# Allosteric regulation of human cystathionine beta-synthase

> **NIH NIH F32** · UNIVERSITY OF MICHIGAN AT ANN ARBOR · 2022 · $67,174

## Abstract

Project Summary
Regulation of the transsulfuration pathway is key to maintaining healthy levels of the sulfur metabolites,
homocysteine and hydrogen sulfide (H2S). Dysfunction of the first enzyme in this pathway, cystathionine β-
synthase (CBS) results in homocystinuria and affects four major organ systems. CBS catalyzes the condensation
of serine and homocysteine, generating cystathionine and water. Alternatively, it can catalyze the condensation
of cysteine and homocysteine, generating cystathionine and H2S. CBS is a modular protein in which the central
catalytic domain is flanked by an N-terminal heme domain and a C-terminal S-adenosylmethionine (AdoMet)
domain, both of which are regulatory. Long range communication is involved in allosteric regulation of CBS with
the distance between the heme and active site being ~20 Å and between the heme and AdoMet sites, being ~50
Å. A subset of patient mutations map to the linker region between the catalytic and C-terminal domains, and is
predicted to perturb allosteric regulation by AdoMet and in turn, AdoMet-responsive regulation of the heme
domain. I hypothesize that the linker mutations disfavor the conformational transition from the basal to the
activated state that is triggered by AdoMet. I will test my hypothesis by addressing the following aims. (i) I will
characterize the steady-state kinetic parameters of the pathogenic linker mutations (G347S, K384E/N, and M39I)
in the canonical and H2S-producing reactions catalyzed by CBS and the binding constant for AdoMet. I will
assess the impact of the linker mutations on the flux of sulfur through the transsulfuration pathway. (ii) I will
investigate the effects of the linker mutations on the heme redox environment by determining the reduction
potential of the bound heme. The kinetic and binding constants of CO and NO• binding to ferrous heme in the
presence and absence of AdoMet will be determined by stopped-flow spectrophotometry. (iii) I will crystallize the
linker mutants and determine the structure of full-length CBS. Successful completion of these studies will
broaden our understanding of how CBS is regulated and deepen insights into the mechanism of long-range
communication between distal regulatory domains.

## Key facts

- **NIH application ID:** 10381000
- **Project number:** 1F32GM144988-01
- **Recipient organization:** UNIVERSITY OF MICHIGAN AT ANN ARBOR
- **Principal Investigator:** Joseph V. Roman
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $67,174
- **Award type:** 1
- **Project period:** 2022-07-01 → 2025-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10381000

## Citation

> US National Institutes of Health, RePORTER application 10381000, Allosteric regulation of human cystathionine beta-synthase (1F32GM144988-01). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10381000. Licensed CC0.

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