Role of Membrane-Bound Thiol–Disulfide Oxidoreductases in Endospore-Forming Bacteria

Thiol–disulfide oxidoreductases catalyze formation, disruption, or isomerization of disulfide bonds between cysteine residues in proteins. Much is known about the functional roles and properties of this class of redox enzymes in vegetative bacterial cells but their involvement in sporulation has remained unknown until recently. Two membrane-embedded thiol–disulfide oxidoreductases, CcdA and StoA/SpoIVH, conditionally required for efficient production of Bacillus subtilis heat-resistant endospores, have now been identified. Properties of mutant cells lacking the two enzymes indicate new aspects in the molecular details of endospore envelope development. This mini-review presents an overview of membrane-bound thiol–disulfide oxidoreductases in the Gram-positive bacterium B. subtilis and endospore synthesis. Accumulated experimental findings on CcdA and StoA/SpoIVH are reviewed. A model for the role of these proteins in endospore cortex biogenesis in presented.