Oxygen content of transmembrane proteins over macroevolutionary time scales

We observe that the time of appearance of cellular compartmentalization correlates with atmospheric oxygen concentration. To explore this correlation, we predict and characterize the topology of all transmembrane proteins in 19 taxa and correlate differences in topology with historical atmospheric oxygen concentrations. Here we show that transmembrane proteins, individually and as a group, were probably selectively excluding oxygen in ancient ancestral taxa, and that this constraint decreased over time when atmospheric oxygen levels rose. As this constraint decreased, the size and number of communication-related transmembrane proteins increased. We suggest the hypothesis that atmospheric oxygen concentrations affected the timing of the evolution of cellular compartmentalization by constraining the size of domains necessary for communication across membranes. Coming up for air Fossils are conventionally used to trace evolutionary change over time. But we may also preserve our history in our biochemistry. Claudia Acquisti et al . have discovered systematic variation in the ways in which various organisms incorporate oxygen into membrane-spanning proteins. Membrane proteins in compartmentalized prokaryotes and eukaryotes tend to contain more oxygen than those of simpler prokaryotes. This may be an echo of the low atmospheric oxygen on the early Earth.