ABSTRACT
Voltage-dependent K(+), Ca(2+), and Na(+) channels play vital roles in basic physiological processes, including management of the action potential, signal transduction, and secretion. They share the common function of passively transporting ions across cell membranes; thus, it would not be surprising if they should exhibit similarities of both structure and mechanism. Indeed, the principal pore-forming (alpha) subunits of each show either exact or approximate 4-fold symmetry and share a similar transmembrane topology, and all are gated by changes in membrane potential. Furthermore, these channels all possess an auxiliary polypeptide, designated the beta subunit, which plays an important role in their regulation. Despite considerable functional semblences and abilities to interact with structurally similar alpha subunits, however, there is considerable structural diversity among the beta subunits. In this review, we discuss the similarities and differences in the structures and functions of the beta subunits of the voltage-dependent K(+), Ca(2+), and Na(+) channels.
Subject(s)
Ion Channels/chemistry , Calcium Channels/chemistry , Calcium Channels/physiology , Humans , Ion Channels/physiology , Models, Molecular , Potassium Channels/chemistry , Potassium Channels/physiology , Protein Conformation , Protein Subunits , Sodium Channels/chemistry , Sodium Channels/physiologyABSTRACT
Synchrotron radiation circular dichroism (SRCD) spectroscopy is an emerging technique for sensitive determination of protein secondary structures and for monitoring of conformational changes. An important issue for its adoption as a useful technique is whether the high-intensity low-wavelength vacuum ultraviolet radiation in the SRCD chemically damages proteins. In this paper, using horse myoglobin as a test sample, it is shown that extensive irradiation in the SRCD does not produce any change in the chemical nature of the protein as detected by either SDS gel electrophoresis or mass spectrometry. In addition, no changes in the protein secondary structure are detectable from the SRCD spectra after extensive exposure to the SRCD beam.
Subject(s)
Circular Dichroism , Proteins/radiation effects , Synchrotrons , Protein Structure, Secondary/radiation effects , Ultraviolet RaysABSTRACT
An audit at the Queensway Anxiety Management Clinic of 2014 children, referred for dental treatment, showed that relative analgesia by inhalation of nitrous oxide and oxygen failed in 40% of cases successfully to complete treatment. We therefore investigated the efficacy of a new inhalation conscious sedation technique, which reduced the need for general anaesthesia. Seventy-five children aged 3-15 years were given inhalation conscious sedation, with sevoflurane 0.1-0.3% and nitrous oxide 40% in oxygen. In 69 children (92%), the dental treatment was completed successfully. Most children (93%) had recovered fully within 10 min without side-effects. Treatment was fully accepted by 88% of children and 91% of their parents. The use of sevoflurane in low concentrations to supplement nitrous oxide and oxygen for conscious sedation in children appears to be safe and effective and further study is currently in progress.
Subject(s)
Anesthesia, Dental/methods , Anesthetics, Inhalation , Conscious Sedation/methods , Methyl Ethers , Nitrous Oxide , Adolescent , Child , Child, Preschool , Dental Anxiety/etiology , Humans , Pain Measurement , Recovery of Function , Sevoflurane , Treatment OutcomeABSTRACT
The cytochrome b(5) tail is a 43-residue membrane-embedded domain that is responsible for anchoring the catalytic domain of cytochrome b(5) to the endoplasmic reticulum membrane. Different models for the structure of the membrane domain of cytochrome b(5) have been proposed, including a helical hairpin and a single transmembrane helix. In the present study, CD spectroscopy was used to investigate the conformation of the tail in different environments, and as a function of temperature, with the goal of understanding the nature of the membrane-bound conformation. Whereas residue property profiling indicates that bending of a helix in the middle of the peptide might be possible, the experimental results in small unilamellar vesicles and lysophosphatidylcholine micelles are more consistent with a single transmembrane helix. Furthermore, although there is evidence for some refolding of the polypeptide with temperature, this is not consistent with a hairpin-to-transmembrane transition. Rather, it appears to represent an increase in helical content in fluid lipid environments, perhaps involving residues at the ends of the transmembrane segment.
Subject(s)
Cell Membrane/metabolism , Cytochromes b5/chemistry , Amino Acid Sequence , Animals , Catalytic Domain , Cattle , Cell Membrane/chemistry , Circular Dichroism , Electrophoresis, Polyacrylamide Gel , Models, Biological , Molecular Sequence Data , Phospholipids/metabolism , Protein Conformation , Protein Structure, Secondary , Protein Structure, Tertiary , Sequence Homology, Amino Acid , TemperatureABSTRACT
Structure prediction methods have been used to establish a domain structure for the voltage-dependent calcium channel beta subunit, beta1b. One domain was identified from homology searches as an SH3 domain, whilst another was shown, using threading algorithms, to be similar to yeast guanylate kinase. This domain structure suggested relatedness to the membrane-associated guanylate kinase protein family, and that the N-terminal domain of the beta subunit might be similar to a PDZ domain. Three-dimensional model structures have been constructed for these three domains. The extents of the domains are consistent with functional properties and mutational assays of the subunit, and provide a basis for understanding its modulatory function.