The function of membrane-embedded proteins such as ion channels depends
crucially on their conformation. We demonstrate how conformational changes in
asymmetric membrane proteins may be inferred from measurements of their
diffusion. Such proteins cause local deformations in the membrane, which induce
an extra hydrodynamic drag on the protein. Using membrane tension to control
the magnitude of the deformations and hence the drag, measurements of
diffusivity can be used to infer--- via an elastic model of the protein--- how
conformation is changed by tension. Motivated by recent experimental results
[Quemeneur et al., Proc. Natl. Acad. Sci. USA, 111 5083 (2014)] we focus on
KvAP, a voltage-gated potassium channel. The conformation of KvAP is found to
change considerably due to tension, with its `walls', where the protein meets
the membrane, undergoing significant angular strains. The torsional stiffness
is determined to be 26.8 kT at room temperature. This has implications for both
the structure and function of such proteins in the environment of a
tension-bearing membrane.Comment: Manuscript: 4 pages, 4 figures. Supplementary Material: 8 pages, 1
figur
