron metal storage system in the biosphere containing a metal–oxygen cluster.