Denaturation of proteins. III. N.M.R. studies on lysozyme and α-lactalbumin

1971 ◽  
Vol 24 (8) ◽  
pp. 1703 ◽  
Author(s):  
JH Bradbury ◽  
NLR King
Keyword(s):  
Time Scale ◽  
High Field ◽  
Measured Parameter ◽  
Methionine Residue ◽  
Aromatic Interactions ◽  
Arginine Residues ◽  
Multiple State ◽  
Proton Resonances ◽  
Denaturation Of Proteins ◽  
Denaturation Process

The denaturation process is considered with particular reference to the application of N.M.R. spectroscopy for its study. All known examples of exchange between native and unfolded states are shown to be cases of slow exchange on the N.M.R. time scale. Furthermore, providing the denaturation is two-state, the fraction of unfolded molecules α can be obtained from measurements of the heights of various N.M.R. resonances, including those which are composites of several closely related types of protons. The experimentally measured parameter F does not equal α if intermediates are present or in the very unlikely event of the denaturation process occurring rapidly on the n.m.r, time scale. Multiple-state denaturations can be observed by the non-coincidence of curves of F (determined from different resonances) against denaturant parameter or from the occurrence of proton resonances which are only observed in the transition region. ��� Lysozyme is not denatured in 8M urea at pH > 3.0. At pH 2.8 the NH resonances of arginine sharpen before those of many other proton resonances in the molecule which sharpen simultaneously. It is concluded that three clusters of arginine side-chains, which involve seven arginine residues, unfold before the bulk of the molecule. Denaturation of α-lactalbumin in urea at pH 2.5 and pH 6.0 in D2O occurs over a broad range of concentrations and is clearly multiple state at pH 6.0. ��� The N.M.R. study shows the presence of an exposed methionine residue in α-lactalbumin, no evidence of high field perturbed methyl resonances, and a considerably reduced stability to denaturation as compared with lysozyme. The dearth of aliphatic-aromatic interactions in α-lactalbumin may account for its more open structure compared with lysozyme as well as its reduced stability towards denaturation.

scholarly journals Heparin binding to platelet factor-4. An NMR and site-directed mutagenesis study: arginine residues are crucial for binding

1995 ◽  
Vol 312 (2) ◽  
pp. 357-365 ◽  
Author(s):  
K H Mayo ◽  
E Ilyina ◽  
V Roongta ◽  
M Dundas ◽  
J Joseph ◽  
...  
Keyword(s):  
Alpha Helix ◽  
Platelet Factor 4 ◽  
Site Directed Mutagenesis ◽  
Directed Mutagenesis ◽  
Heparin Binding ◽  
Nmr Studies ◽  
Platelet Factor ◽  
Binding Data ◽  
Arginine Residues ◽  
Proton Resonances

Native platelet factor-4 (PF4) is an asymmetrically associated, homo-tetrameric protein (70 residues/subunit) known for binding polysulphated glycosaminoglycans like heparin. PF4 N-terminal chimeric mutant M2 (PF4-M2), on the other hand, forms symmetric tetramers [Mayo, Roongta, Ilyina, Milius, Barker, Quinlan, La Rosa and Daly (1995) Biochemistry 34, 11399-11409] making NMR studies with this 32 kDa protein tractable. PF4-M2, moreover, binds heparin with a similar affinity to that of native PF4. NMR data presented here indicate that heparin (9000 Da cut-off) binding to PF4-M2, while not perturbing the overall structure of the protein, does perturb specific side-chain proton resonances which map to spatially related residues within a ring of positively charged side chains on the surface of tetrameric PF4-M2. Contrary to PF4-heparin binding models which centre around C-terminal alpha-helix lysines, this study indicates that a loop containing Arg-20, Arg-22, His-23 and Thr-25, as well as Lys-46 and Arg-49, are even more affected by heparin binding. Site-directed mutagenesis and heparin binding data support these NMR findings by indicating that arginines more than C-terminal lysines, are crucial to the heparin binding process.

scholarly journals A family of hyperpolarization-activated channels selective for protons

2020 ◽  
Vol 117 (24) ◽  
pp. 13783-13791 ◽  
Author(s):  
Lea Wobig ◽  
Thérèse Wolfenstetter ◽  
Sylvia Fechner ◽  
Wolfgang Bönigk ◽  
Heinz G. Körschen ◽  
...  
Keyword(s):  
Cyclic Nucleotides ◽  
Hcn Channels ◽  
Freshwater Environment ◽  
Proton Channels ◽  
Voltage Gated ◽  
Methionine Residue ◽  
Pacemaker Channels ◽  
Arginine Residues ◽  
Voltage Sensing Domain ◽  
Pore Domain

Proton (H+) channels are special: They select protons against other ions that are up to a millionfold more abundant. Only a few proton channels have been identified so far. Here, we identify a family of voltage-gated “pacemaker” channels, HCNL1, that are exquisitely selective for protons. HCNL1 activates during hyperpolarization and conducts protons into the cytosol. Surprisingly, protons permeate through the channel’s voltage-sensing domain, whereas the pore domain is nonfunctional. Key to proton permeation is a methionine residue that interrupts the series of regularly spaced arginine residues in the S4 voltage sensor. HCNL1 forms a tetramer and thus contains four proton pores. Unlike classic HCN channels, HCNL1 is not gated by cyclic nucleotides. The channel is present in zebrafish sperm and carries a proton inward current that acidifies the cytosol. Our results suggest that protons rather than cyclic nucleotides serve as cellular messengers in zebrafish sperm. Through small modifications in two key functional domains, HCNL1 evolutionarily adapted to a low-Na+freshwater environment to conserve sperm’s ability to depolarize.

