Protein/membrane interaction

Peptides may bind to a membrane either by association to its surface or by insertion into its interior. The latter class comprises the integral membrane proteins whose structures are largely a-helical or / -barrel type (see Chap. 12 in Ref. [32]). The topology of interaction of helices with membranes is displayed in Fig. 5.1. 

An important question arises about the effects of phospholipid composition and the function of membrane-bound enzymes. The phospholipid composition and cholesterol content in cell membranes of cultured cells can be modified, either by supplementing the medium with specific lipids or by incubation with different types of liposomes. Direct effects of phospholipid structure have been observed on the activity of the Ca2+-ATPase (due to changes in the phosphorylation and nucleotide binding domains) [37]. Evidence of a relationship between lipid structure and membrane functions also comes from studies with the insulin receptor [38]. Lipid alteration had no influence on insulin binding, but modified the kinetics of receptor autophosphorylation. 

Protein binding to lipids also results in ordering of lipids. However, the effect is short-range, basically including only the first shell of phospholipids around the protein [39]. In- 

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Membrane Processes Membrane processes are also used diafiltration is convenient for the removal of small contaminating species such as salts and smaller proteins, and can be combined with subsequent steps to concentrate the protein. Provided that proper membrane materials have been selected to avoid protein-membrane interactions, diafiltration using ultrafiltration membranes is typically straightforward, high-yielding and capital-sparing. These operations can often tolerate the concentration or the desired protein to its solu-bihty limit, maximizing process efficiency. 

Majd, S. and Mayer, M. (2005) Hydrogel stamping of arrays of supported lipid bilayers with various lipid compositions for the screening of drug-membrane and protein-membrane interactions. Angew. Chem. Int. Ed., 44, 6697-6700. 

McLaughlin, S., and Aderem, A. (1995). The myristoyl-electrostatic switch a modulator of reversible protein-membrane interactions. Trends Biochem. Sci. 20, 272—276. 

The ability to biosynthetically incorporate noncoded amino acids into proteins site-specifically has facilitated studies not previously possible. These include studies of protein stability, the initiation of protein translation, electron transfer, protein-protein and protein-membrane interactions, reversal of enzyme substrate specificity, and structure-function relationships, among others. A growing number of research labs have begun to report applications of this technique. A brief look at some recent applications of the suppression mutagenesis technique follows. 

Selected entries from Methods in Enzymology [vol, page(s)] . Applications, 246, 335 [immunoassay, 246, 343-344 nucleic acids, 246, 344-345 photoreceptors, 246, 341-343 protein conformation, 246, 339-340 protein-membrane interactions, 246, 340-341 two-dimensional imaging, 246, 345] energy level diagram, 246, 336 excited state decay kinetics, 246, 337-338 in-... 

In vacuo simulations do not correctly reproduce protein-membrane interactions, and hence should be avoided in modeling membrane proteins. 

The structural element of PARK that interacts specifically with the Py-complex is localized in the C-terminal third of the PARK seqimce (Inglese et al., 1994). It possesses the characteristics of an independently folding protein domain and is ranked with the pleckstrin homology domains (PH domains). The PH domains are protein modules (see Chapter 8), foimd in many proteins, that by binding of inositol lipids (see Chapter 6) mediate protein-membrane interactions. 

The spectrin family of proteins, depending on the particular function, has numerous smaller motifs and binding sites for interaction with other proteins. These regions are important, as they are major protein-protein or protein-membrane interaction modules that bind to F-actin, proline-containing ligands, and/or phospholipids. Spectrin and dystrophin/utro-phin have all acquired copies of such domains since their evolution from a-actinin, presumably as a consequence of their more diverse roles in the cell. 

In terms of biosensing applications using such layers, again cholera toxin detection on a porous silicon substrate [85] has been reported. Also biotin-avidin interaction by QCM [86], glutamate detection [87], as well as protein membrane interactions [88, 89] have been studied. 

The membrane of enveloped viruses makes them highly attractive structural targets in seeking a general understanding of protein-membrane interactions and membrane fusion events. Perhaps the best structural information currently available for a membrane virus has been obtained for the alphaviruses, which possess two protein layers sandwich-... 

Kinnunen PKJ. On the molecular-level mechanisms of peripheral protein-membrane interactions induced by lipids forming inverted non-lamellar phases. Chem. Phys. Lipids 1996 81 151-166. 

Huisman, I.H., Pradanos, P., and Hernandez, A., The effect of protein-protein and protein-membrane interactions on membrane fouling in ultrafiltration, J. Membr. Sci., 179, 79, 2000. 

Khelashvili, G., Harries, D., Weinstein, H. Modeling membrane deformations and lipid demixing upon protein-membrane interaction The BAR dimer adsorption. Biophys. J. 2009, 97,1626-35. 

The dipole potential of a lipid membrane is manifested between the hydrocarbon core of the membranes and the first few water molecules adjacent to the lipid head groups (Brockman, 1994). This potential is caused by the uniform orientation of the phosphocholine moiety, the carbonyl groups of the ester union, and, to some extent, by the presence of polarizable groups in the membrane hydrocarbon phase (Voglino et al., 1998 McIntosh, 2002). Therefore, in addition to steric hindrance and electrostatic forces, the hydration of the phospholipids plays a significant role in protein-membrane interactions as a participant in the short-range repulsive forces (McIntosh, 2002). 

A. channeling B. specific protein-protein interactions C. specific protein-membrane interactions D. kinetic effects E. isolation of complexes or muldfiinctiona] proteins. F. genetic evidence G. model systems H. existence of multifunctional or multienzyme proteins 1. physical chemical evidence. 

C3, the Cys988-Gln991 Z-thioester linkage may react with nucleophilic groups (mainly OH and to a lesser extent NH) at cell surfaces and proteins in order to increase internalization [12]. Thioesters also reversibly connect cysteine residues to palmitate [13] and other fatty acids [14] in order to facilitate protein-membrane interactions and protein trafficking. 

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