Structural Characterization of Two CO Molecules Bound to the Nitrogenase Active Site.

As an approach towards unraveling the nitrogenase mechanism, we have studied the binding of CO to the active-site FeMo-cofactor. CO is not only an inhibitor of nitrogenase, but it is also a substrate, undergoing reduction to hydrocarbons (Fischer-Tropsch-type chemistry). The C-C bond forming capabilities of nitrogenase suggest that multiple CO or CO-derived ligands bind to the active site.

An HPF1/PARP1-Based Chemical Biology Strategy for Exploring ADP-Ribosylation.

Strategies for installing authentic ADP-ribosylation (ADPr) at desired positions are fundamental for creating the tools needed to explore this elusive post-translational modification (PTM) in essential cellular processes. Here, we describe a phospho-guided chemoenzymatic approach based on the Ser-ADPr writer complex for rapid, scalable preparation of a panel of pure, precisely modified peptides. Integrating this methodology with phage display technology, we have developed site-specific as well as broad-specificity antibodies to mono-ADPr.

Catalysis-dependent selenium incorporation and migration in the nitrogenase active site iron-molybdenum cofactor.

Dinitrogen reduction in the biological nitrogen cycle is catalyzed by nitrogenase, a two-component metalloenzyme. Understanding of the transformation of the inert resting state of the active site FeMo-cofactor into an activated state capable of reducing dinitrogen remains elusive. Here we report the catalysis dependent, site-selective incorporation of selenium into the FeMo-cofactor from selenocyanate as a newly identified substrate and inhibitor.

Ligand binding to the FeMo-cofactor: structures of CO-bound and reactivated nitrogenase.

The mechanism of nitrogenase remains enigmatic, with a major unresolved issue concerning how inhibitors and substrates bind to the active site. We report a crystal structure of carbon monoxide (CO)-inhibited nitrogenase molybdenum-iron (MoFe)-protein at 1.50 angstrom resolution, which reveals a CO molecule bridging Fe2 and Fe6 of the FeMo-cofactor.