scholarly journals A sulfur-aromatic gate latch is essential for opening of the Orai1 channel pore

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Priscilla S-W Yeung ◽  
Christopher E Ing ◽  
Megumi Yamashita ◽  
Régis Pomès ◽  
Murali Prakriya
Keyword(s):  
Metal Ion ◽  
Mutational Analysis ◽  
Hydrophobic Interactions ◽  
Protein Structures ◽  
Experimental Studies ◽  
Functional Roles ◽  
Methionine Residue ◽  
Aromatic Interactions ◽  
Additional Stabilization ◽  
Dynamics Simulations

Sulfur-aromatic interactions occur in the majority of protein structures, yet little is known about their functional roles in ion channels. Here, we describe a novel molecular motif, the M101 gate latch, which is essential for gating of human Orai1 channels via its sulfur-aromatic interactions with the F99 hydrophobic gate. Molecular dynamics simulations of different Orai variants reveal that the gate latch is mostly engaged in open but not closed channels. In experimental studies, we use metal-ion bridges to show that promoting an M101-F99 bond directly activates Orai1, whereas disrupting this interaction triggers channel closure. Mutational analysis demonstrates that the methionine residue at this position has a unique combination of length, flexibility, and chemistry to act as an effective latch for the phenylalanine gate. Because sulfur-aromatic interactions provide additional stabilization compared to purely hydrophobic interactions, we infer that the six M101-F99 pairs in the hexameric channel provide a substantial energetic contribution to Orai1 activation.

The Trishomocyclopropenyl Cation. I. Direct Observation

1974 ◽  
Vol 52 (5) ◽  
pp. 855-857 ◽  
Author(s):  
S. Masamune ◽  
M. Sakai ◽  
A. V. Kemp-Jones ◽  
T. Nakashima
Keyword(s):  
Chemical Shift ◽  
Direct Observation ◽  
Time Scale ◽  
High Field ◽  
Positive Charge ◽  
Hydride Shift ◽  
First Time

The trishomocyclopropenyl cation has been prepared for the first time and is shown to be a remarkably stable, highly charge-delocalized species. The large [Formula: see text] value associated with the carbons formally carrying the positive charge, the high-field chemical shift of these carbons, and the absence of hydride shift, all are significant and are consistent with the formulation of 1 subject to the limit of the n.m.r. time scale.

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

The E-ring: interactions with plasma and implications for its evolution

1984 ◽  
Vol 75 ◽  
pp. 599-602
Author(s):  
T.V. Johnson ◽  
G.E. Morfill ◽  
E. Grun
Keyword(s):  
Time Scale ◽  
Particle Density ◽  
High Energy ◽  
Particle Removal ◽  
Density Region ◽  
Drag Forces ◽  
Orbit Evolution ◽  
History Of ◽  
Ring Particle ◽  
Ring Material

A number of lines of evidence suggest that the particles making up the E-ring are small, on the order of a few microns or less in size (Terrile and Tokunaga, 1980, BAAS; Pang et al., 1982 Saturn meeting; Tucson, AZ). This suggests that a variety of electromagnetic and plasma affects may be important in considering the history of such particles. We have shown (Morfill et al., 1982, J. Geophys. Res., in press) that plasma drags forces from the corotating plasma will rapidly evolve E-ring particle orbits to increasing distance from Saturn until a point is reached where radiation drag forces acting to decrease orbital radius balance this outward acceleration. This occurs at approximately Rhea's orbit, although the exact value is subject to many uncertainties. The time scale for plasma drag to move particles from Enceladus' orbit to the outer E-ring is ~104yr. A variety of effects also act to remove particles, primarily sputtering by both high energy charged particles (Cheng et al., 1982, J. Geophys. Res., in press) and corotating plasma (Morfill et al., 1982). The time scale for sputtering away one micron particles is also short, 102 - 10 yrs. Thus the detailed particle density profile in the E-ring is set by a competition between orbit evolution and particle removal. The high density region near Enceladus' orbit may result from the sputtering yeild of corotating ions being less than unity at this radius (e.g. Eviatar et al., 1982, Saturn meeting). In any case, an active source of E-ring material is required if the feature is not very ephemeral - Enceladus itself, with its geologically recent surface, appears still to be the best candidate for the ultimate source of E-ring material.

Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis

1987 ◽  
Vol 45 ◽  
pp. 54-55
Author(s):  
T. F. Kelly ◽  
P. J. Lee ◽  
E. E. Hellstrom ◽  
D. C. Larbalestier
Keyword(s):  
Rare Earth ◽  
High Field ◽  
Transport Current ◽  
Total Thickness ◽  
New Class ◽  
Ceramic Superconductors ◽  
Current Densities ◽  
Group Ii ◽  
Eds Microanalysis

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.

High-field magnetoluminescence of ZnSe quantum wires

1998 ◽  
Vol 184-185 (1-2) ◽  
pp. 339-342 ◽  
Author(s):  
L Parthier
Keyword(s):  
High Field ◽  
Quantum Wires
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