How Lipids use Short, Strong H-Bonds for Membrane Stability, Making ATP & More

Abstract

Short, strong H-bonds (SSHB’s) were first recognized by F. H. Westheimer and O. T. Benfey in 1956. They consist of multi-oxygen anions such as carboxyls, phosphates or sulfates forming tight H-bonds, with other multi-oxygen anions. Westheimer called them acid-anions because the resulting complex was both an acid and a basic anion. He was studying the pK shifts of maleic acid (cis-2-succinate) pK’s (pK1 = 1.9, pK2 = 6.3) vs. those of fumarate (trans-2-succinate) pK1 = 3.1, pK2 = 4.6). He explained the remarkable difference by the fact that the maleate carboxyls are rammed against each other trapping a proton between the anions, using resonance of the 4 oxygens sharing a charged electron by resonance. Thus maleic acid has only one charge and 2 carboxyls between pH 2.0 and 6.8. These H-bonds vary in length from 2,45 to 2.65 A and have been detected in proteins by 1) highly deshielded resonances (15-20 ppm); D/H fractionation factors 5kcal/mol. Typical H-bonds in proteins and nucleic acids are 2.7-3.0A in length and 2±1 kcal/mol in strength. SSHBs are commonly held proximal by external forces such as protein conformation or hydrophobic forces between chains. They are not typically observed by X-ray measurements, however the protons are far up-field in proton NMR. Examples will be discussed on the stability fatty acid vesicles, the use of cardiolipin’s conformation in bilayers, the stability of chlorosulfolipid membranes of Chrysomonads and in the stability of other example membranes.