Measurements of conformational changes during adhesion of lipid and protein (polylysine and S‐layer) surfaces

Abstract

The adhesion forces between various surfaces were measured using the "surface forces apparatus" technique. This technique allows for the thickness of surface layers and the adhesion force between them to be directly measured in controlled vapor or liquid environments. Three types of biological surfaces were prepared by depositing various lipid-protein monolayers (with thicknesses ranging from 1 to 4 nm) on the inert, molecularly smooth mica surface: (i) hydrophobic lipid monolayers; (ii) amphiphilic polyelectrolyte surfaces of adsorbed polylysine; and (iii) deposited bacterial S-layer proteins. The adhesion, swelling, and wetting properties of these surfaces was measured as a function of relative humidity and time. Initial adhesion is due mainly to the van der Waals forces arising from nonpolar (hydrophobic) contacts. Following adhesive contact, significant molecular rearrangements can occur which alter their hydrophobic-hydrophilic balance and increase their adhesion with time. Increased adhesion is generally enhanced by (i) increased relative humidity (or degree of hydration); (ii) increased contact time; and (iii) increased rates of separation. The results are likely to be applicable to the adhesion of many other biosurfaces, and show that the hydrophobicity of a lipid or protein surface is not an intrinsic property of that surface but depends on its environment (e.g., on whether it is in aqueous solution or exposed to the atmosphere), and on the relative humidity of the atmosphere. It also depends on whether the surface is in adhesive contact with another surface and-when considering dynamic (nonequilibrium) conditions-on the time and previous history of its interaction with that surface.

Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements

“…The smaller increase in adhesion force for the N-phob substrate in Fig. 4 cannot be explained by this approach; it is possible that subtle time-dependent surface changes due to air exposure can produce such an effect (27).…”

Relationship Between Wettability and Lubrication Characteristics of the Surfaces of Contacting Phospholipid-Based Membranes

“…It can be inferred from these results that the initially very hydrophobic surfaces became more hydrophilic (or more adhesive) when they came in contact with water. When a drop of water was placed on a dry l - a -dipalmitoyl-phosphatidylethanoloamine (DPPE) bilayer covered mica surface, the contact angle was 112°, a very hydrophobic surface, and θ = 10° and 60°, after 5 s and 100 s exposure to water, respectively [43]. …”

An in Situ Infrared Spectroscopic Investigation of Lysine Peptide and Polylysine Adsorption to TiO2 from Aqueous Solutions

“…Polylysine is a well-characterized synthetic polymer, which is also utilized in many facets of (bio)chemistry. It has been attached to negatively charged surfaces to facilitate cell adhesion (25), used as a model polyelectrolyte in adsorption studies (26,27), and also as a ligand in polypeptide-metal complexes which simulate catalytic enzymatic systems (28,29). Polylysine can adopt different secondary structures in aqueous solution and these different forms have been identified using IR spectroscopy (22,30).…”