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Published February 2015 | Published
Journal Article Open

Nitrogenase MoFe protein from Clostridium pasteurianum at 1.08 Å resolution: comparison with the Azotobacter vinelandii MoFe protein


The X-ray crystal structure of the nitrogenase MoFe protein from Clostridium pasteurianum (Cp1) has been determined at 1.08 Å resolution by multiwavelength anomalous diffraction phasing. Cp1 and the ortholog from Azotobacter vinelandii (Av1) represent two distinct families of nitrogenases, differing primarily by a long insertion in the α-subunit and a deletion in the β-subunit of Cp1 relative to Av1. Comparison of these two MoFe protein structures at atomic resolution reveals conserved structural arrangements that are significant to the function of nitrogenase. The FeMo cofactors defining the active sites of the MoFe protein are essentially identical between the two proteins. The surrounding environment is also highly conserved, suggesting that this structural arrangement is crucial for nitrogen reduction. The P clusters are likewise similar, although the surrounding protein and solvent environment is less conserved relative to that of the FeMo cofactor. The P cluster and FeMo cofactor in Av1 and Cp1 are connected through a conserved water tunnel surrounded by similar secondary-structure elements. The long -subunit insertion loop occludes the presumed Fe protein docking surface on Cp1 with few contacts to the remainder of the protein. This makes it plausible that this loop is repositioned to open up the Fe protein docking surface for complex formation.

Additional Information

© 2014 International Union of Crystallography. This is an open-access article distributed under the terms of the Creative Commons Attribution (CC-BY) Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original authors and source are cited. Received 27 October 2014; Accepted 17 November 2014. We thank Dr J. B. Howard for contributions to this project. The work was supported by NIH grant GM45162 to DCR, a National Sciences and Engineering Research Council of Canada postdoctoral fellowship and Caltech Center for Environmental Microbial Interactions fellowships to L-MZ and a National Science Foundation Graduate Research Fellowship (grant DGE-1144469 to CNM). We thank the staff at beamline 12-2, Stanford Synchrotron Radiation Lightsource (SSRL) for their assistance. SSRL is operated for the DOE and supported by its OBER and by the NIH, NIGMS (P41GM103393) and the NCRR (P41RR001209). We acknowledge the Gordon and Betty Moore Foundation, the Beckman Institute and the Sanofi–Aventis Bioengineering Research Program at Caltech for their generous support of the Molecular Observatory at Caltech.

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August 20, 2023
August 20, 2023