FUNCTIONAL ROLE OF WATER IN MEMBRANES UPDATED: A TRIBUTE TO TRÄUBLE.

E. A. DISALVO; A. PINTO; M.F. MARTINI; A.M. BOUCHET; A HOLLMANN; M.A. FRIAS

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 1848 p. 1552 - 1562

0005-2736

The classical view of a cell membrane is as a hydrophobic slab in which only nonpolar solute can dissolve and permeate. However, water soluble non-electrolytes such as glycerol, erythritol, urea and others can permeate lipid membranes in the liquid crystalline state. Moreover, recently polar amino acid?s penetration has been explained by means of molecular dynamics in which appearance of water pockets is postulated. According to Träuble (1971), water diffuses across the lipid membranes by occupying holes formed in the lipid matrix due to fluctuations of the acyl chain trans-gauche isomers. These holes, named ?kinks? have the molecular dimension of CH2 vacancies. The condensation of kinks may form aqueous spaces into which low molecular weight species can dissolve. This molecular view can explain permeability properties considering that water may be distributed along the hydrocarbon chains in the lipid matrix. The purpose of this review is to consolidate the mechanism anticipated by Träuble by discussing recent data in literature that directly correlates the molecular state of methylene groups of the lipids with the state of water in each of them. In addition, the structural properties of water near the lipid residues can be related with the water activity triggering of kink formation by changes in the head group conformation that induces the propagation of kinks along the acyl chains and hence to the diffusion of water.