No abstract

Summary While Vipp1 (also known as IM30) clearly is essential for proper biogenesis of thylakoid membranes in chloroplasts and cyanobacteria, the exact function of Vipp1/IM30 still remains unclear. The recent in vivo study of Gutu et al. now demonstrates that Vipp1/IM30 forms localized puncta specifically at highly curved membrane regions at the cell periphery. These Vipp1/IM30 puncta were found being highly dynamic under normal growth conditions, while it has recently been shown that they stably associate with membranes under high‐light conditions. These observations, together with the observation that other Vipp1/IM30 homologous proteins also form puncta under stress conditions, indicate a protective function of these proteins at stressed membrane regions. However, Gutu et al. additionally show that Vipp1/IM30 is of special importance when growing cells are shifted from dark to light growth conditions, which could be explained by light stress, by thylakoid membrane dynamics and/or by photosystem biogenesis, which is being discussed in this article.

The "inner membrane-associated protein of 30 kDa" (IM30), also known as "vesicle-inducing protein in plastids 1" (Vipp1), is found in the majority of photosynthetic organisms that use oxygen as an energy source, and its occurrence appears to be coupled to the existence of thylakoid membranes in cyanobacteria and chloroplasts. IM30 is most likely involved in thylakoid membrane biogenesis and/or maintenance, and has recently been shown to function as a membrane fusion protein in presence of Mg However, the precise role of Mg in this process and its impact on the structure and function of IM30 remains unknown. Here, we show that Mg binds directly to IM30 with a binding affinity of ∼1 mm Mg binding compacts the IM30 structure coupled with an increase in the thermodynamic stability of the proteins' secondary, tertiary, and quaternary structures. Furthermore, the structural alterations trigger IM30 double ring formation because of increased exposure of hydrophobic surface regions. However, Mg-triggered exposure of hydrophobic surface regions most likely modulates membrane binding and induces membrane fusion.