  Water near hydrophobic surfaces is like that at a liquid-vapor interface,
where fluctuations in water density are substantially enhanced compared to that
in bulk water. Here we use molecular simulations with specialized sampling
techniques to show that water density fluctuations are similarly enhanced, even
near hydrophobic surfaces of complex biomolecules, situating them at the edge
of a dewetting transition. Consequently, water near these surfaces is sensitive
to subtle changes in surface conformation, topology, and chemistry, any of
which can tip the balance towards or away from the wet state, and thus
significantly alter biomolecular interactions and function. Our work also
resolves the long-standing puzzle of why some biological surfaces dewet and
other seemingly similar surfaces do not.
