Beyond soluble electron carrier: cytochrome cM as a membrane-anchored redox regulator in cyanobacteria
Abstract
Cytochrome cM is a small, highly conserved c-type cytochrome present across diverse cyanobacterial lineages, yet its true physiological function has puzzled researchers for over thirty years. Early efforts placed cytochrome cM as an alternative stress-induced electron carrier bridging photosynthetic and respiratory pathways. This view gained traction due to its widespread distribution, its dramatic induction during environmental stress, and the co-localisation of photosynthetic and respiratory complexes within the thylakoid membrane. However, careful biophysical characterisation revealed an exceptionally low midpoint redox potential (+151 mV) and remarkably slow electron-transfer kinetics towards P700+ —features that are inconsistent with efficient photosynthetic electron transfer. Likewise, direct evidence tying cytochrome cM to respiratory terminal oxidases has remained elusive and frequently contradictory. Interest in cytochrome cM has been reignited by recent physiological studies demonstrating that its removal markedly improves photosynthetic performance and carbon fixation under photomixotrophic conditions. Parallel bioinformatic and structural work has suggested the presence of an N-terminal transmembrane domain and revealed substantial structural similarity to the NorC subunit of bacterial nitric oxide reductases, setting cytochrome cM apart from classical soluble cytochromes. Here, we critically re-examine the historical models, weigh the evidence surrounding its candidate roles, and highlight the emerging concept that cytochrome cM functions primarily as a membrane-anchored redox regulator rather than a classical electron shuttle. Finally, we outline key knowledge gaps and suggest targeted strategies to resolve this long-standing enigma in cyanobacterial bioenergetics.
Related
- Genomic imprinting of the metabolic regulator gene Klf14 is regulated by a paternal sub-TAD anchored at Mest
- Characterization of the key membrane protein cytochrome Cyc2 from Ghiorsea bivora
- Electron Transfer and Binding of the c-Type Cytochrome TorC to the Trimethylamine N-Oxide Reductase in Escherichia coli
- Paralemmin-2 is a membrane-anchored cytoskeletal constituent of Axon Initial Segments and nodes of Ranvier
- STIM1 at the plasma membrane: A novel Molecular regulator of B cell migration.
BibTeX
@article{molinaheredia2026beyond,
title = {{Beyond soluble electron carrier: cytochrome cM as a membrane-anchored redox regulator in cyanobacteria}},
author = {Fernando P. Molina-Heredia and Alejandro Torrado},
journal = {Frontiers in Plant Science},
year = {2026},
month = nov,
doi = {10.3389/fpls.2026.2011183},
url = {https://www.frontiersin.org/articles/10.3389/fpls.2026.2011183},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Beyond soluble electron carrier: cytochrome cM as a membrane-anchored redox regulator in cyanobacteria
AU - Fernando P. Molina-Heredia
AU - Alejandro Torrado
PY - 2026
DA - 2026/11/05
JO - Frontiers in Plant Science
DO - 10.3389/fpls.2026.2011183
UR - https://www.frontiersin.org/articles/10.3389/fpls.2026.2011183
AB - Cytochrome cM is a small, highly conserved c-type cytochrome present across diverse cyanobacterial lineages, yet its true physiological function has puzzled researchers for over thirty years. Early efforts placed cytochrome cM as an alternative stress-induced electron carrier bridging photosynthetic and respiratory pathways. This view gained traction due to its widespread distribution, its dramatic induction during environmental stress, and the co-localisation of photosynthetic and respiratory complexes within the thylakoid membrane. However, careful biophysical characterisation revealed an exceptionally low midpoint redox potential (+151 mV) and remarkably slow electron-transfer kinetics towards P700+ —features that are inconsistent with efficient photosynthetic electron transfer. Likewise, direct evidence tying cytochrome cM to respiratory terminal oxidases has remained elusive and frequently contradictory. Interest in cytochrome cM has been reignited by recent physiological studies demonstrating that its removal markedly improves photosynthetic performance and carbon fixation under photomixotrophic conditions. Parallel bioinformatic and structural work has suggested the presence of an N-terminal transmembrane domain and revealed substantial structural similarity to the NorC subunit of bacterial nitric oxide reductases, setting cytochrome cM apart from classical soluble cytochromes. Here, we critically re-examine the historical models, weigh the evidence surrounding its candidate roles, and highlight the emerging concept that cytochrome cM functions primarily as a membrane-anchored redox regulator rather than a classical electron shuttle. Finally, we outline key knowledge gaps and suggest targeted strategies to resolve this long-standing enigma in cyanobacterial bioenergetics.
SN - 1664-462X
ER -