Membrane anchoring

Glomset, J. A., Gelb, M. H., and Farnswordi, C. C., 1990. Prenyl proteins in eukaryotic cells A new type of membrane anchor. Trends in Biochemical Sciences 15 139—142. 

FIGURE 15.21 Hormone (H) binding to its receptor (R) creates a hormone receptor complex (H R) that catalyzes GDP-GTP exchange on the o -subunit of the heterotrimer G protein (G ), replacing GDP with GTP. The G -subunit with GTP bound dissociates from the /37-subunits and binds to adenylyl cyclase (AC). AC becomes active upon association with G GTP and catalyzes the formation of cAMP from ATP. With time, the intrinsic GTPase activity of the G -subunit hydrolyzes the bound GTP, forming GDP this leads to dissociation of G GDP from AC, reassociation of G with the /Sy subunits, and cessation of AC activity. AC and the hormone receptor H are integral plasma membrane proteins G and G are membrane-anchored proteins. 

Hydrophobic-tailed tetramers Abundant form in the mammalian CNS. Anchored to plasma membranes by a hydrophobic, 20 kDalton length polypeptide subunit named PRiMA (Proline-Rich Membrane Anchor). 

Why should contact between shrunken cells be damaging One possibility is that the contacts induce damaging membrane-membrane fusion, for close contact between shnmken cells has been found to induce membrane fusion above 0 °C. Moreover, freezing has been shown to induce fusion in model membranes (Anchor-doguy et al., 1987) and to produce changes in fungal hyphae that are symptomatic of fusion (Fujikawa and Miura, 1986). 

Fusion maC46 Membrane-anchored antiviral HlV-1 Egelhofer et al, 2004 HUdinger... 

Secreted neutralizing human mab 2F5 Membrane-anchored anti-gp41 scFv ... 

Melikyan GB, Egelhofer M, von Laer D (2006) Membrane-anchored inhibitory peptides capture human immunodeficiency virus type 1 gp41 conformations that engage the target membrane prior to fusion, J Virol 80 3249-3258... 

Rieske proteins are constituents of the be complexes that are hydro-quinone-oxidizing multisubunit membrane proteins. All be complexes, that is, bci complexes in mitochondria and bacteria, b f complexes in chloroplasts, and corresponding complexes in menaquinone-oxidizing bacteria, contain three subunits cytochrome b (cytochrome 6e in b f complexes), cytochrome Ci (cytochrome f in b(,f complexes), and the Rieske iron sulfur protein. Cytochrome 6 is a membrane protein, whereas the Rieske protein, cytochrome Ci, and cytochrome f consist of water-soluble catalytic domains that are bound to cytochrome b through a membrane anchor. In Rieske proteins, the membrane anchor can be identified as an N-terminal hydrophobic sequence (13). 

In be complexes bci complexes of mitochondria and bacteria and b f complexes of chloroplasts), the catalytic domain of the Rieske protein corresponding to the isolated water-soluble fragments that have been crystallized is anchored to the rest of the complex (in particular, cytochrome b) by a long (37 residues in bovine heart bci complex) transmembrane helix acting as a membrane anchor (41, 42). The great length of the transmembrane helix is due to the fact that the helix stretches across the bci complex dimer and that the catalytic domain of the Rieske protein is swapped between the monomers, that is, the transmembrane helix interacts with one monomer and the catalytic domain with the other monomer. The connection between the membrane anchor and the catalytic domain is formed by a 12-residue flexible linker that allows for movement of the catalytic domain during the turnover of the enzyme (Fig. 8a see Section VII). Three different positional states of the catalytic domain of the Rieske protein have been observed in different crystal forms (Fig. 8b) (41, 42) ... 

The Rieske protein II (SoxF) from Sulfolobus acidocaldarius, which is part, not of a bci or b f complex, but of the SoxM oxidase complex 18), could be expressed in E. coli, both in a full-length form containing the membrane anchor and in truncated water-soluble forms 111). In contrast to the results reported for the Rieske protein from Rhodobacter sphaeroides, the Rieske cluster was more efficiently inserted into the truncated soluble forms of the protein. Incorporation of the cluster was increased threefold when the E. coli cells were subject to a heat shock (42°C for 30 min) before induction of the expression of the Rieske protein, indicating that chaperonins facilitate the correct folding of the soluble form of SoxF. The iron content of the purified soluble SoxF variant was calculated as 1.5 mol Fe/mol protein the cluster showed g values very close to those observed in the SoxM complex and a redox potential of E° = +375 mV 111). 

Pan Y, Lloyd C, Zhou H et al (1997) Neurotactin, a membrane-anchored chemokine upregulated in brain inflammation. Nature 387 611-617... 

The secondary leachate collection system is accessed by collection standpipes that must penetrate the primary liner. There are two methods of making these penetrations rigid or flexible. In the rigid penetrations, concrete anchor blocks are set behind the pipe with the membranes anchored to the concrete. Flexible penetrations are preferred since these allow the pipe to move without damaging the liner. In either case, standpipes should not be welded to the liners. If a vehicle hits a pipe, there is a high potential for creating major tears in the liner at depth. 

Of the integral membrane proteins referred to above, Hll has a distinct transmembrane region (Smith et al, 1997), the GA1 proteins are anchored via a glycosylinositolphospholipid (GPI) membrane anchor on p52, with p46 being held in place by as yet undefined interactions (Jasmer et al., 1996). The P150 complex is anchored by a membrane (GPI) anchor on the 53 kDa component which forms non-covalent associations with the 45 and 53 kDa components (Rocha and Munn, 1997). The means by which... 

Another potential source of iron, at least for hepatocytes, is receptor-independent uptake of iron from transferrin. This appears to involve an iron uptake pathway from transferrin which is neither suppressed in hepatocytes by antibodies to TfR (Trinder et at, 1988), nor by transfection of HuH-7 hepatoma cells with transferrin receptor anti-sense cDNA (Trinder etat, 1996). The same pathway may also be utilized for iron uptake from isolated transferrin N-lobe, which is not recognized by the receptor (Thorstensen et at, 1995). The possible role of TfR2 in this process remains to be established, as does the physiological importance of this pathway in intact liver. Human melanoma cells (Richardson and Baker, 1994) and Chinese hamster cells lacking transferrin receptors but transfected with melanotransferrin (Kennard et at, 1995) use another pathway for transferrin iron uptake, independent of the transferrin receptor, but utilizing iron transfer from transferrin or simple iron chelates to membrane-anchored melanotransferrin, and from there onwards into the cellular interior. 

This review describes recent improvements in the measurement of the passive transport of molecules across artificial phospholipid membranes anchored inside... 

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