Transmembrane protein structures

Altenbach, C., Marti, T., Khorana, H. G., and Hubbell, W. L. (1990). Transmembrane protein structure spin labeling of bacteriorhodopsin mutants. Science 248, 1088-1092. 

C. Altenbach, T. Marti, H.G. Khorana, and W.L. Hubbell. 1990. Transmembrane protein structure Spin labeling of bacterio-rhodopsin mutants Science 248 1088-1092. (PubMed)... 

Nicotinic Acetylcholine Receptors. Nicotinic acetylcholine receptors are ligandgated ion channels whose opening is controlled by acetylcholine and nicotine agonists (196,209,210). They are transmembrane protein structures. Each receptor consists of five subunits. The structure is inserted in the plasma membrane with an aqueous channel in... 

Figure 16.5 Illustration of the structure and mechanism of the K+ channel selectivity filter with views from above (left side) and as transmembrane protein structure with a gate, central cavity, and a selectivity filter (right side). To pass through the filter, the K+ needs to be dehydrated. The K+ selectivity filter holds and stabilizes four dehydrated K+ ions by using carbonyl oxygen atoms (red) that resemble the K+ hydration shell. The smaller Na+ ion cannot stabilize in this structure that fits uniquely to the size of the K+ ions only. Based on MacKinnon s X-ray crystallographic studies and proposed mechanism.

Pakula, A., and Simon, M. (1992). Determination of Transmembrane Protein Structure by Disulfide Cross-linking The E. coli Tar Receptor, Proc. Natl. Acad. Sci. USA 89 4144—4148. 

FIGURE 9.31 The known proteoglycans include a variety of structures. The carbohydrate groups of proteoglycans are predominantly glycosaminoglycans O-linked to serine residues. Proteoglycans include both soluble proteins and integral transmembrane proteins. 

Most ABC-transporters, especially those located in the plasma membrane, are phosphorylated and glycosylated transmembrane proteins of different molecular weights (e.g., P-gp 170 kDa MRP2 190 kDa BCRP 72 kDa). Topologically, most ABC-transporter show a similar structure they are organized in two transmembrane domains (TMD), each consisting of six... 

The three selectins are related both structurally and functionally. They are transmembrane proteins, with an N-terminal C-type actin domain, followed by an EGF repeat and a variable number of complement control protein (CCP) domains. Selectins bind carbohydrates, which are present in various glycoproteins. 

Figure 41-7. The fluid mosaic model of membrane structure. The membrane consists of a bimolecu-lar lipid layer with proteins inserted in it or bound to either surface. Integral membrane proteins are firmly embedded in the lipid layers. Some of these proteins completely span the bilayer and are called transmembrane proteins, while others are embedded in either the outer or inner leaflet of the lipid bilayer. Loosely bound to the outer or inner surface of the membrane are the peripheral proteins. Many of the proteins and lipids have externally exposed oligosaccharide chains. (Reproduced, with permission, from Junqueira LC, Carneiro J Basic Histology. Text Atlas, 10th ed. McGraw-Hill, 2003.)...

Except for its narrow specificity, the ATRI gene product shares a number of properties with the higher eukaryotic MDR proteins responsible for multidrug resistance in tumour cells. The MDR gene products are also transmembrane proteins which seem to function as ATP-dependent drug-efflux pumps pumping out a variety of structurally unrelated compounds (see [25,26]). 

The artificial lipid bilayer is often prepared via the vesicle-fusion method [8]. In the vesicle fusion process, immersing a solid substrate in a vesicle dispersion solution induces adsorption and rupture of the vesicles on the substrate, which yields a planar and continuous lipid bilayer structure (Figure 13.1) [9]. The Langmuir-Blodgett transfer process is also a useful method [10]. These artificial lipid bilayers can support various biomolecules [11-16]. However, we have to take care because some transmembrane proteins incorporated in these artificial lipid bilayers interact directly with the substrate surface due to a lack of sufficient space between the bilayer and the substrate. This alters the native properties of the proteins and prohibits free diffusion in the lipid bilayer [17[. To avoid this undesirable situation, polymer-supported bilayers [7, 18, 19] or tethered bilayers [20, 21] are used. 

The photosynthetic reaction center (RC) of purple nonsulfur bacteria is the core molecular assembly, located in a membrane of the bacteria, that initiates a series of electron transfer reactions subsequent to energy transfer events. The bacterial photosynthetic RCs have been characterized in more detail, both structurally and functionally, than have other transmembrane protein complexes [1-52]. 

This was the first transmembrane protein to have its structure described in detail by Deisenhofer, Huber and Michel in 1984. They received the Nobel Prize for Chemistry 4 years later. 

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