The small mechanosensitive channel: Adaptive gating and timing during hypoosmotic shock.

Abstract

Mechanosensation is the ability to respond to mechanical stimuli. It is present in many organisms. In Escherichia coli (E. coli), mechanosensation manifests in two membrane channels, the large mechanosensitive channel (MscL) and the small mechanosensitive channel (MscS). Both osmoregulatory channels sense membrane tension. MscS, the subject of these studies, consists of a transmembrane region and a cytoplasmic cage. It opens at tensions below those which can cause immediate damage to membranes, contrasting with MscL which opens at near-lytic tensions. Because it opens at non-threatening tensions, MscS not only opens and closes but also inactivates. Inactivation is non-conductive and tension insensitive, and this adaptive behavior was first observed on patch clamp. With the aid of carefully constructed molecular models, the first part of this dissertation evaluates whether inactivation is merely a patch clamp artifact or if it is indeed a part of in vivo MscS function. Working with wild type (WT) alongside fast inactivating and noninactivating mutants proved inactivation does confer a survival advantage to hypoosmotically shocked bacteria. Additionally, light scattering was used to view the swelling and channel response events in WT and knock out (KO) cells lacking mechanosensitive channels upon instantaneous hypoosmotic shock by way of stopped flow.