Assessing the influence of the lipid and water environment on the proton transfer energetics.

<p>We performed all computations for water-mediated proton transfer (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0201298#pone.0201298.t005" target="_blank">Table 5</a>). (a–b) PMF profiles computed for wild-type C1C2 and K132A with E162 unprotonated (a) and with E162 protonated (b). The PMF profiles were computed for the setups illustrated in panels c–f, namely: full (solid black line), PROT (grey line), DRY (black dashes), K132A (solid magenta line) and K132A-DRY (magenta dashes). (c–f) Representative snapshots for PMF calculations for: wild-type C1C2 with or without a lipid membrane (full/PROT, c); wild-type C1C2 with a lipid membrane, but with some active site waters removed (DRY, d); the K132A mutant in a lipid membrane (K132A, e); and K132A with a lipid membrane, but some active site waters removed (K132A-DRY, f). The corresponding path numbers are given in brackets (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0201298#pone.0201298.t005" target="_blank">Table 5</a>). Note that active site hydration, E162 protonation and the presence of the K132 side chain contribute to the stability of the proton on the retinal Schiff base.