Brian M. Hoffman Electron-nuclear double resonance (ENDOR) of metalloenzymes

Research Interests

We determine the catalytic mechanisms of metalloenzymes through the development and implementation of electron-nuclear double resonance (ENDOR) spectroscopy, a combination of NMR and EPR in which the NMR of active-site nuclei is acquired by monitoring the EPR of the metal center. This technique is uniquely able to determine active site composition and electronic and geometric structures, not merely for an enzyme resting state but, most importantly, for key catalytic intermediates trapped by rapid freeze-quench (rfq), or by cryogenic photolysis of an rfq sample. Characterization of an enzyme’s key intermediates reveals mechanism!

Among the array of ongoing projects partially reflected in recent publications, are studies of multiple central issues at the intersections of Inorganic Chemistry/ Biochemistry/Biology. (i) Biological "nitrogen fixation" – the reduction of N₂ to two NH₃ molecules by the enzyme nitrogenase – the source of ~50% of the N atoms in humans today; (ii) catalysis of H-atom transfer by enzymes of the vast radical SAM (S-adenosyl methionine) superfamily, comprising over 500,000 members, which initiate radical reactions by homolytic cleavage of SAM to form the highly reactive 5’-deoxyadenosyl radical (5’-dAdo•); (iii) Cu methane monooxygenase, which oxidizes methane to methanol and is central to mitigating emissions of methane, the potent greenhouse gas; (iv) in vivo speciation of Mn²⁺ as determined by EPR/ENDOR, which cannot be achieved by cellular fractionation, thereby identifying in vivo Mn²⁺ complexes with biologically central roles: as primary defenders against radiation, in controlling vertebrate fertilization, and as indicators of the likelihood of the persistence of viable lifeforms on Mars!

Parallel studies of synthetic, biomimetic complexes provide constraints that help identify intermediates trapped during catalysis, and that are moreover of intrinsic importance as Jahn-Teller active systems that exhibit novel dynamic properties.

Selected Publications

End-on Copper(I) Superoxo and Cu(II) Peroxo and Hydroperoxo Complexes Generated by Cryoreduction/Annealing and Characterized by EPR/ENDOR Spectroscopy. Davydov R, Herzog AE, Jodts RJ, Karlin KD, and Hoffman BM. Journal of the American Chemical Society. 2022 January 12;144(1):377-389.

Metal ion fluxes controlling amphibian fertilization. Seeler JF, Sharma A, Zaluzec NJ, Bleher R, Lai B, Schultz EG, Hoffman BM, LaBonne C, Woodruff TK, and O'Halloran TV. Nature Chemistry. 2021 July;13(7):683-691.

Exploring the Role of the Central Carbide of the Nitrogenase Active-Site FeMo-cofactor through Targeted ¹³C Labeling and ENDOR Spectroscopy. Pérez-González A, Yang Z-Y, Lukoyanov DA, Dean DR, Seefeldt LC, and Hoffman BM. Journal of the American Chemical Society. 2021 June 23;143(24):9183-9190.

Active-Site Controlled, Jahn−Teller Enabled Regioselectivity in Reductive S−C Bond Cleavage of S-Adenosylmethionine in Radical SAM Enzymes. Impano S, Yang H, Jodts RJ, Pagnier A, Swimley R, McDaniel EC, Shepard EM, Broderick WE, Broderick JB, and Hoffman BM. Journal of the American Chemical Society. 2021 January 13;143(1):335-348.

Particulate methane monooxygenase contains only mononuclear copper centers. Ross MO, MacMillan F, Wang J, Nisthal A, Lawton TJ, Olafson BD, Mayo SL, Rosenzweig AC, and Hoffman BM. Science. 2019 May 10;364(6440):566-570. 

View all publications by Brian M. Hoffman listed in the National Library of Medicine (PubMed). Current and former IBiS students in blue.