Water exclusion from the hydrophobic core is a paradigm of
protein stability. Protein function, in contrast, often requires
water penetration into the nonpolar interior. Biomolecular proton
conduction occurs through transiently solvated hydrophobic channels,
as in the proton pumps cytochrome c oxidase and bacteriorhodopsin, or
in the mono-oxygenase cytochrome P450. Water itself is selectively
transported across biological membranes through predominantly
hydrophobic, not hydrophilic channels, as in aquaporin-1. Why do
water molecules occupy such narrow hydrophobic channels where they
are, at best, able to form two hydrogen bonds, and thus lose many kT
in energy compared to bulk solution? How do water molecules and
protons get into, through, and out of such hydrophobic channels? An
analysis of the water and proton transport through the simplest
molecular hydrophobic channel, a carbon nanotube, addresses these
questions and sheds new light on the functional role of hydrophobic
channels in proteins.
Copyright. All Rights Reserved.