Anthony Watts

University of Oxford, Biochemistry, Faculty Member

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Papers by Anthony Watts

Spin-label studies of lipid-protein interactions with reconstituted band 3, the human erythrocyte chloride-bicarbonate exchanger

Biochemistry and Cell Biology, Jan 24, 2011

Lipid-protein interactions in (Na+,K+)-ATPase-rich membranes from the rectal gland of Squalus aca... more Lipid-protein interactions in (Na+,K+)-ATPase-rich membranes from the rectal gland of Squalus acanthias have been studied by using spin-labeled lipids in conjunction with electron spin resonance (ESR) spectroscopy. Lipid-protein associations are revealed by the presence of a second component in the ESR spectra of the membranes in addition to a component which corresponds very closely to the ESR spectra obtained from dispersions of the extracted membrane lipids. This second component corresponds to spin-labeled lipids whose motion is very significantly restricted relative to that of the fluid lipids in the membrane or the lipid extract. A stoichiometry of approximately 66 lipids per 265 000-dalton protein is found for the motionally restricted component of those spin-labeled lipids (e.g., phosphatidylcholine) which show least specificity for the protein. This corresponds approximately to the number of lipids which may be accommodated within the first shell around the alpha 2 beta 2 protein dimer. A selectivity of the various spin-labeled lipids for the motionally restricted component associated with the protein is found in the following order: cardiolipin greater than phosphatidylserine approximately stearic acid greater than or equal to phosphatidic acid greater than phosphatidylglycerol approximately phosphatidylcholine approximately phosphatidylethanolamine approximately androstanol.

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Lipid-lipid and lipid-protein interactions in chromaffin granule membranesA spin label ESR study

Bba Biomembranes, 1980

The ESR spectra of six different positional isomers of a stearic acid and three of a phosphatidyl... more The ESR spectra of six different positional isomers of a stearic acid and three of a phosphatidylcholine spin label have been studied as a function of temperature in chromaffin granule membranes from the bovine adrenal medulla, and in bilayers formed by aqueous dispersion of the extracted membrane lipids. Only minor differences were found between the spectra of the membranes and the extracted lipid, indicating that the major portion of the membrane lipid is organized in a bilayer arrangement which is relatively unperturbed by the presence of the membrane protein. The order parameter profile of the spin label lipid chain motion is less steep over the first half of the chain than over the section toward the terminal methyl end of the chain. This &#39;stiffening&#39; effect is attributed to the high proportion of cholesterol in the membrane and becomes less marked as the temperature is raised. The isotropic hyperfine splitting factors of the various positional isomers display a profile of decreasing polarity as one penetrates further into the interior of the membrane. No marked differences are observed between the effective polarities in the intact membranes and in bilayers of the extracted membrane lipids. The previously observed temperature-induced structural change occurring in the membranes at approx. 35 degrees C was found also in the extracted lipid bilayers, showing this to be a result of lipid-lipid interactions and not lipid-protein interactions in the membrane. A steroid spin label indicated a second temperature-dependent structural change occurring in the lipid bilayers at lower temperatures. This correspond to the onset of a more rapid rotation about the long axis of the lipid molecules at a temperature of approx. 10 degrees C. The lipid bilayer regions probed by the spin labels used in this study may be involved in the fusion of the chromaffin granule membrane leading to hormone release by exocytosis.

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Probing Membrane Surfaces and the Location of Membrane-Embedded Peptides by 13C MAS NMR Using Lanthanide Ions

J Magn Reson, 1999

A simple but efficient 13C MAS NMR method is presented for the determination of the location of e... more A simple but efficient 13C MAS NMR method is presented for the determination of the location of embedded molecules such as peptides relative to biological membrane surfaces by exploiting the interaction with paramagnetic lanthanide ions. Using various aqueous Dy3+ concentrations a distance-dependent differential paramagnetic quenching of NMR lipid resonance intensities for specific carbon sites was observed, with residues at the bilayer surface quenched effectively and hydrophobic sites unaffected by Dy3+. Tested on the membrane-embedded 50 residue long M13 coat protein, 13C labeled at its Val-29 and Val-31 residues, no paramagnetic quenching was observed for the peptide resonances by Dy3+, suggesting that Val-29 and Val-31 are not in close proximity to the bilayer interface, but buried deeply inside the hydrophobic region of the lipid bilayer.

