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排序方式: 共有73条查询结果,搜索用时 15 毫秒
1.
I N Trakht I D Grozdova N N Guliaev E S Severin N V Gnuchev 《Biokhimii?a (Moscow, Russia)》1980,45(5):788-792
The true slime mould Physarum polycephalum was treated with various agents by spraying them upon the cell surface 4 hrs before the second synchronous mitosis. The onset of mitosis was considerably approximated after the plasmodium treatment with protein kinases from rat hepatoma or Ph. polycephalum at the late G2 phase. The catalytic and regulatory subunits of cAMP-dependent pig brain protein kinase caused retardation of mitosis, while the holoenzyme, casein kinase and alkaline phosphatase did not affect the timing of mitosis. The cyclic nucleotides and inhibitors of their metabolic enzymes were used to investigate the role of phosphorylation processes in the mitotic cycle. 相似文献
2.
Positive selection is a general phenomenon in the evolution of abalone sperm lysin 总被引:36,自引:21,他引:15
Lysin is a 16kDa acrosomal protein used by abalone sperm to create a hole
in the egg vitelline envelope (VE). The interaction of lysin with the VE is
species-selective and is one step in the multistep fertilization process
that restricts heterospecific (cross-species) fertilization. For this
reason, the evolution of lysin could play a role in establishing prezygotic
reproductive isolation between species. Previously, we sequenced sperm
lysin cDNAs from seven California abalone species and showed that positive
Darwinian selection promotes their divergence. In this paper an additional
13 lysin sequences are presented representing species from Japan, Taiwan,
Australia, New Zealand, South Africa, and Europe. The total of 20 sequences
represents the most extensive analysis of a fertilization protein to date.
The phylogenetic analysis divides the sequences into two major clades, one
composed of species from the northern Pacific (California and Japan) and
the other composed of species from other parts of the world. Analysis of
nucleotide substitution demonstrates that positive selection is a general
process in the evolution of this fertilization protein. Analysis of
nucleotide and codon usage bias shows that neither parameter can account
for the robust data supporting positive selection. The selection pressure
responsible for the positive selection on lysin remains unknown.
相似文献
3.
R Krauspe G K Kovaleva N N Guliaev L A Baranova M B Agalarova 《Biokhimii?a (Moscow, Russia)》1978,43(4):656-661
The interaction between modifying ATP analogs containing alkylating or phosphorylating groups in the polyphosphate moiety of the ATP molecule and leucyl-tRNA synthetases from cytoplasm and chloroplasts of Euglena gracilis (strain Z) was studied. It was shown that most of the ATP analogs irreversibly inhibit the cytoplasmic enzyme, having no inhibiting effect on the chloroplast synthetase. The kinetic constants K1 and k2 for the interaction between the most effective irreversible inhibitors and the cytoplasmic enzyme were determined. The data on the protection of the enzyme activity by substrates against irreversible inhibition suggest, that the effect of the adenosine 5'-(beta-chloroethyl phosphate) is directed to the ATP-binding site of the cytoplasmic enzyme, whereas the mixed anhydride of AMP and mesithylene carbonic acid acts predominantly on the binding site of 3'-terminal adenosine of the tRNALeu molecule. ATP analogs may be effectively used for affinity labelling of the cytoplasmic leucyl-tRNA synthetase. 相似文献
4.
5.
The environmental carcinogen glycidaldehyde (GDA) and therapeutic chloroethylnitrosoureas (CNUs) can form hydroxymethyl etheno and ring-saturated ethano bases, respectively. The mutagenic potential of these adducts relies on their miscoding properties and repair efficiency. In this work, the ability of human thymine-DNA glycosylase (TDG) to excise 8-(hydroxymethyl)-3,N(4)-ethenocytosine (8-hm-varepsilonC) and 3,N(4)-ethanocytosine (EC) was investigated and compared with varepsilonC, a known substrate for TDG. When tested using defined oligonucleotides containing a single adduct, TDG is able to excise 8-hm-varepsilonC but not EC. The 8-hm-varepsilonC activity mainly depends on guanine pairing with the adduct. TDG removes 8-hm-varepsilonC less efficiently than varepsilonC but its activity can be significantly enhanced by human AP endonuclease 1 (APE1), a downstream enzyme in the base excision repair. TDG did not show any detectable activity toward EC when placed in various neighboring sequences, including the 5'-CpG site. Molecular modeling revealed a possible steric clash between the non-planar EC exocyclic ring and residue Asn 191 within the TDG active site, which could account for the lack of TDG activity toward EC. TDG was not active against the bulkier exocyclic adduct 3,N(4)-benzethenocytosine, nor the two adenine derivatives with same modifications as the cytosine derivatives, 7-hm-varepsilonA and EA. These findings expand the TDG substrate range and aid in understanding the structural requirements for TDG substrate specificity. 相似文献
6.
Bacteria adapting to living in a host cell caused the most salient events in the evolution of eukaryotes, namely the seminal fusion with an archaeon, and the emergence of both mitochondrion and chloroplast. A bacterial clade that may hold the key to understanding these events is the deep-branching gammaproteobacterial order Legionellales—containing among others Coxiella and Legionella—of which all known members grow inside eukaryotic cells. Here, by analyzing 35 novel Legionellales genomes mainly acquired through metagenomics, we show that this group is much more diverse than previously thought, and that key host-adaptation events took place very early in its evolution. Crucial virulence factors like the Type IVB secretion (Dot/Icm) system and two shared effector proteins were gained in the last Legionellales common ancestor (LLCA). Many metabolic gene families were lost in LLCA and its immediate descendants, including functions directly and indirectly related to molybdenum metabolism. On the other hand, genome sizes increased in the ancestors of the Legionella genus. We estimate that LLCA lived approximately 1.89 Ga, probably predating the last eukaryotic common ancestor by approximately 0.4–1.0 Gy. These elements strongly indicate that host adaptation arose only once in Legionellales, and that these bacteria were using advanced molecular machinery to exploit and manipulate host cells early in eukaryogenesis. 相似文献
7.
