Bioinorganic Chemistry - spectroscopic and kinetic studies on the mechanisms of iron-containing enzymes
Enzymes that contain the transition metal iron in their active sites exhibit great structural and functional diversity and play important roles in almost every aspect of life. The goal of our interdisciplinary research program is to combine biochemical, kinetic, and spectroscopic methods to study Fe-containing enzymes. The main technique used in our laboratory is 57Fe-Mössbauer spectroscopy. This technique provides information about oxidation state, spin state, coordination environment, and nuclearity of all chemically distinct iron species contained in a sample. In addition, it is possible to quantify all iron species. We combine this method with the rapid freeze quench (RFQ) method, and this allows us to monitor changes occuring at an iron site during a biochemical reaction. These studies (in conjunction with other techniques, such as stopped-flow absorption or RFQ EPR) provide detailed insight into the reaction mechanisms of iron-containing proteins.
Our main focus in this area is the oxygen activation reaction of the Fe(II) and α-ketoglutarate(α -KG)-dependent dioxygenase enzyme family. These enzymes play important roles in biochemistry (oxygen sensing and initiation of response to hypoxia, DNA repair, biosynthesis of antibiotics, etc) and they are believed to operate by a common mechanism. In collaboration with the group of J. Martin Bollinger, Jr., we study one member of this class, taurine: α -KG dioxygenase (TauD), and we identified the first reaction intermediate observed in this class of enzymes. This species contains a Fe=O unit, in which the iron is formally in the oxidation state +IV in the high-spin (S= 2) configuration. This species is the key species that abstracts an H-atom from the substrate for subsequent hydroxylation.
We study the electronic structure of several high-valent intermediates using 57Fe-Mössbauer spectroscopy in collaboration with the group of Michael T. Green.
Iron-sulfur cluster enzymes
Our main focus in this area is the study of the ‘Radical-SAM’ enzymes. These enzymes utilize a reduced [4Fe-4S] cluster to cleave S-adenosylmethionine (SAM) to methionine and a 5’-deoxyadenosylradical (5’-dAdo•) intermediate. The 5’-dAdo• is then used for various purposes. For example, we study the enzyme lipoate synthase using 57Fe-Mössbauer spectroscopy with the group of Squire J. Booker.