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SYNTHETIC DEOXYRIBOPOLYNUCLEOTIDES AS TEMPLATES FOR RIBONUCLEIC ACID POLYMERASE: THE FORMATION AND CHARACTERIZATION OF A RIBOPOLYNUCLEOTIDE WITH A REPEATING TRINUCLEOTIDE SEQUENCE 总被引:5,自引:3,他引:5
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Consequences of amino acid insertions and/or deletions in transmembrane helix C of bacteriorhodopsin.
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T Marti H Otto S J R?sselet M P Heyn H G Khorana 《Proceedings of the National Academy of Sciences of the United States of America》1992,89(4):1219-1223
Six bacterioopsin mutants containing either single amino acid deletions (delta A84, delta L87), insertions (delta 85A, delta 88A), or both deletions and insertions (delta A84/delta 88A, delta 85A/delta L87) within the first two turns of transmembrane helix C, starting from the extracellular side, have been prepared. The mutant apoproteins refold in phospholipid/detergent micelles and display secondary structures similar to that of the wild type. However, the mutants delta 88A and delta A84/delta 88A do not form a chromophore with retinal. The regenerated chromophore of delta 85A displays absorption maxima and retinal isomer compositions in the dark- and light-adapted states similar to those of the wild type. In delta A84, delta L87, and delta 85A/delta L87 these chromophore properties are altered, and the structures are less stable than that of the wild type, as shown by an enhanced rate of reaction with hydroxylamine in the dark, an increased pKa of the denaturation at acidic pH, and a decreased pKa of Schiff base deprotonation. Proton translocation is abolished in the delta A84 and delta 85A/delta L87 mutants, whereas in delta 85A and delta L87 the activity is reduced to about 25% of the wild-type value at pH 6. The overall properties of the delta 85A, delta 85A/delta L87, and delta L87 mutants indicate that the deletions and/or insertions result in displacement of residues Arg-82, Asp-85, or Asp-96, respectively, which participate in proton translocation. The results are compatible with a helical structure for transmembrane segment C and emphasize the flexibility of intramolecular contacts in bacteriorhodopsin. 相似文献
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Effect of genetic modification of tyrosine-185 on the proton pump and the blue-to-purple transition in bacteriorhodopsin. 总被引:1,自引:0,他引:1
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D J Jang M A el-Sayed L J Stern T Mogi H G Khorana 《Proceedings of the National Academy of Sciences of the United States of America》1990,87(11):4103-4107
The retinylidene chromophore mutant (Y185F) of bacteriorhodopsin, in which Tyr-185 is substituted by phenylalanine, is examined and compared with wild-type bacteriorhodopsin expressed in Escherichia coli; both were reinstituted similarly in vesicles. The Y185F mutant shows (at least) two distinct spectra at neutral pH. Upon light absorption, the blue species (which absorbs in the red) behaves as if "dead"--i.e., neither its tyrosine nor its protonated Schiff base undergoes deprotonation nor does its tryptophan fluorescence undergo quenching. This result is unlike either the purple species (which absorbs in the blue) or wild-type bacteriorhodopsin expressed in E. coli. As the pH increases, both the color changes and the protonated Schiff base deprotonation efficiency suggest a blue-to-purple transition of the Y185F mutant near pH 9. If this blue-to-purple transition of Y185F corresponds to the blue-to-purple transition of purple-membrane (native) bacteriorhodopsin (occurring at pH 2.6) and of wild-type bacteriorhodopsin expressed in E. coli (occurring at pH 5), the protein-conformation changes of this transition as well as the protonated Schiff base deprotonation may be controlled not by surface pH alone, but rather by the coupling between surface potential and the general protein internal structure around the active site. The results also suggest that Tyr-185 does not deprotonate during the photocycle in purple-membrane bacteriorhodopsin. 相似文献
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Marc Carrier Alok A. Khorana Patricia Moretto Grégoire Le Gal Rebecca Karp Jeffrey I. Zwicker 《The American journal of medicine》2014