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Structure determination of the cyclohexene ring of retinal in bacteriorhodopsin by solid-state deuterium NMR

Biochemistry Usa, Nov 1, 1992

The orientation and conformation of retinal within bacteriorhodopsin of the purple membrane of Ha... more The orientation and conformation of retinal within bacteriorhodopsin of the purple membrane of Halobacterium halobium was established by solid-state deuterium N M R spectroscopy, through the determination of individual chemical bond vectors. The chromophore ([2,4,4,16,16,16,17,17,17,18,18-2H1 I]retinal) was specifically deuterium-labeled on the cyclohexene ring and incorporated into the protein. Auniaxially oriented sample of purple membrane patches was prepared and measured at a series of inclinations relative to the spectrometer field. 31P N M R was used to characterize the mosaic spread of the oriented sample, and computer simulations were applied in the analysis of the *H N M R and 31P N M R spectral line shapes. From the deuterium quadrupole splittings, the specific orientations of the three labeled methyl groups on the cyclohexene ring could be calculated. The two adjacent methyl groups (on CI) of the retinal were found to lie approximately horizontal in the membrane and make respective angles of 94" f 2" and 7 5 O f 2 O with the membrane normal. The third group (on C,) points toward the cytoplasmic side with

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Engineered bacteriorhodopsin: a molecular scale conductance photoswitch

Bacteriorhodopsin, BR, is a natural, photoresponsive, biomolecule that has potential application ... more Bacteriorhodopsin, BR, is a natural, photoresponsive, biomolecule that has potential application in data storage, imaging and sensing. Being membrane-bound, however, it is coupled with metallic electronic surfaces only with some difficulty. We report herein a facile method to generate uniformly orientated, anchored and active monolayers of BR on metallic electrodes. In the present study, the cytoplasmic side of the BR is equipped with an engineered cysteine to achieve largely lipid-free, orientation-specific, highly stable, covalent immobilization on gold surfaces. By using non-invasive Kelvin probe force microscopy, it is possible to measure the light-induced proton accumulation at the extracellular protein surface at truly molecular scales. The intimate probe-BR interaction possible on lipid removal facilitates the detection of photoinduced surface potential switching substantially larger ((20.4 ± 7.5) mV) with functional single delipidated mutant BR trimers than for the wild-type protein. The proton pumping detected is also notably highly unidirectional with the orientated protein.

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The Role of IGF-Binding Proteins in Mediating the Effects of Recombinant Human IGF-I on Insulin Requirements in Type 1 Diabetes Mellitus

To determine the role of IGF-binding proteins in mediating the direct effects of recombinant huma... more To determine the role of IGF-binding proteins in mediating the direct effects of recombinant human IGF-I on insulin requirements in type 1(insulin-dependent) diabetes mellitus, overnight changes in IGF-I, IGF-II, and IGF-binding protein-1, -2, and -3, collected under euglycemic conditions, were compared in nine subjects after double blind, randomized, sc administration of recombinant human IGF-I (40 g/kg) or placebo at 1800 h. On both nights a somatostatin analog infusion (300 ng/kg⅐h) suppressed endogenous GH production, and three timed discrete GH pulses (total, 0.029 IU/kg⅐night) ensured identical GH levels.

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Charge effects of protein interactions at lipid-water interface probedby H-2 NMR

Protein is the most important emulsion stabilizer from the Food Science point of view and its ori... more Protein is the most important emulsion stabilizer from the Food Science point of view and its original structure and unfolding of the protein at the interface is of paramount importance for emulsion stability. Many different approaches have been taken to gathering more information about the emulsion phenomenon, but most of them result physical, interfacial or even empirical information about this process.&amp;amp;amp;#x27;Molecular aspects of the lipid-protein interaction at the water-oil interface is scarce and often difficult to obtain. Microscopic, ...

Debris Avalanche Deposits on the Flanks of the Canary Islands: Contrasts Between El Hierro and Tenerife

Electrostatic and Hydrophobic Contributions to the Folding Mechanism of Apocytochrome c Driven by the Interaction with Lipid †

Biochemistry Usa, Oct 1, 1998

In aqueous solution, while cytochrome c is a stably folded protein with a tightly packed structur... more In aqueous solution, while cytochrome c is a stably folded protein with a tightly packed structure at the secondary and tertiary levels, its heme-free precursor, apocytochrome c, shows all features of a structureless random coil. However, upon interaction with phospholipid vesicles or lysophospholipid micelles, apocytochrome c undergoes a conformational transition from its random coil in solution to an R-helical structure on association with lipid. The driving forces of this lipid-induced folding process of apocytochrome c were investigated for the interaction with various phospholipids and lysophospholipids. Binding of apocytochrome c to negatively charged phospholipid vesicles induced a partially folded state with ∼85% of the R-helical structure of cytochrome c in solution. In contrast, in the presence of zwitterionic phospholipid vesicles, apocytochrome c remains a random coil, suggesting that negatively charged phospholipid headgroups play an important role in the mechanism of lipid-induced folding of apocytochrome c. However, negatively charged lysophospholipid micelles induce a higher content of R-helical structure than equivalent negatively charged diacylphospholipids in bilayers, reaching 100% of the R-helix content of cytochrome c in solution. Furthermore, micelles of lysolipids with the same zwitterionic headgroup of phospholipid bilayer vesicles induce ∼60% of the R-helix content of cytochrome c in solution. On the basis of these results, we propose a mechanism for the folding of apocytochrome c induced by the interaction with lipid, which accounts for both electrostatic and hydrophobic contributions. Electrostatic lipidprotein interactions appear to direct the polypeptide to the micelle or vesicle surface and to induce an early partially folded state on the membrane surface. Hydrophobic interactions between nonpolar residues in the protein and the hydrophobic core of the lipid bilayer stabilize and extend the secondary structure upon membrane insertion.

