Building the stator of the yeast vacuolar-ATPase -: Specific interaction between subunits E and G

The vacuolar (H+)-ATPase (or V-ATPase) is a membrane protein complex that is structurally related to F-1 and F-0 ATP synthases. The V-ATPase is composed of an integral domain (V-0) and a peripheral domain (V-1) connected by a central stalk and up to three peripheral stalks. The number of peripheral stalks and the proteins that comprise them remain controversial. We have expressed subunits E and G in Escherichia coli as maltose binding protein fusion proteins and detected a specific interaction between these two subunits. This interaction was specific for subunits E and G and was confirmed by co-expression of the subunits from a bicistronic vector. The EG complex was characterized using size exclusion chromatography, cross-linking with short length chemical cross-linkers, circular dichroism spectroscopy, and electron microscopy. The results indicate a tight interaction between subunits E and G and revealed interacting helices in the EG complex with a length of about 220 Angstrom. We propose that the V-ATPase EG complex forms one of the peripheral stators similar to the one formed by the two copies of subunit b in F-ATPase.