Mobility of Single-File Water Molecules in Aquaporins

Description

Confined water is an important element in protein structure and function, yet its physical properties are notoriously difficult to assess. Here we show that the mobility of single-file waters inside aquaporins reaches bulk water mobility. Our assessment is based on measurements of the unitary water channel permeability, pf [1]. We used stopped-flow experiments to determine the per channel increment in proteoliposome water permeability as a function of protein abundance. Therefore, we substituted (i) semi empirical relationships between vesicle volume and scattered light intensity for an adaptation of the Rayleigh-Gans-Debye equation and (ii) analytically solved the differential equation for the time dependence of vesicle volume on water efflux. Both fluorescence correlation spectroscopy and high speed atomic force microscopy served to determine the exact number of water channels per vesicle. pf increased in this order: aquaporin-Z [2], aquaporin-1 [3], and GlpF (E.coli glycerol facilitator) [4]. The maximal turnover number was equal to 5x1010 s-1, it thus exceeded previous estimates by as much as 50-fold. The high mobility is consistent with previous reports on the low number of hydrogen bonds formed by the single-file waters in the channel and the distorted geometry of those bonds. [1] S. M. Saparov et al., Phys. Rev. Lett. 96, 148101 (2006). [2] P. Pohl, S. M. Saparov, M. J. Borgnia, and P. Agre, Proc. Natl. Acad. Sci. U. S. A. 98, 9624 (2001). [3] S. M. Saparov et al., J. Biol. Chem. 276, 31515 (2001). [4] S. M. Saparov, S. P. Tsunoda, and P. Pohl, Biol. Cell 97, 545 (2005). Author Block: Andreas Horner1, Florian Zocher1, Johannes Preiner1, Nicole Ollinger1, Christine Siligan1, Sergey A. Akimov2, Peter Pohl1. 1Biophysics, Johannes Kepler University, Linz, Austria, 2Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, Russian Federation.

Period	09 Feb 2015
Event title	59th Annual Biophysical Society Meeting
Event type	Conference
Location	United StatesShow on map