Exchange proteins

AE Garcia, G Hummer. Conformational dynamics of cytochrome c CoiTelation to hydrogen exchange. Proteins 36 175-191, 1999. 

Jay, D., and Candey, L., 1986. Structural a.spects of die red cell anion exchange protein. Annual Review of Biochemistry 55 511-538. 

The major proteins (which include spectrin, ankyrin, the anion exchange protein, actin, and band 4.1) have been studied intensively, and the principal features of their disposition (eg, integral or peripheral), structure, and function have been established. 

The Major Integral Proteins of the Red Blood Cell Membrane Are the Anion Exchange Protein the Glycophorins... 

The anion exchange protein (band 3) is a transmembrane glycoprotein, with its carboxyl terminal end on the external surface of the membrane and its amino terminal end on the cytoplasmic surface. It is an example of a multipass membrane protein, extending across the... 

A similar phenomenology attends the actions of maitotoxin, another large organic molecule that induces a Ca selective membrane permeability (see chapter by Ohizumi Kobayashi in this volume). None of the known inhibitors of Ca channels, including Co , Cd, dihydropyridines, and verapamil or diltiazem affect the maitotoxin-induced increase in Ca permeability. To date, an association between maitotoxin and an existing Ca pump or exchange protein has not been demonstrated. 

Next, Reilly et al. [65] localized the Na /H exchanger gene product in renal epithelial cells where the distributions of the kinetic isoforms was well-established. The strategy was based on the observation that the resistant- and sensitive-types are restricted to the apical and basolateral membranes, respectively, in confluent LLC-PK]/Clone 4 cells [8]. Thus, if proteins encoded by the cloned cDNAs localized to the apical membrane this would indicate that they represent the resistant-type. Localization to the basolateral membrane would prove they were the sensitive-type and presence on both membranes would suggest that the two functional isoforms had identical primary structures. Na exchanger proteins were localized by... 

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

The number of enzymes and functional proteins that are reportedly regulated by S-nitrosation is on the rise. For example, a search of PUBMED with the key word S-nitrosation revealed some 70 reports of in vitro regulation of enzymes, proteins and cellular processes that are affected by S-nitrosation. Some of these processes that have been well characterized include, nuclear regulatory proteins the NMDA receptor and the ertrocyte anion exchange protein 1 (AE1) (see review by Gaston, 2003). 

Y. Bai, J.S. Milne, L. Mayne and S.W. Englander, Primary structure effects on peptide group hydrogen exchange, Proteins Struct. Function Genet., 17 (1993) 75-86. 

Figure 6.4. Mode of action of low-molecular-weight G-proteins. The raslike proteins normally bind GDP, but this may be exchanged for GTP via a process that may be assisted by guanine nucleotide exchange protein (GNEP). The GTP-bound ras protein may then interact with and activate its target protein (X). The activity of GTPase activating protein (GAP) may then assist to hydrolyse GTP to GDP, to inhibit ras activity.

The method of introduction of the fluorophore into the membrane is also important. Many probes are introduced into preexisting vesicles, natural membranes, or whole cells by the injection of a small volume of organic solvent containing the fluorophore. For DPH, tetrahydrofuran is commonly used, while methanol is often employed for other probes. The amount of solvent used should be the absolute minimum possible to avoid perturbation of the lipids, since the solvent will also partition into the membrane. With lipid vesicles this potential problem can be avoided by mixing the lipids and fluorophore followed by evaporation of the solvent and codispersing in buffer. For fluorophores attached to phospholipids, this is the only way to get the fluorophore into the bilayer with natural membranes, phospholipid exchange proteins or other techniques may have to be employed. 

Burns-Hamuro L., Hamuro Y, Kim J., Sigala P., Fayos R., Stranz D., Jennings P., Taylor S., Woods V.L. Jr Distinct interaction modes of an AKAP bound to two regulatory subunit isoforms of protein kinase A revealed by amide hydrogen/ deuterium exchange. Protein Sci. 

Further examples of substrates of protein kinase C are the epidermal growth factor receptor (see Chapter 8), a Na7H exchanger protein, and Raf kinase (Chapter 9). Activation of protein kinase C may, as the examples show, act on other central signal transduction pathways of the cell it may have a regulating activity on transcription processes and it is involved in the regulation of transport processes. Many substrates of protein kinase C are membrane proteins and it is evident that membrane association of protein kinase C is of great importance for the phosphorylation of these proteins. 

The transition from inactive GDP state to active GTP state may be accelerated by proteins that cause the boimd GDP to dissociate. The guanine nucleotide exchange factors (GEF) play an essential role in signal transduction via Ras proteins. Loss of exchange activity by mutation of the exchange proteins has the same effect in lower organisms as loss of the Ras gene. 

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