Complex formation of Vipp1 depends on its alpha-helical PspA-like domain.

Vipp1 (vesicle-inducing protein in plastids 1) is found in Cyanobacteria and chloroplasts of photosynthetic eukaryotes where it is essential for the formation of the thylakoid membrane. Vipp1 is closely related to the phage shock protein A (PspA), a bacterial protein induced under diverse stress conditions. Vipp1 proteins differ from PspA by an additional C-terminal domain that is required for Vipp1 function in thylakoid biogenesis. We show here that in Cyanobacteria, green algae, and vascular plants, Vipp1 is part of a high molecular mass complex. The complex is formed by multiple copies of Vipp1, and complex formation involves interaction of the central alpha-helical domain that is common to Vipp1 as well as to PspA proteins. In chloroplasts of vascular plants, the Vipp1 complex can be visualized by green fluorescent protein fusion in discrete locations at the inner envelope. Green fluorescent protein fusion analysis furthermore revealed that complex formation is important for proper positioning of Vipp1 at the inner envelope of chloroplasts.