Thylakoid membrane characterization and its interaction with PsbI protein from photosystem II

Žofie Sovová, Rudiger Ettrich

Faculty of Science, University of South Bohemia in České Budějovice and Institute of Nanobiology and Structural Biology GCRC, CAS, Nové Hrady, e-mail: sovova@nh.cas.cz

The thylakoid membrane from cyanobacterium Synechocystis PCC6803 is characterized by means of atomistic and coarse-grained molecular dynamics. Two different compositions reported in the literature are described and potential differences are explored. The major difference between the membranes is found in their phase transition temperatures. Additionally, in the used Martini coarse-grain model the phase transition temperature contains a systematic error. Comparison of atomistic and coarse-grained simulations shows a similar behavior for both kinds of simulations, thus supporting the correctness of our recently published coarse-grain force field parameters.

A structural model of PsbI, a one-transmembrane-helix protein and part of photosystem II, is inserted into the chracterized membrane and its behavior is described. Despite being complexed in photosystem II, PsbI can occur in thylakoid membranes as a single protein. Coarse-grained simulations were used to describe the mutual behavior of a larger number of isolated PsbI in a thylakoid membrane. Througout the simulations, the flexible C-terminal loop does not adopt a stable conformation in isolated PsbI, but it may be stabilized, when the proteins multimerize. We observe a dynamic multimerization of PsbI in the coarse-grained simulations, and describe a tendency to form larger aggregates as the preferable behavior of isolated PsbI in thylakoid membranes.

Support from the Czech Science Foundation, no 13-21053S, is ackowleged.