Selenocyanate derived Se-incorporation into the nitrogenase Fe protein cluster

Creators: Buscagan, Trixia M.; Kaiser, Jens T.; Rees, Douglas C.

Abstract

The nitrogenase Fe protein mediates ATP-dependent electron transfer to the nitrogenase MoFe protein during nitrogen fixation, in addition to catalyzing MoFe protein-independent substrate (CO₂) reduction and facilitating MoFe protein metallocluster biosynthesis. The precise role(s) of the Fe protein Fe₄S₄ cluster in some of these processes remains ill-defined. Herein, we report crystallographic data demonstrating ATP-dependent chalcogenide exchange at the Fe₄S₄ cluster of the nitrogenase Fe protein when potassium selenocyanate is used as the selenium source, an unexpected result as the Fe protein cluster is not traditionally perceived as a site of substrate binding within nitrogenase. The observed chalcogenide exchange illustrates that this Fe₄S₄ cluster is capable of core substitution reactions under certain conditions, adding to the Fe protein's repertoire of unique properties.

Additional Information

© 2022, Buscagan et al. This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited. We dedicate this paper to Prof James B Howard and are grateful for our extensive exchanges on cluster atom exchanges—Jim shaped the way we think about the Fe protein and our journeys with nitrogenase. We also thank Dr Javier Fajardo Jr, Dr Shabman Hematian, and team nitro (Dr Stephanie Threatt, Dr Siobhán MacArdle, Dr Rebeccah Warmack and Ailiena Maggiolo) for insightful discussions, Jeffrey Lai for growing Azotobacter vinelandii, and Dr Paul Oyala for EPR training and support. The authors are grateful to the Gordon and Betty Moore Foundation, Don and Judy Voet, and the Beckman Institute at Caltech for their generous support of the Molecular Observatory at Caltech. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The SSRL Structural Molecular Biology Program is supported by the DOE Office of Biological and Environmental Research, and by the National Institutes of Health, National Institute of General Medical Sciences (including P41GM103393). The Caltech EPR Facility is supported by NSF-1531940. This work was supported by the National Institutes of Health (NIH Grant GM45162) and the Howard Hughes Medical Institute (HHMI). This article is subject to HHMI's Open Access to Publications policy. HHMI lab heads have previously granted a nonexclusive CC BY 4.0 license to the public and a sublicensable license to HHMI in their research articles. Pursuant to those licenses, the author-accepted manuscript of this article can be made freely available under a CC BY 4.0 license immediately upon publication. Author contributions. Trixia M Buscagan, Conceptualization, Data curation, Formal analysis, Validation, Investigation, Visualization, Methodology, Writing – original draft, Writing – review and editing; Jens T Kaiser, Data curation, Validation, Methodology, Writing – review and editing; Douglas C Rees, Conceptualization, Supervision, Funding acquisition, Methodology, Project administration, Writing – review and editing. The funders had no role in study design, data collection, and interpretation, or the decision to submit the work for publication. The authors declare that no competing interests exist.

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