Title
Mg2+ -binding triggers rearrangement of the IM30 ring structure, resulting in augmented exposure of hydrophobic surfaces competent for membrane binding
Author
Jennifer Heidrich, Benedikt Junglas, Natalia Grytsyk, Nadja Hellmann, Kristiane Rusitzka, Wolfgang Gebauer, Jürgen Markl, Petra Hellwig, Dirk Schneider
Year
2018
Journal
Journal of Biological Chemistry
Abstract
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 Mg2+. However, the precise role of Mg2+ in this process and its impact on the structure and function of IM30 remains unknown. Here, we show that Mg2+ binds directly to IM30 with a binding affinity of approximately 1 mM. Mg2+-binding compacts the IM30 structure coupled with an increase in the thermodynamic stability of the proteins’ secondary, tertiary and quaternary structure. Furthermore, the structural alterations trigger IM30 double ring formation in vitro due to increased exposure of hydrophobic surface regions. However, in vivo Mg2+-triggered exposure of hydrophobic surface regions most likely modulates membrane binding and induces membrane fusion.
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Protein denaturation, Ligand binding, Biochemistry