Polyoxomolybdate clusters of Mo/W-storage protein

Five years ago, Schemberg et al. reported the crystal structure of molybdenum/tungsten storage protein from Azotobacter vinelandii complexed with polyoxotungstates [1, 2].

Now Kowalewski et al. report the 1.6 Å X-ray structure of the same protein containing a variety of polyoxomolybdate clusters, from Mo₃ to Mo₈ [3].

Some N₂-fixing bacteria prolong the functionality of nitrogenase in molybdenum starvation by a special Mo storage protein (MoSto) that can store more than 100 Mo atoms. The presented 1.6 Å X-ray structure of MoSto from Azotobacter vinelandii reveals various discrete polyoxomolybdate clusters, three covalently and three noncovalently bound Mo₈, three Mo_5–7, and one Mo₃ clusters, and several low occupied, so far undefinable clusters, which are embedded in specific pockets inside a locked cage-shaped (αβ)₃ protein complex. <...> The formed polyoxomolybdate clusters of MoSto, not detectable in bulk solvent, are the result of an interplay between self- and protein-driven assembly processes that unite inorganic supramolecular and protein chemistry in a host–guest system.

1. Schemberg, J., Schneider, K., Demmer, U., Warkentin, E., Müller, A. and Ermler, U. (2007) Towards biological supramolecular chemistry: a variety of pocket-templated, individual metal oxide cluster nucleations in the cavity of a Mo/W-storage protein. Angewandte Chemie International Edition 46, 2408—2413.
2. PDB:2OGX
3. Kowalewski, B., Poppe, J., Demmer, U., Warkentin, E., Dierks, T., Ermler, U. and Schneider, K. (2012) Nature’s polyoxometalate chemistry: X-ray structure of the Mo storage protein loaded with discrete polynuclear Mo–O clusters. J. Am. Chem. Soc. 134, 9768—9774.