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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 18 (1994), S. 186-197 
    ISSN: 0887-3585
    Keywords: carboxypeptidas ; molecular dynamics ; enzymatic mechanisms ; peptidase mechanism ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: An MD simulation of the system carboxypeptidase A (CPA) with the tetrapeptide Val-Leu-Phe-Phe has been performed in order to learn about the substrate disposition just prior to nucleophilic attack. We have explored the model in which the substrate does not substitute the zinc-coordinated water (the “water” mechanism). The simulations do suggest as feasible that the Zn-OH2 group performs a nucleophilic attack on the Phe-Phe peptidic bond. We have also investigated the model in which the carbonyl oxygen displaces the zinc-coordinated water. In this case the substrate and Glu-270 orient themselves to allow an anhydride intermediate during the peptidic bond cleavage (the “anhydride” mechanism). Based on the results of the simulations, both “water” and “anhydride” mechanisms are structurally feasible, although the former model seems more probable on chemical grounds. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0887-3585
    Keywords: NMR ; iron-sulfur proteins ; nuclear Overhauser effect ; paramagnetic relaxation ; relaxation matrix analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: We have accounted for the effect of paramagnetism on the intensities of NOEs in a 73-residue paramagnetic metalloprotein, the reduced high-potential iron sulfur protein ISO I from Ectothiorhodospira halophila, whose solution structure had been recently solved by us. The paramagnetic effects were dealt with through a suitably modified complete relaxation matrix approach. We have then recalculated the structure through a distance geometry program by minimizing the difference between the sixth roots of the calculated and experimental NOEs.The average RMSD, calculated on residues 4-71, within the structures constituting the two families decreased from 0.67 to 0.46 Å for backbone atoms and from 1.23 to 1.06 Å for all heavy atoms. The structures in the new family are for the most part within the indetermination of the previous, less resolved, family. A few specific differences are detected and related to the presence of non-negligible paramagnetic effects, which are now properly evaluated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0887-3585
    Keywords: pseudocontact shifts ; structure calculations ; restrained energy minimization ; molecular dynamics ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The pseudocontact shifts of NMR signals, which arise from the magnetic susceptibility anisotropy of paramagnetic molecules, have been used as structural constraints under the form of a pseudopotential in the SANDER module of the AMBER 4.1 molecular dynamics software package. With this procedure, restrained energy minimization (REM) and restrained molecular dynamics (RMD) calculations can be performed on structural models by using pseudocontact shifts. The structure of the cyanide adduct of the Met80Ala mutant of the yeast iso-1-cytochrome c has been used for successfully testing the calculations. For this protein, a family of structures is available, which was obtained by using NOE and pseudocontact shifts as constraints in a distance geometry program. The structures obtained by REM and RMD calculations with the inclusion of pseudocontact shifts are analyzed. Proteins 29:68-76, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 29 (1997), S. 348-358 
    ISSN: 0887-3585
    Keywords: ferredoxin ; NMR ; paramagnetic ; relaxation ; solution structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The possibility of using the relaxation properties of nuclei for solution structure determination of paramagnetic metalloproteins is critically evaluated. First of all, it is theoretically and experimentally demonstrated that magnetization recovery in non-selective inversion recovery experiments can be approximated to an exponential in both diamagnetic and paramagnetic systems. This permits the estimate of the contribution of paramagnetic relaxation when dominant or sizable. Then, it is shown that the averaging of paramagnetic relaxation rates due to cross relaxation is often tolerably small with respect to the use of paramagnetic relaxation rates as constraints for structural determination. Finally, a protocol is proposed to use such paramagnetic relaxation rates, which depend on the sixth power of the metal to resonating nucleus distance, as constraints for solution structure determination of proteins. As an example, the available solution structure of the oxidized ferredoxin from Clostridium pasteurianum has been significantly improved in resolution especially in the proximity of the metal ions by using 69 new constraints based on paramagnetic relaxation. Proteins 29:348-358, 1997. © 1997 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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