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101.
Conserved sequence motifs in the unorthodox BvgS two-component sensor protein ofBordetella pertussis
The unorthodox two-component sensor protein BvgS ofBordetella pertussis contains several interesting sequence motifs of unknown functional relevance, such as a histidine motif in its output domain, which is conserved among several unorthodox sensor proteins, a putative nucleotide binding site [Walker box type A] in its linker region, and a region in its periplasmic domain with significant homology to the TonB protein ofEscherichia coli. We investigated potential functions of these sequences by constructingB. pertussis strains that express mutant BvgS derivatives. The His1172 residue in the output domain was exchanged for Gln, and the Walker motif was mutated either by the replacement of Lys625 by Arg, or of Gly624 by Val and Lys625 by Leu. To analyse the TonB motif, the periplasmic domain of BvgS was replaced with the corresponding domain of EvgS, anE. coli sensor that is highly homologous to BvgS but lacks the similarity with TonB. All mutations except the conservative Lys/Arg exchange in the Walker box caused the inactivation of BvgS, indicating the functional importance of the conserved motifs. The activity of the mutant proteins could be restored by complementation in trans with various separately expressed, truncated parts of BvgS. Mutations in the BvgS receiver domain could be complemented not only by a construct expressing the wild-type receiver and output domains, but also by the derivative containing the His-Gln exchange. Therefore, the histidine motif, although important for BvgS function, is not essential for complementation of BvgS mutants. The mutations in the Walker box and in the periplasmic domain could be complemented by a truncated BvgS derivative lacking the receiver and output domains. The characterization of a spontaneous revertant of the strain expressing the originally inactive EvgS/BvgS hybrid protein revealed the presence of a mutation in the BvgS linker region, conferring constitutive activity on the protein. As TonB energizes transport processes across the outer membrane ofE. coli, the strain expressing the constitutive EvgS/BvgS hybrid protein lacking the TonB motif was used in preliminary investigations of a possible direct involvement of BvgS in transport processes. 相似文献
102.
Gross MR 《Trends in ecology & evolution》1996,11(2):92-98
Not all members of a sex behave in the same way. Frequency- and statusdependent selection have given rise to many alternative reproductive phenotypes within the sexes. The evolution and proximate control of these alternatives are only beginning to be understood. Although game theory has provided a theoretical framework, the concept of the mixed strategy has not been realized in nature, and alternative strategies are very rare. Recent findings suggest that almost all alternative reproductive phenotypes within the sexes are due to alternative tactics within a conditional strategy, and, as such, while the average fitnesses of the alternative phenotypes are unequal, the strategy is favoured in evolution. Proximate mechanisms that underlie alternative phenotypes may have many similarities with those operating between the sexes. 相似文献
103.
104.
105.
Thomas Schnyder Peter Tittmann Hanspeter Winkler Heinz Gross Theo Wallimann 《Journal of structural biology》1995,114(3)
Octamers of mitochondrial creatine kinase (Mi-CK) wore modified with the thiol-specific reagents N-ethylmaleimide or the gold-coupled derivative, maleidoyl undecagold. The kinetics of inhibition of the Mi-CK catalysis was shown to be comparable for both reagents, suggesting that the large gold cluster complex is accessible to the reactive cysteines. SDS-PAGE analysis revealed that two of eight cysteines per Mi-CK monomer were labeled with maleidoyl undecagold with a similar affinity for the functional maleimide group. Gel exclusion chromatography of labeled molecules showed that the octameric structure of Mi-CK was preserved after thiol modification. Freeze-dried gold-labeled octamers visualized by electron microscopy under cryoconditions were enhanced in contrast and showed a well-preserved fourfold symmetry of the end-on view, Image analysis of gold-labeled Mi-CK exhibited an averaged end-on view with four strong contrast signals located at the periphery of the notamer, whereas the center of the molecule remained electron translucent. We conclude that the two cysteine residues per monomer labeled with maleidoyl undecagold are located at the octamer's perimeter and we discuss the possible role of these reactive cysteines in enzyme catalysis. 相似文献
106.
