This is an in-class PDB exercise based on the paper "Mechanisms Controlling the Cellular Metal Economy" by Gilston and O'Halloran. Students are asked to visualize the metal binding sites of several proteins discussed in the paper, highlighting unusual metal geometries. After identifying the amino acid residues involved in metal binding, students will discuss the bond structure in terms of HSAB theory. 

This activity is designed to give students a deeper understanding of what post-translational modification does in a metalloenzyme using nitrile hydratase (NHase) as a model system.  The metallo-active site of NHase contains a cobalt(III) center that is bound to an unusual coodination sphere containing bis-amidate, cysteinate, sulfenate (RSO^-), and sulfinate (RSO₂^-) ligands.

This learning objective focuses on the enzyme aconitase.  The iron-sulfur cluster is used to regulate iron in the cell and isomerize citrate for energy – two very different mechanisms.  The activity consists of an introduction to the enzyme and a student discussion on the mechanism of the isomerization of citrate to isocitrate; starting in a small group setting followed by a class debriefing.