Effect of ethanol on Munc13-1 C1 in membrane: A Molecular Dynamics Simulation Study.
BACKGROUND
Ethanol has a significant effect on synaptic plasticity. Munc13-1 is an essential presynaptic active zone protein involved in priming the synaptic vesicle and releasing neurotransmitter in the brain. It is a peripheral membrane protein and binds to the activator, diacylglycerol (DAG)/phorbol ester at its membrane-targeting C1 domain. Our previous studies identified Glu-582 of C1 domain as the alcohol-binding residue (Das, J. et al, J. Neurochem., 126, 715-726, 2013).


METHODS
Here we describe a 250 ns molecular dynamics (MD) simulation study on the interaction of ethanol and the activator-bound Munc13-1 C1 in the presence of varying concentrations of phosphatidylserine (PS).


RESULTS
In this study, Munc13-1 C1 shows higher conformational stability in ethanol than in water. It forms fewer hydrogen bonds with phorbol 13-acetate in the presence of ethanol than in water. Ethanol also affected the interaction between the protein and the membrane and between the activator and the membrane. Similar studies in a E582A mutant suggest that these effects of ethanol are mostly mediated through Glu-582.


CONCLUSIONS
Ethanol forms hydrogen bonds with Glu-582. While occupancy of the ethanol molecules at the vicinity (4Å) of Glu-582 is 34.4 %, the occupancy in the E582A mutant is 26.5 % of the simulation time. In addition, the amount of PS in the membrane influences the conformational stability of the C1 domain and interactions in the ternary complex. This study is important in providing the structural basis of ethanol's effects on synaptic plasticity.