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Unravelling the mechanisms controlling heme supply and demand

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journal contribution
posted on 17.06.2021, 14:24 by Galvin C-H Leung, Simon S-P Fung, Andrea E Gallio, Robert Blore, Dominic Alibhai, Emma L Raven, Andrew J Hudson
In addition to heme’s role as the prosthetic group buried inside many different proteins that are ubiquitous in biology, there is new evidence that heme has substantive roles in cellular signaling and regulation. This means that heme must be available in locations distant from its place of synthesis (mitochondria) in response to transient cellular demands. A longstanding question has been to establish the mechanisms that control the supply and demand for cellular heme. By fusing a monomeric heme-binding peroxidase (ascorbate peroxidase, mAPX) to a monomeric form of green-fluorescent protein (mEGFP), we have developed a heme sensor (mAPXmEGFP) that can respond to heme availability. By means of fluorescence lifetime imaging, this heme sensor can be used to quantify heme concentrations; values of the mean fluorescence lifetime (τMean) for mAPX-mEGFP are shown to be responsive to changes in free (unbound) heme concentration in cells. The results demonstrate that concentrations are typically limited to one molecule or less within cellular compartments. These miniscule amounts of free heme are consistent with a system that sequesters the heme and is able to buffer changes in heme availability while retaining the capability to mobilize heme when and where it is needed. We propose that this exchangeable supply of heme can operate using mechanisms for heme transfer that are analogous to classical ligand-exchange mechanisms. This exquisite control, in which heme is made available for transfer one molecule at a time, protects the cell against the toxic effect of excess heme and offers a simple mechanism for heme-dependent regulation in single-molecule steps.

History

Citation

PNAS June 1, 2021 118 (22) e2104008118; https://doi.org/10.1073/pnas.2104008118

Author affiliation

School of Chemistry

Version

VoR (Version of Record)

Published in

Proceedings of the National Academy of Sciences

Volume

118

Issue

22

Pagination

e2104008118

Publisher

National Academy of Sciences

issn

0027-8424

eissn

1091-6490

Acceptance date

15/04/2021

Copyright date

2021

Available date

17/06/2021

Language

en

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