Estimation of disk membrane lateral pressure and molecular area of rhodopsin by the measurement of its orientation at the nitrogen-water interface from an ellipsometric study

Abstract

The internal lateral pressure of a bilayer has been estimated by numerous investigators. Most of these measurements were made by using the monolayer technique. In our approach, the disk membrane lateral pressure was estimated by assuming that this value is equal to the surface pressure necessary to maintain the transmembrane orientation of rhodopsin. The orientation of rhodopsin at the nitrogen-water interface was determined by using ellipsometry, which can measure the thickness of the film. By examining surface pressure and ellipsometric isotherms of intact and partially hydrolyzed rhodopsin, we have determined that a lateral pressure of 38 mN/m is necessary to give rhodopsin its natural transmembrane orientation and that surface pressures exceeding 45 mN/m lead to the formation of multilayers in the disk membrane film. At 38 mN/m, pure rhodopsin is found to have a molecular area of 2300 A2.

Dielectric properties of Bauhinia monandra and Concanavalin A lectin monolayers, part I

“…A protein under such conditions normally maintains its secondary structure, but loses its original 3D conformation [10]. Different protein monolayers were found to be stable and preserve their native conformation after spreading [11][12][13]. For instance, Korenbrot and Pramik showed that the conformation of rhodopsin at an interface was similar to that found in its native environment [14].…”

Comparison between the behavior of different hydrophobic peptides allowing membrane anchoring of proteins

“…In contrast, the R9AP-Cter peptide is the most highly ordered one with the thinnest amide I bandwidth in the presence of a DOPE monolayer. Nevertheless, the MIP of this peptide is larger than the postulated lateral pressure of membranes [206][207][208][209][210][211][212][213]. Measurements with additional lipids in different physical states could allow to improve our understanding of the relationship between MIP values and peptide secondary structure.…”

“…The determination of the MIP can provide information on the affinity of a peptide for a given type of lipid [205] as well as on its extent of binding to membranes. Indeed, given that the membrane lateral pressure has been estimated in the range of 30-35 mN/m [206][207][208][209][210][211][212][213], one can postulate that a MIP larger than this value will suggest that the peptide could bind membranes. The synergy is obtained by adding 1 to the slope of the plot of the surface pressure increase (ΔΠ) as a function of the initial surface pressure (Π i ) [116].…”

Molecular recognition on the supported and on the air/water interface-spread protein monolayers

“…A protein under such conditions normally maintains its secondary structure, but loses its original 3D conformation [19]. The degree to which protein monolayers are compressed was found to considerably affect the orientation of molecules at the interfaces [20,21].…”