2020 Proton Leakage Is Sensed by IM30 and Activates IM30-Triggered Membrane Fusion

Carmen Siebenaller, Benedikt Junglas , Annika Lehmann, Nadja Hellmann and Dirk Schneider

Int. J. Mol. Sci. 2020, 21, 4530; DOI: 10.3390/ijms21124530


Department of Chemistry, Biochemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany


The inner membrane-associated protein of 30 kDa (IM30) is crucial for the development and maintenance of the thylakoid membrane system in chloroplasts and cyanobacteria. While its exact physiological function still is under debate, it has recently been suggested that IM30 has (at least) a dual function, and the protein is involved in stabilization of the thylakoid membrane as well as in Mg2+-dependent membrane fusion. IM30 binds to negatively charged membrane lipids,  preferentially at stressed membrane regions where protons potentially leak out from the thylakoid lumen into the chloroplast stroma or the cyanobacterial cytoplasm, respectively. Here we show in vitro that IM30 membrane binding, as well as membrane fusion, is strongly increased in acidic environments. This enhanced activity involves a rearrangement of the protein structure. We suggest that this acid-induced transition is part of a mechanism that allows IM30 to (i) sense sites of proton leakage at the thylakoid membrane, to (ii) preferentially bind there, and to (iii) seal leaky membrane regions via membrane fusion processes.