#ccpem — Public Fediverse posts

The last couple of weeks, I was busy preparing for the #CCPEM Spring Symposium and then attending it and presenting at it. So I am only finding time now to share a new preprint that went online earlier this month: https://doi.org/10.64898/2026.04.02.716132

It is about the regulation of CsoSCA, the carbonic anhydrase (CA) found in alpha-carboxysomes. Through a combination of stopped-flow #kinetics, #bioinformatics and #cryoEM, we showed that this enzyme is sensitive to redox conditions. This likely keeps it inactive in the reducing cytosol, where CA activity would short-circuit the CO2 concentration mechanism by turning cytosolic bicarbonate into CO2, which can diffuse through membranes. This redox sensitivity also activates CsoSCA inside mature carboxysomes, because their interior becomes oxidizing as their shell excludes cytosolic reductants.
Overall, CsoSCA's redox sensitivity conditions its activation to its correct encapsulation in carboxysomes.

Turns out visualizing a regulatory disulfide by #cryoEM is difficult! In this case, the strongest evidence for it comes from activity measurements and site-directed mutagenesis. But the structures revealed a conformational equilibrium that we would not have suspected, had we not attempted to solve structures of the enzyme in the active and inactive conditions.

This was excellent team work with first author Nikole and all others, with a real cross-talk between the biochemistry and structures!