ABSTRACT
While His and Cys predominate as ligands of catalytic and structural zinc atoms, respectively, Asp and His predominate in cocatalytic zinc sites where the frequency is Asp > His > Glu> Cys. Ser, Thr, Asn, Lys, Tyr, and backbone carbonyls (e.g., Trp) have been found to be ligands to the bridging zinc sites. The ligands to these sites often come from nearly the entire length of the protein. The metals in these sites may therefore be important to the overall fold of the protein as well as catalytic function. The ligands are often at the ends of (3 sheets or come from short “ loop” stretches of amino acids connecting (3 sheets and a helices.