Structural insights by molecular dynamics simulations into differential repair efficiency for ethano-A versus etheno-A adducts by the human alkylpurine-DNA N-glycosylase 总被引:1,自引:1,他引:0
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1,N6-ethenoadenine adducts (εA) are formed by known environmental carcinogens and found to be removed by human alkylpurine-DNA N-glycosylase (APNG). 1,N6-ethanoadenine (ΕA) adducts differ from εA by change of a double bond to a single bond in the 5-member exocyclic ring and are formed by chloroethyl nitrosoureas, which are used in cancer therapy. In this work, using purified recombinant human APNG, we show that ΕA is a substrate for the enzyme. However, the excision efficiency of ΕA was 65-fold lower than that of εA. Molecular dynamics simulation produced similar structural motifs for εA and ΕA when incorporated into a DNA duplex, suggesting that there are no specific conformational features in the DNA duplex which can account for the differences in repair efficiency. However, when ΕA was modeled into the APNG active site, based on the APNG/εA-DNA crystallographic coordinates, in structures produced by 2 ns molecular dynamics simulation, we observed weakening in the stacking interaction between ΕA and aromatic side chains of the key amino acids in the active site. In contrast, the planar εA is better stacked at the enzyme active site. We propose that the observed destabilization of the ΕA adduct at the active site, such as reduced stacking interactions, could account for the biochemically observed weaker recognition of ΕA by APNG as compared to εA. 相似文献
8.
8-(Hydroxymethyl)-3,N(4)-etheno-C (8-HM-epsilonC) is an exocyclic adduct resulting from the reaction of dC with glycidaldehyde, a mutagen and animal carcinogen. This compound has now been synthesized and its phosphoramidite incorporated site-specifically into a defined 25-mer oligonucleotide. In this study, the mutagenic potential of this adduct in the 25-mer oligonucleotide was investigated in an in vitro primer-template extension assay using four mammalian DNA polymerases. The miscoding potentials were also compared to those of an analogous derivative, 3,N(4)-etheno C (epsilonC), in the same sequence. Both adducts primarily blocked replication by calf thymus DNA polymerase alpha at the modified base, while human polymerase beta catalyzed measurable replication synthesis through both adducts. Nucleotide insertion experiments showed that dA and dC were incorporated by pol beta opposite either adduct, which would result in a C --> T transition or C --> G transversion. Human polymerase eta, a product of the xeroderma pigmentosum variant (XP-V) gene, catalyzed the most efficient bypass of the two lesions with 25% and 32% for 8-HM-epsilonC and epsilonC bypassed after 15 min. Varying amounts of all four bases opposite the modified bases resulted with pol eta. Human polymerase kappa primarily blocked synthesis at the base prior to the adduct. However, some specific misincorporation of dT resulted, forming an epsilonC.T or 8-HM-epsilonC.T pair. From these data, we conclude that the newly synthesized glycidaldehyde-derived adduct, 8-HM-epsilonC, is a miscoding lesion. The bypass efficiency and insertion specificity of 8-HM-epsilonC and epsilonC were similar for all four polymerases tested, which could be attributed to the similar planarity and sugar conformations for these two derivatives as demonstrated by molecular modeling studies. 相似文献
9.
A new cestode genus and species Relictolepis feodorovi gen. et sp. n. having armed scolex is described ex Clethrionomis rufocanus Sundevall, 1846 (Rodentia, Microtinae) from the Russian Far East. 相似文献
10.
Anna R Batt Commodore P St Germain Trevor Gokey Anton B Guliaev Teaster Baird Jr 《Protein science : a publication of the Protein Society》2015,24(9):1463-1474
The development of effective protease therapeutics requires that the proteases be more resistant to naturally occurring inhibitors while maintaining catalytic activity. A key step in developing inhibitor resistance is the identification of key residues in protease-inhibitor interaction. Given that majority of the protease therapeutics currently in use are trypsin-fold, trypsin itself serves as an ideal model for studying protease-inhibitor interaction. To test the importance of several trypsin-inhibitor interactions on the prime-side binding interface, we created four trypsin single variants Y39A, Y39F, K60A, and K60V and report biochemical sensitivity against bovine pancreatic trypsin inhibitor (BPTI) and M84R ecotin. All variants retained catalytic activity against small, commercially available peptide substrates [kcat/KM = (1.2 ± 0.3) × 107 M−1 s−1. Compared with wild-type, the K60A and K60V variants showed increased sensitivity to BPTI but less sensitivity to ecotin. The Y39A variant was less sensitive to BPTI and ecotin while the Y39F variant was more sensitive to both. The relative binding free energies between BPTI complexes with WT, Y39F, and Y39A were calculated based on 3.5 µs combined explicit solvent molecular dynamics simulations. The BPTI:Y39F complex resulted in the lowest binding energy, while BPTI:Y39A resulted in the highest. Simulations of Y39F revealed increased conformational rearrangement of F39, which allowed formation of a new hydrogen bond between BPTI R17 and H40 of the variant. All together, these data suggest that positions 39 and 60 are key for inhibitor binding to trypsin, and likely more trypsin-fold proteases. 相似文献