Speaker
Prof.
Martin Lindén
(Stockholm University)
Description
Unlike their model membrane counterparts, biological
membranes are richly decorated with a heterogeneous assembly
of membrane proteins. These proteins are so tightly packed
that their excluded area interactions can alter the free
energy landscape controlling the conformational transitions
suffered by such proteins. For membrane channels, this
effect can alter the critical membrane tension at which they
undergo a transition from a closed to an open state, and
therefore influence protein function in vivo. Despite their
obvious importance, crowding phenomena in membranes are much
less well studied than in the cytoplasm.
Using statistical mechanics results for hard disk liquids,
we show that crowding induces an entropic tension in the
membrane, which influences transitions that alter the
projected area and circumference of a membrane protein. As a
specific case study in this effect, we consider the impact
of crowding on the gating properties of bacterial
mechanosensitive membrane channels, which are thought to
confer osmoprotection when these cells are subjected to
osmotic shock. We find that crowding can alter the gating
energies by more than 2kT in physiological conditions, a
substantial fraction of the total gating energies in some cases.
Given the ubiquity of membrane crowding, the nonspecific
nature of excluded volume interactions, and the fact that
the function of many membrane proteins involve significant
conformational changes, this specific case study highlights
a general aspect in the function of membrane proteins.
