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<jats:title>Sulfur steps aside for nitrogen</jats:title> <jats:p> Enzymatic conversion of molecular nitrogen to ammonia requires a dance of electrons and protons. The stage for that dance is the nitrogenase cofactor, a carefully constructed cluster of iron, sulfur, and carbon with homocitrate and, in some cases, bicarbonate appendages, as well as a secondary metal ion that defines the class of enzyme. The question of how this cofactor binds nitrogen has been vexingly difficult to answer. Sippel <jats:italic>et al.</jats:italic> report a high-resolution structure of the vanadium nitrogenase with a light atom, interpreted as nitrogen, bound to the FeV cofactor. A sulfur atom is displaced from the cofactor in this structure and is observed resting in a holding site formed by rearrangement of a glutamine residue. The putative bridging nitrogen atom suggests that diatomic nitrogen may bind to the cluster in a head-on manner, with the glutamine side chain stabilizing protonated intermediates as they are reduced. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6383" page="1484" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar2765">1484</jats:related-article> </jats:p>