Vipp1 structure and function in cyanobacteria and chloroplasts

The vesicle inducing protein in plastids 1 (Vipp1) is an essential
factor for the development and maintenance of the thylakoid
membrane. Depletion of Vipp1 in both Arabidopsis and Synechocystis
mutants severely affects their ability to form thylakoids and
consequently to perform photosynthesis. This work focuses on
structural and functional properties of Vipp1. It was shown that
Vipp1 assembles into a homooligomeric complex of ca. 2000 kDa. The
presence of the Vipp1 complex was detected in cyanobacteria, green
algae and higher plants, thereby identifying oligomerization as an
essential feature for the function of Vipp1. A detailed computer
analysis of Vipp1 secondary structure in different organisms
revealed functionally important characteristics of the protein and
allowed to discern specific features of its C-terminal domain.
Based on the structural analysis, biochemical characterization of
Vipp1 domains was carried out. It appeared that the PspA-like
domain of Vipp1 is responsible for both complex formation and
localisation of Vipp1 at the inner envelope of chloroplasts while
the C-terminal domain is not involved in these processes. In order
to closer elucidate the function of Vipp1, an analysis of
Arabidopsis plants with moderate deficiency in Vipp1 protein level
was performed. From results obtained in this analysis it can be
proposed that Vipp1 acts at the initial stages of thylakoid
biogenesis. Oligomerization of Vipp1 appeared to be a prerequisite
for the process of thylakoid formation to commence. Moreover, the
extent of thylakoid membrane formation is directly correlated to
the amount of Vipp1 protein available in the chloroplast.