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Spin label ESR of bacteriophage M13 coat protein in mixed lipid bilayers. Determination of number of binding sites and exchange parameters

Biochemistry Usa, 1989

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Solid-state NMR approaches for studying the interaction of peptides and proteins with membranes1

Biochimica Et Biophysica Acta Mr Reviews on Biomembranes, Dec 1, 1998

1. Biochim Biophys Acta. 1998 Nov 10;1376(3):297-318. Solid-state NMR approaches for studying the... more 1. Biochim Biophys Acta. 1998 Nov 10;1376(3):297-318. Solid-state NMR approaches for studying the interaction of peptides and proteins with membranes. Watts A. Biomembrane Structure Unit, Biochemistry Department, Oxford University, Oxford OX1 3QU, UK. awatts@bioch.ox.ac.uk. PMID: 9804977 [PubMed - indexed for MEDLINE]. Publication Types: Research Support, Non-US Gov&amp;amp;#x27;t; Review. MeSH Terms. Animals; Cytochrome c Group/chemistry; ...

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Lithosphere age controls structural styles or patterns of shortening in collision belts

ABSTRACT Continental deformation is known to preferentially focus in young tectonic provinces, wh... more ABSTRACT Continental deformation is known to preferentially focus in young tectonic provinces, where the lithosphere has been weakened during previous subduction, rifting and orogenic events1-3. This suggests that pre-existing thermo-mechanical properties and composition of the crust and mantle lithosphere may control the structural styles that develop in collisional orogens. Although long-term crustal shortening is now fairly well quantified in a number of external zones of orogens, the reasons for the differences in crustal-scale deformation in these settings has rarely been addressed4,5. Here, we examine the relationship between long-term crustal shortening in collisional orogens that have developed on lithospheres of different thermo-tectonic age and proxies of long-term lithosphere strength. By analyzing more than 50 data sets from 30 fold and thrust belts, we show that shortening and thermotectonic age at time of shortening are correlated. In particular, deformation of Phanerozoic lithosphere, characterized by low elastic thickness (~20 km), high lithospheric temperature and fertile, weak, instable mantle is prone to involve mid-crustal detachment, thus reducing bulk crustal strain (&lt;35%). Older cratonic blocks, characterized by higher elastic thickness (&gt;60 km) and high-viscosity mantle promote stable underthrusting characterized by higher, more localized, shortening (up to ~70%) in weakly consolidated sediments. Our findings provide a key for linking distribution of continental deformation with secular cooling of the Earth and inherited properties of the lithosphere, including the nature of the sub-continental mantle and thermo-mechanical structure of the crust.

The long-term strength of continental lithosphere: "Jelly sandwich" or "crème brûlée"?

Gsa Today, 2006

There has been much debate recently concern ing the long-term (i.e., >1 m.y.) strength of contine... more There has been much debate recently concern ing the long-term (i.e., >1 m.y.) strength of continen tal lithosphere. In one model, dubbed jelly sandwich, the strength resides in the crust and mantle, while in another, dubbed crème brûlée, the mantle is weak and the strength is limited to the crust. The different models have arisen because of conflicting results from elastic thickness and earthquake data. We address the problem here by first reviewing elastic thickness estimates and their relationship to the seismogenic layer thickness. We then explore, by numerical thermomechanical model ing, the implications of a weak and strong mantle for structural styles. We argue that, irrespective of the actual crustal strength, the crème-brûlée model is unable to explain either the persistence of mountain ranges or the integrity of the downgoing slab in collisional systems. We conclude that while the crème-brûlée model may apply in some tectonic settings, a more widely applica ble model is the jelly sandwich.

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Discussion on subsidence history of the north Indian continental margin, Zanskar-Ladakh Himalaya, NW India Journal, Vol. 162, 2005, pp. 135-146

Journal of The Geological Society, 2005

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The study of single biological and model membranes via small-angle neutron scattering

Progress in Colloid & Polymer Science, 1993

In this work we return to the possible uses of small-angle neutron scattering (SANS) in the study... more In this work we return to the possible uses of small-angle neutron scattering (SANS) in the study of single membrane structure in water solutions at low membrane concentrations (ie, in excess water).—Using the example of lipid vesicles the effectiveness of this method in the determination of membrane thickness will be shown and the limits within which this method can be used with the same aims will be set.—Most important is the fact that the use of SANS on single membranes in solution makes possible to determine the position of molecular ...

Expression of isotopically labelled membrane transport proteins

Biochemical Society Transactions, 1999

Home. Bioenergetics and Metabolism; Cell Biology; Development and Disease; Genes; Molecular Struc... more Home. Bioenergetics and Metabolism; Cell Biology; Development and Disease; Genes; Molecular Structure and Function; Signal Transduction. About: Mission statement; Aims and scope; Honorary Editor; Advisory Panel; COPE; News; Portland Press: Biochemical Journal: Current Issue; Reviews. Clinical Science. Contact; Terms and conditions of usage; Rights and permissions; Disclaimer. Gateways: Bioenergetics and Metabolism; Cell Biology; Development ...