Trans-membrane channels

Just as there are cation channels, there are also trans-membrane channels involved in the transport of biologically important anions such as Cl-. The crystal structure of the CIC chloride channel from Salmonella typhimurium was reported in 2002.3 Along with the determination of the Streptomyces lividans potassium channel structure, this work won a share of the 2003 Nobel prize in chemistry for Roderick MacKinnon (Howard Hughes Medical Institute, New York, USA). Chloride channels catalyse the flow of chloride across cell membranes and play a significant role in functions such as... 

Cragg, P. J., Allen, M. C., Steed, J. W., A toothpaste tube model for ion transport through trans- membrane channels. 

The neuroactive agents from widow spiders are called a-latrotoxins they appear to form trans-membrane channels and usually have high molecular weights ( 130,000). They cause massive release of neurotransmitters as they stimulate fusion of the S maptic vesicles (which contain neurotransmitters) with the pre-synaptic membrane. The Australian red back spider often bites people who are in bed or asleep and the venom has a long-term effect, with patients recovering partially and then collapsing with further pain, numbness of an affected limb and even paralysis, still being affected two months later. Studies have shown that... 

Kimaro et al. [93] had prepared free-standing membranes by thermally initiated cross-linking copolymerization of styrene monomers followed by leaching of a polyester present as pore former at a concentration of 1.8 wt% in the reaction mixture. SEM pictures suggested the presence of isolated pores with diameters of up to 1 pm at a low density (< 2 %). In line with permeation data, it could be speculated that trans-membrane channels had been obtained, induced by the presence of a removable macromolecular pore former in the reaction mixture. 

Fig. 22. The Fox and Richards model of the alamethicin trans-membrane channel shown diagrammatically. Interruption of the a-helical hydrogen bonding by the Pro-14 residue is signified by representation of each monomer as two cylindrical sections. The stippled spheres at the mouth of the channel represent the Glu-18, the spheres at the centre the Gln-7, and the spheres at the top the Gln-19 residues. Fox, R. O., Richards, F. M. Reprinted by permission from Nature 300, 325 (1982). Copyright Macmillan Journals Limited...

IV. Ca2+ in lonophores, Channels, and Pumps A. Trans-Membrane Transport... 

Fig. 5.1 Schematic drawing of membrane association modes of peptides A Integral membrane proteins (1) major fd coat protein gpVIII of bacteriophage Ml 3 (pdb lfdm), anchored by an 18-residue trans-membrane hydrophobic helix (2) bovine rhodopsin, a 7 trans-membrane domain (G-protein-coupled) receptor (pdb lf88) (3) ion channel peptaibol Chrysospermin C (pdb lee7), and B Peripheral membrane proteins (1) neuro-...

The delta opioid receptor is a member of the large family of seven trans-membrane-spanning G protein-coupled receptors (GPCRs), as discussed extensively in Chapter 2. Delta opioid receptors modulate many intracellular effectors through their activation of GTP-binding proteins (G proteins), including adenylyl cyclase, K+ channels, Ca2+ channels, the MAP kinase cascade, phospholipase C, and intracellular Ca2+ release [1] (see Chap. 5). 

Some peptide antibiotics act as trans-membrane ion channels. Vibrational spectroscopy shows that ionophores, such as gramicidin A, valinomycin, nystatin, and amphotericins, interact with phospholipid bilayers (Susi et al., 1979). 

Hu J, Asbury T, Achuthan S, Li C, Bertram R, Quine JR, Fu R, Cross TA. Backbone structure of the amantadine-blocked trans-membrane domain M2 proton channel from Influenza A virus. Biophys. J. 2007 92 4335-4343. 

Park SH, Mrse AA, Nevzorov AA, Mesleh MF, Oblatt-Montal M, Montal M, Opella SJ. Three-dimensional structure of the channel-forming trans-membrane domain of virus protein u (Vpu) from HIV-L J. Mol. Biol. 2003 333 409-424. 

Electron microscopy studies have revealed that, like acetylcholine receptors, the ion channel of the GABA receptor is formed by the pentameric assembly of hetero-oligomeric subunits (129) each subunit has four trans-membrane spanning domains and all five sub-uinits are arranged so that their second transmembrane domains comprise the ion channel wall. Cloning of the subunits from vertebrates has resulted in nearly 20 cDNAs, which have... 

Perhaps the most recent dramatic advance has been the determination of the three-dimensional structure of a bacterial channel from S. lividans (Doyle et al., 1998). This channel is composed of four identical subunits, each with two trans-membrane sequences and a pore region, that associate in tepee shape to form the functional ion channel containing within it the selectivity filter that discriminates from other ions. The selectivity filter contains a so-called signature sequence, highly conserved residues that characterize ion channels and the Gly-Tyr-Gly components of this sequence in the four subunits bind through their carbonyl residues and are responsible for the ionic selectivity of the channel. 

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