Abstract
Vipp1 (vesicle inducing protein in plastids 1) is proposed to play a role in thylakoid biogenesis. It is closely related to PspA (phage shock protein A), a bacterial protein that is induced under stress conditions, except that a C-terminal domain of about 20-30 amino acids is present in all Vipp1 proteins but is missing in PspA. Despite its discovery a decade ago and extensive analysis in cyanobacteria, green algae and higher plants, the precise role of Vipp1 in the process of chloroplast development remains unclear. Recently, we found that unfixed chloroplasts in one of the vipp1 mutants (hcf155) were unusually swelled into the ball-shape structure, which resulted from extraordinary space between envelope and thylakoid. Treatment of intact chloroplasts with thermolysin and trypsin revealed that a majority of Vipp1 protein was associated with chloroplast envelope and was tethered to both membranes. Based on our careful western analysis in Arabidopsis and pea, we conclude that Vipp1 protrudes its C-terminus into the outside of chloroplasts. The mutant phenotype and the topology of Vipp1 in envelopes suggest that Vipp1 plays a role in maintaining chloroplast envelope integrity.