The exchange of the discriminator base A73 for G is alone sufficient to convert human tRNA(Leu) into a serine-acceptor in vitro. 总被引:6,自引:1,他引:5
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Transfer RNA (tRNA) identify is maintained by the highly specific interaction of a few defined nucleotides or groups of nucleotides, called identity elements, with the cognate aminoacyl-tRNA synthetase, and by nonproductive interactions with the other 19 aminoacyl-tRNA synthetases. Most tRNAs have a set of identity elements in at least two locations, commonly in the anticodon loop or in the acceptor stem, and at the discriminator base position 73. We have used T7 RNA polymerase transcribed tRNAs to demonstrate that the sole replacement of the discriminator base A73 of human tRNA(Leu) with the tRNA(Ser)-specific G generates a complete identity switch to serine acceptance. The reverse experiment, the exchange of G73 in human tRNA(Ser) for the tRNA(Leu-specific A, causes a total loss of serine specificity without creating any leucine acceptance. These results suggest that the discriminator base A73 of human tRNA(Leu) alone protects this tRNA against serylation by seryl-tRNA synthetase. This is the first report of a complete identity switch caused by an exchange of the discriminator base alone. 相似文献
107.
Mühlebach S. M. Gross M. Wirz T. Wallimann T. Perriard J. -C. Wyss M. 《Molecular and cellular biochemistry》1994,133(1):245-262
Comparisons of the protein sequences and gene structures of the known creatine kinase isoenzymes and other guanidino kinases revealed high homology and were used to determine the evolutionary relationships of the various guamidino kinases. A CK framework is defined, consisting of the most conserved sequence blocks, and diagnostic boxes are identified which are characteristic for anyone creatine kinase isoenzyme (e.g. for vertebrate B-CK) and which may serve to distinguish this isoenzyme from all others (e.g. from M-CKs and Mi-CKs). Comparison of the guanidino kinases by near-UV and far-UV circular dichroism further indicates pronounced conservation of secondary structure as well as of aromatic amino acids that are involved in catalysis.Abbreviations GuaK
guanidino kinase
- CK
creatine kinase
- B-and M-CK
brain and muscle cytosolic CK isoenzyme
- Mi-CK
mitochondrial CK isoenzyme
- ArgK
arginine kinase
- Cr
creatine
- PCr
phosphorylcreatine
- PArg
phosphorylarginine 相似文献
108.
109.
Calcium uptake by microsomal membranes from the cellular slime mould Dictyostelium discoideum was measured using Calcium Green-2 as a fluorescent probe of external free Ca2+ concentration. High-affinity Ca2+ uptake was found to be completely inhibited by low concentrations of vanadate, but not by thapsigargin, suggesting that the activity is mediated by a Ca2+-ATPase distinct from sarco(endo)plasmic reticulum type of higher animal cells. On sucrose density gradients, Ca2+ uptake distributes with vacuolar proton pump activity and part of the observed Ca2+ uptake is dependent on the pH gradient generated by the vacuolar-type H+-ATPase, indicating that the Ca2+ pump is located on both acidic and non-acidic vesicles, possibly derived from the H+-ATPase-rich contractile vacuole complex. 相似文献
110.
Elham A. Ghabbour Ahmed H. Khairy Donald P. Cheney Verena Gross Geoffrey Davies Thomas R. Gilbert Xinyu Zhang 《Journal of applied phycology》1994,6(5-6):459-468
A standard humic acid extraction procedure has been used to isolate dark brown organic residues from samples of the macroscopic marine brown algaPilayella littoralis. The residues are insoluble in water, but soluble at high pH, and are similar in elemental composition, ash content, UV-visible, IR, PMR and X-Ray fluorescence spectra, X-Ray diffractograms and scanning electron micrographs to residues of a humic acid isolated from municipal compost. These results indicate thatPilayella produces humic acids.Author for correspondence 相似文献