Surface layer proteins properties

Surface layer proteins (S-layers) represent a unique self-assembling system. Their remarkable property of self-assembUng and their repetitive physicochemical properties, down to the nanometer scale, are promising for various applications. 

Chapter 3, Self-assembly of nanobiomaterials, prepared by Varga et al., offers a recent review regarding the surface-layer proteins (S-layers) that represent a unique self-assembling system. Their remarkable property of self-assembling and their repetitive physicochemical properties down to the nanometer scale led to various applications in the fields of bio- and nanotechnology. Chapter 3 focuses on the basic principles and self-assembly properties of the S-layer protein of Sporosarcina ureae. 

The anisotropy in the physicochemical surface properties and differences in the surface topography of S-layer lattices allowed the determination of the orientation of the monolayers with respect to different surfaces and interfaces. Since in S-layers used for crystallization studies the outer surface is more hydrophobic than the inner one, the protein lattices were generally oriented with their outer face against the air-water interface [120,121]. Crystallization studies with the S-layer protein fromB. coagulansE i Nl at different lipid monolayers [122] revealed that the S-layer lattice is attached to lipid monolay-... 

The robust observation of surface hydration dynamics on two time scales and a series of correlations with protein properties provides a molecular picture of water motions and their coupling with protein fluctuations in the layer, as shown in Fig. 46. The dynamic exchange of hydration layer water with outside bulk... 

Stratum corneum, the nonliving layer of skin, is refractory as a substrate for chemical reactions, hut it has a strong physical affinity for water. The chemical stability of stratum corneum is evident in its mechanical barriers which include insoluble cell membranes, matrix-embedded fibers, specialized junctions between cells, and intercellular cement. The hygroscopic properties of stratum corneum appear to reside in an 80 A-thick mixture of surface-active proteins and lipids that forms concentric hydrophilic interfaces about each fiber. This combination of structural features and surface-active properties can explain how stratum corneum retains body fluids and prevents disruption of living cells by environmental water or chemicals. 

Caseinate is a mixture of fairly flexible polymers. Most proteins are of globular conformation, and their surface properties are not easy to interpret. The values of t)ls are much higher and tend to increase with the age of the film. It may take a day to obtain a more or less constant value, which is typically 0.1-0.5 N s m 1. However, the surface layer is clearly viscoelastic, and the apparent viscosity obtained will strongly depend on measurement conditions, especially the shear rate. Actually, it cannot always be ruled out that the proteinaceous surface layer is subject to yielding or fracture upon large deformation this would imply that slip occurs in the rheometer, leading to a greatly underestimated viscosity. 

Adsorption at solid/liquid interfaces has some peculiarities as compared with fluid/fluid interfaces. The chemical nature of the solid surface and its properties (charge, hydrophobicity, etc.) determine the mode and strength of binding, as well as, in many cases, the conformational changes in adsorbed protein molecules. The solid surfaces can be easily modified and tuned up for specific types of interactions. Usually, in contrast to fluid surfaces, solid surfaces are not chemically or energetically uniform, and their heterogeneity may result in nonuniform adsorption of protein layers. Finally, adsorption from solutions is always a competitive process, and in the simplest case competition between a protein and a solvent takes place. 

Some consequences which result from the proposed models of equilibrium surface layers are of special practical importance for rheological and dynamic surface phenomena. For example, the rate of surface tension decrease for the diffusion-controlled adsorption mechanism depends on whether the molecules imdergo reorientation or aggregation processes in the surface layer. This will be explained in detail in Chapter 4. It is shown that the elasticity modulus of surfactant layers is very sensitive to the reorientation of adsorbed molecules. For protein surface layers there are restructuring processes at the surface that determine adsorption/desorption rates and a number of other dynamic and mechanical properties of interfacial layers. 

This brief review conprises three subject areas (i) the structure and properties of the K-casein surface layer in casein micelles (ii) the properties of the protein fraction in homogenized milks (i.e. basically intact casein micelles adsorbed at fat-water interfaces) (iii) the properties of caseinate and individual caseins adsorbed at the interfaces. In this, we are at present less... 

Studies of typical nanomaterials (soil mineral components, adsorbents, silica gels with deposited proteins, so called smart surfaces, latexes, synthetic zeolites modified by ions, MCM-41 molecular sieves) were made earlier by the author of this chapter [11-17]. At present our research focuses on studies of surface properties (e.g. adsorption capacity), total heterogeneity (energetic and geometrical) of surface layers, as well as structures and phase transformations of... 

The current opinion, widely held, is that all biological membranes, including mammalian plasma membranes, have as a structural framework a phospholipid bilayer of which the characteristic feature is a parallel array of hydrocarbon chains, averaging 16 carbon atoms in length. This bilayer has some of the properties of a two-dimensional fluid in which individual lipid molecules can diffuse rapidly in the plane of their own monolayer, but cannot easily pass into the other monolayer. This lipid matrix provides the basic structure of the membrane. Whereas some protein molecules cover part of the membrane, particularly its outer surface, other protein strands penetrate the lipid layer, every here and there, and some of these strands are bunched together to form water-filled tubes or pores (Wallach and Zahler, 1966). These proteins are responsible for most of the membrane s functions, e.g. receiving and transduc-... 

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