Functional role of water in membranes updated: a tribute to Trauble

DISALVO, E. ANIBAL; BOUCHET, A. M.; PINTO, OSCAR; HOLLMANN, AXEL; FRIAS, M DE LOS ANGELES

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

ELSEVIER SCIENCE BV

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

0005-2736

Trauble (1971) postulated that water can diffuse across the lipid membrane by jumping from hole to hole formed in the lipid matrix due to fluctuations of the acyl chain trans gauche isomers. Each water molecule could occupy a kink of the molecular dimension of CH2 vacants. With this visualization several permeability models explained the diffusivity of water molecules across the lipid bilayers. In this regard, kinks were much easier to be formed above the phase transition than below, explaining the sudden increase in water permeation in the fluid state in comparison with the gel state. The triggering of kink formation was related to head group conformational changes that induced the propagation of kinks along the acyl chains and hence to the diffusion of water. In an extension to this model, the permeation of water-soluble non-electrolytes such as glycerol, erythritol, urea and others was explained as a result of the condensation of kinks in order to form an aqueous space with the molecular size of the permeant. Recent studies of aminoacid penetration recall in some extent these ideas. The kink formation or kink condensation is apparently replaced by new ¨structural¨ feature such as pockets. However, neither structural nor thermodynamic correlations with the lipid state and with the water state are done. The purpose of this review is to consolidate the mechanism anticipated by Trauble with direct measures the molecular state of methylene groups of the lipids and the concomitant state of water in each of them.