# Biological Transition Metals

> **NIH NIH R01** · NORTHWESTERN UNIVERSITY · 2022 · $556,215

## Abstract

PROJECT SUMMARY
 Our program is devoted to understanding the function of biologically central transition metals. We here
focus on three key roles of transition-ion centers, and have assembled outstanding multidisciplinary teams to
attack them. The approaches to each incorporate a suite of advanced paramagnetic resonance techniques,
EPR/ENDOR/ESEEM, many of which we have developed. (a) 'Radical-SAM (S-adenosyl methionine)'
Enzymes: This enzyme superfamily is Nature's most widespread means of performing essential radical-based
chemistry. (i) With Broderick, we have demonstrated that throughout the superfamily, reductive SAM cleavage
generates an organometallic intermediate, Omega, central to catalysis. We will probe the properties and reactivity of
Omega through EPR/ENDOR studies of multiple Omega's, in parallel with studies of synthetic Omega-analogs prepared by
Suess. (ii) We revealed that regioselective cleavage of the SAM S−C5’ bond to generate Omega upon SAM
reduction is Jahn-Teller (JT) enabled and active-site controlled. To understand this phenomenon we will study
it with a selected suite of SAM analogues bound in a correspondingly selected suite of RS enzymes, while
computationally exploring the fundamentals of the process with Mosquera. (iii) We will expand the study of the
RS catalytic mechanism, examining substrate transformations by epimerases and spliceases. (b) Mechanism
of Nitrogenase activation: With Dean, Seefeldt, and Raugei we have revealed how the nitrogenase MoFe
protein is activated to carry out perhaps the most challenging chemical transformation in biology, the reduction
of the N≡N triple bond, and have shown that the alternative V- and Fe-nitrogenases employ the same
mechanism. This latter finding will enable us to explore the structure of nitrogenase intermediates throughout
the entire catalytic cycle, using 1,2H/14N ENDOR of substrates. A remarkable achievement of Dean enables us to
monitor the 13C ENDOR of carbide central to the FeMo-co active center, as well. This study is enhanced through
the use of site-selectively 57Fe-labeled FeMo-co in enzyme prepared by Suess, a major advance in integrating
structure and function. (c) in vivo Mn2+ Speciation: We earlier established that EPR/ENDOR/ESEEM
provide an otherwise unavailable means of characterizing Mn2+ complexes in live cells. Our collaboration with
Daly now has shown that Mn2+ speciation is the strongest biological indicator of cellular resistance to ionizing
radiation (IR) throughout the tree of life. In the coming period we will explore a discovery of and correlation
between in vivo Mn2+ speciation, IR resistance, and aging, and test the hypothesis that our spectroscopies can
be used to devise optimized radiotherapy regimens for human tumors. In a dramatic new venture, a
collaboration with O'Halloran surprisingly indicates that Mn2+ ions play an important role in fertilization of
amphibian oocytes, and we will broaden and expand our studies of Mn2+ speciation by exam...

## Key facts

- **NIH application ID:** 10365583
- **Project number:** 2R01GM111097-50
- **Recipient organization:** NORTHWESTERN UNIVERSITY
- **Principal Investigator:** BRIAN M HOFFMAN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $556,215
- **Award type:** 2
- **Project period:** 1979-01-01 → 2026-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10365583

## Citation

> US National Institutes of Health, RePORTER application 10365583, Biological Transition Metals (2R01GM111097-50). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10365583. Licensed CC0.

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