# Molecular mechanisms of metal-mediated biological functions for NO, O2, and HNO

> **NIH NIH R15** · THE TRUSTEES OF THE STEVENS INSTITUTE OF TECHNOLOGY · 2021 · $446,664

## Abstract

NO has considerable biomedical significance in cardiovascular regulation, immune
response, neurotransmission, and global N-cycle. O2 is vital for many fundamental biological
functions such as bioenergy, metabolism, and redox signaling. HNO also plays significant roles
in vascular relaxation, enzyme activity regulation, and neurological function regulation. Despite
numerous progress in this area, many important questions have not been answered. Building on
our long-term research on biological complexes of NO, O2, and HNO with metalloproteins and
models especially the successful preliminary data in the current grant period, we will provide
some novel results to address three significant questions. Our first objective is to determine one-
electron NO-to-N2O conversion mechanisms via heme models activated by Lewis acids reported
recently, which is different from the conventional two-electron process by bacterial nitric oxide
reductases. To provide a complete understanding of the kinetic and thermodynamic factors of
this new reaction, systematic computational studies will be done to reveal the full reaction
pathways of the reported heme models and explore the pathways for other biologically available
metal, ligand environments, and Lewis acids. Our second objective is to determine rewiring
mechanisms of NO/O2-sensing functions of a heme enzyme. How enzymes differentiate between
two important redox reagents NO and O2 despite their similarity in shape, size, and charge
remain unknown. Our experimental collaborator has recently reversed the NO sensing heme
protein DosS to be O2 sensing via a triple mutant. The proposed work will reveal specific
contributions of each mutation and their combinations on geometric and electronic properties
and protein environment effects. The identified correlations of structural and electronic features
with sensitivity functions will help rational design to rewire redox sensing functions in future
biomedical research. Our third objective is to determine HNO formation mechanisms of a
clinical drug hydroxyurea via heme proteins. The reactions have been experimentally studied
using horseradish peroxidase (HRP) and catalase (CAT) with different reactivities. However,
HNO formation mechanistic details and the origin for such reactivity difference are yet to be
elucidated. The proposed work will calculate the complete reaction pathways for HRP and CAT
using active site models with varying size of nearby residues and full proteins, to reveal basic
mechanisms and roles of active site residues and protein environments for their differential
reactivities. Results from this systematic study may also help identify key structural features to
assist drug design and understanding of related HNO-generation drugs.

## Key facts

- **NIH application ID:** 10291907
- **Project number:** 2R15GM085774-05
- **Recipient organization:** THE TRUSTEES OF THE STEVENS INSTITUTE OF TECHNOLOGY
- **Principal Investigator:** Yong Zhang
- **Activity code:** R15 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $446,664
- **Award type:** 2
- **Project period:** 2008-07-18 → 2025-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10291907

## Citation

> US National Institutes of Health, RePORTER application 10291907, Molecular mechanisms of metal-mediated biological functions for NO, O2, and HNO (2R15GM085774-05). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10291907. Licensed CC0.

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