Membrane proteins roles

Rotin, D., 0. Staub, and R. Haguenauer-Tsapis. Ubiquitination and endocytosis of plasma membrane proteins role of Nedd4/Rsp5p family of ubiquitin-protein ligases. J Membr Biol. 176 1-17.2000. 

Javadpour, M. M., Eilers, M., Groesbeek, M., and Smith, S. O. (1999). Helix packing in polytopic membrane proteins role of glycine in transmembrane helix association. Biophys. J. 77, 1609-1618. 

Nilsson, I. and von Heijne, G., Fine-tuning the topology of a polytopic membrane protein role of positively and negatively charged amino acids. Cell 62 (1990) 1135-1141. 

All the long-range forces discussed in this chapter play a role in biological processes. Interactions between membranes, proteins, ligands, antibodies... 

In subsequent studies attempting to find a correlation of physicochemical properties and antimicrobial activity, other parameters have been employed, such as Hammett O values, electronic distribution calculated by molecular orbital methods, spectral characteristics, and hydrophobicity constants. No new insight on the role of physiochemical properties of the sulfonamides has resulted. Acid dissociation appears to play a predominant role, since it affects aqueous solubiUty, partition coefficient and transport across membranes, protein binding, tubular secretion, and reabsorption in the kidneys. An exhaustive discussion of these studies has been provided (10). 

Aquaporins (AQP) are a family of integral membrane proteins expressed in all organisms and play a fundamental role in the regulation of water transport into and out of cells. 

K Channels belong to a class of membrane proteins that form highly K-selective pores in membranes. All known K Channels are composed of several (usually four) pore forming alpha subunits and auxiliary beta subunits. K Channels play an essential role in cellular excitability, being involved in repolarization of Action Potentials and setting the cell resting potential as well as contributing to potassium homeostasis. 

Souza-Schorey C, Chavrier P (2006) ARF proteins roles in membrane traffic and beyond. Nat Rev Mol Cell Biol 7 347-358... 

The 3 subunits ((31 -(34) are membrane proteins with a single transmembrane domain and an extracellular immunoglobulin-like motif, and perform the regulatory roles of the sodium channel. The (31 subunit accelerates the activation and inactivation kinetics. The (32 subunit is covalently linked to the a subunit, and is necessary for the efficient assembly of the channel. The more recently identified (33 subunit is homologous to (31, but differs in its distribution within the brain and in a weaker accelerating property. The (34 subunit is similar to (32 and is covalently linked to the a subunit. 

While the fluid mosaic model of membrane stmcture has stood up well to detailed scrutiny, additional features of membrane structure and function are constantly emerging. Two structures of particular current interest, located in surface membranes, are tipid rafts and caveolae. The former are dynamic areas of the exo-plasmic leaflet of the lipid bilayer enriched in cholesterol and sphingolipids they are involved in signal transduction and possibly other processes. Caveolae may derive from lipid rafts. Many if not all of them contain the protein caveolin-1, which may be involved in their formation from rafts. Caveolae are observable by electron microscopy as flask-shaped indentations of the cell membrane. Proteins detected in caveolae include various components of the signal-transduction system (eg, the insutin receptor and some G proteins), the folate receptor, and endothetial nitric oxide synthase (eNOS). Caveolae and lipid rafts are active areas of research, and ideas concerning them and their possible roles in various diseases are rapidly evolving. 

Rhodopsin is a seven ot-helix trans-membrane protein and visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In this photoreceptor, retinal is the chromophore bound by opsin protein, covalently linked to Lys296 by a Schiff base linkage. Kpega et al.64 have studied NMR spectra of Schiff bases being derivatives of all-frans retinal and amino-p-cyclodextrins as a model of rhodopsin, where p-cyclodextrin plays a role of a binding pocket. On the basis of analysis of the chemical shift differences for the model compound in the presence and in the absence of adamantane carboxylate, it has been shown that the derivative of 3-amino-p-cyclodextrin forms dimer in water and retinoid is inserted into p-cyclodextrin cavity [31]. 

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