Thin filament activation probed by fluorescence of N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1,3-diazole-labeled troponin I incorporated into skinned fibers of rabbit psoas muscle.
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A method is described for the exchange of native troponin of single rabbit psoas muscle fibers for externally applied troponin complexes without detectable impairment of functional properties of the skinned fibers. This approach is used to exchange native troponin for rabbit skeletal troponin with a fluorescent label (N-((2-(iodoacetoxy)ethyl)-N-methyl)amino-7-nitrobenz-2-oxa-1, 3-diazole, IANBD) on Cys(133) of the troponin I subunit. IANBD-labeled troponin I has previously been used in solution studies as an indicator for the state of activation of reconstituted actin filaments (. Proc. Natl. Acad. Sci. USA. 77:7209-7213). In the skinned fibers, the fluorescence of this probe is unaffected when cross-bridges in their weak binding states attach to actin filaments but decreases either upon the addition of Ca(2+) or when cross-bridges in their strong binding states attach to actin. Maximum reduction is observed when Ca(2+) is raised to saturating concentrations. Additional attachment of cross-bridges in strong binding states gives no further reduction of fluorescence. Attachment of cross-bridges in strong binding states alone (low Ca(2+) concentration) gives only about half of the maximum reduction seen with the addition of calcium. This illustrates that fluorescence of IANBD-labeled troponin I can be used to evaluate thin filament activation, as previously introduced for solution studies. In addition, at nonsaturating Ca(2+) concentrations IANBD fluorescence can be used for straightforward classification of states of the myosin head as weak binding (nonactivating) and strong binding (activating), irrespective of ionic strength or other experimental conditions. Furthermore, the approach presented here not only can be used as a means of exchanging native skeletal troponin and its subunits for a variety of fluorescently labeled or mutant troponin subunits, but also allows the exchange of native skeletal troponin for cardiac troponin. (+info)
X-ray diffraction studies of human erythrocyte membrane structure.
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Small angle x-ray diffraction patterns have been obtained from ordered arrays of hemoglobin-free human erthyrocyte membranes by use of improved techniques. Diffraction data have been recorded to 9 A resolution on samples whose lattice periodicity was varied (by changing humidity) from 55.5 A to 69.6 A. The observed reflections permitted tracing the intensity transform of the membranes. Phases for the reflections were assigned by the minimum wavelength principle. An electron density profile was then obtained by Fourier inversion, and yielded a symmetric membrane about 55 A in width. This structure can account for the previously reported diffuse scattering observed in other preparations (thus rendering unnecessary the proposed assignment of this scattering to a separated lipoprotein phase) and for the continuous scattering that we have recorded from isolated membranes in buffer. Lower resolution data that we have obtained from ultracentrifugally prepared lattices in buffer (and therefore without dehydration) are consistent with the above results, and support our view that we are observing diffraction from intact membranes. (+info)
X-ray crystallographic visualization of drug-nucleic acid intercalative binding: structure of an ethidium-dinucleoside monophosphate crystalline complex, Ethidium: 5-iodouridylyl (3'-5') adenosine.
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We have cocrystallized the drug ethidium bromide with the dinucleoside monophosphate 5-iodouridylyl(3'-5')adenosine and have solved the three-dimensional structure to atomic resolution by x-ray crystallography. This has allowed the direct visualization of intercalative binding by this drug to a fragment of a nucleic acid double helix. (+info)
Crystallization of nerve growth factor from mouse submaxillary glands.
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Crystals of the nerve growth factor protein were grown by vapor diffusion from ethanol solution. The crystals are hexagonal, belonging to space group P622 (or its enantiomorph) with a equals 56.1 A, c equals 181.4 A, and V equals 494,400 A. The unit cell contains six molecules of dimeric protein and thus has one monomer per asymmetric unit. The diffraction pattern extends to at least 2.7 A, indicating that this crystal form is suitable for structural analysis to near-atomic resolution. (+info)
Preparation of large monodomain phospholipid bilayer smectic liquid crystals.
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A technique for the preparation of large monodomain phospholipid bilayer arrays is described. Evidence for the monodomain nature of the samples, obtained from optical birefringence, light scattering, and x-ray diffraction experiments, is presented. (+info)
A new approach to empirical intermolecular and conformational potential energy functions. II. Applications to crystal packing, rotational barriers, and conformational analysis.
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An empirical potential energy function based on the interactions of electrons and nuclei (EPEN) has been tested on molecules other than those used for its parameterization. The results indicate that this energy function is able to predict reliably the lowest energy conformations, the potential energy differences between conformations, rotational barrier heights, and dipole moments for a series of alkanes, amines, alcohols, and carbohydrates. Crystal packing studies on n-hexane, n-octane, methylamine, methanol, and alpha-d-glucose, using this same potential, indicate that it is also reliable for calculating intermolecular interaction energies and low-energy orientations. (+info)
Assessment of some problems associated with prediction of the three-dimensional structure of a protein from its amino-acid sequence.
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It is shown that most present empirical prediction algorithms provide information about the conformational states of individual residues, but give little information about the three-dimensional structure of a protein. It is necessary to predict the conformational state of every residue before the resulting structure can serve as a starting conformation to compute the native structure. It is also shown that even a perfect five-state algorithm (which does not include long-range interactions from disulifide loop closing or solvation) will not lead to a globular structure resembling the native one. However, starting from the results of a perfect prediction algorithm, it appears that conformational energy minimization (with long-range interactions included) can lead to a structure having the general features of the native protein. (+info)
Crystal structure of bovine Cu,Zn superoxide dismutase at 3 A resolution: chain tracing and metal ligands.
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An electron density map at 3 angstrom resolution has been calculated for Cu2+, Zn2+ superoxide dismutase from bovine erythrocytes, and the course of the main chain has been traced. The dominant structural feature is an 8-stranded barrel of antiparallel beta-pleated sheet. There is one very short helical section and two long loops of non-repetitive structure. The Cu and Zn are bound between the loops and one side of the beta barrel and are about 6 Angstrom apart, with a common histidine ligand. The Cu has four histidine ligands in a somewhat distorted square plane, and the Zn has three histidines and an aspartate in approximately tetrahedral arrangement. The two coppers of a dimer are about 34 Angstrom apart. The two subunits have essentially the same conformation and have an extensive contact area that mainly involves hydrophobic side chain interactions. The overall folding pattern of the polypeptide chain is very similar to that of an immunoglobulin domain. (+info)