Does natural selection optimize molecular biomachinery at the quantum level? I present statistical characterizations of molecular dynamics at an interprotein electron transfer (ET) interface. In simulations of the native protein complex, the most frequently occurring molecular configurations afford superior electronic coupling due to the consistent presence of a single water molecule hydrogen-bonded between the donor and acceptor sites. The persistence of this water bridge is attributed to a "molecular breakwater" composed of several hydrophobic residues surrounding the acceptor site. The breakwater supports the function of solvent-organizing residues by limiting the exchange of water molecules between the sterically constrained ET region and the surrounding bulk. When the breakwater's structure is altered by a mutation, bulk solvent molecules disrupt the water bridge, resulting in reduced electronic coupling. These results indicate that protein surface residues stabilize interprotein solvent dynamics to enable ET along a single molecular pathway.