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61.
Xabier Agirrezabala Ekaterina Samatova Meline Macher Marija Liutkute Manisankar Maiti David GilCarton Jiri Novacek Mikel Valle Marina V Rodnina 《The EMBO journal》2022,41(4)
Cellular proteins begin to fold as they emerge from the ribosome. The folding landscape of nascent chains is not only shaped by their amino acid sequence but also by the interactions with the ribosome. Here, we combine biophysical methods with cryo‐EM structure determination to show that folding of a β‐barrel protein begins with formation of a dynamic α‐helix inside the ribosome. As the growing peptide reaches the end of the tunnel, the N‐terminal part of the nascent chain refolds to a β‐hairpin structure that remains dynamic until its release from the ribosome. Contacts with the ribosome and structure of the peptidyl transferase center depend on nascent chain conformation. These results indicate that proteins may start out as α‐helices inside the tunnel and switch into their native folds only as they emerge from the ribosome. Moreover, the correlation of nascent chain conformations with reorientation of key residues of the ribosomal peptidyl‐transferase center suggest that protein folding could modulate ribosome activity. 相似文献
62.
Regulation of animal oocyte maturation is hypothesized to involve heterotrimeric G-proteins. It is difficult to test this hypothesis though without knowing what G-proteins are present in these cells and where are they localized. We set out to test the hypothesis that G-proteins regulate maturation in the sea urchin oocyte by identifying resident G-proteins in oocytes and eggs, and then investigating their function. We find four families of G-protein alpha-subunits (Galphai, Galphaq, Galphas, and Galpha12) present in both oocytes and eggs of the sea urchin. Three of them, Galphai, Galphaq, and Galphas are present on the plasma membrane of the oocyte, while the fourth is located on cytoplasmic vesicles. Upon oocyte maturation, these proteins remain in eggs, and continue to be expressed in embryonic tissues. To test the functional contribution of the G-proteins to the regulation of oocyte maturation, we employ specific intervening reagents, including antibodies and competitor peptides to each Galpha subunit, and specific Galpha toxins. We find that Gi is a main candidate for a positive regulator of sea urchin oocyte maturation. These studies provide a foundation to further test specific hypotheses of the G-protein mediated regulation of oocyte maturation, fertilization, and early development in the sea urchin. 相似文献
63.
Correia H Medina R Hernández A Bustamante E Chakraburtty K Herrera F 《Memórias do Instituto Oswaldo Cruz》2004,99(7):733-737
A ribosome association factor (AF) was isolated from the yeast Sacchharomyces cerevisiae. Partial amino acid sequence of AF was determined from its fragment of 25 kDa isolated by treating AF with 2-(2-nitrophenylsulfenyl)-3-methyl-3'-Bromoindolenine (BNPS-skatole). This sequence has a 86% identity to the product of the single-copy S. cerevisiae STM1 gene that is apparently involved in several events like binding to quadruplex and triplex nucleic acids and participating in apoptosis, stability of telomere structures, cell cycle, and ribosomal function. Here we show that AF and Stm1p share some characteristics: both bind to quadruplex and Pu triplex DNA, associates ribosomal subunits, and are thermostable. These observations suggest that these polypeptides belong to a family of proteins that may have roles in the translation process. 相似文献
64.
Passive antibody therapy for infectious diseases 总被引:5,自引:0,他引:5
Antibody-based therapies are currently undergoing a renaissance. After being developed and then largely abandoned in the twentieth century, many antibody preparations are now in clinical use. However, most of the reagents that are available target non-infectious diseases. Interest in using antibodies to treat infectious diseases is now being fuelled by the wide dissemination of drug-resistant microorganisms, the emergence of new microorganisms, the relative inefficacy of antimicrobial drugs in immunocompromised hosts and the fact that antibody-based therapies are the only means to provide immediate immunity against biological weapons. Given the need for new antimicrobial therapies and many recent technological advances in the field of immunoglobulin research, there is considerable optimism regarding renewed applications of antibody-based therapy for the prevention and treatment of infectious diseases. 相似文献
65.
To elucidate the general constraints imposed on the structure of the D- and T-loops in functional tRNAs, active suppressor tRNAs were selected in vivo from a combinatorial tRNA gene library in which several nucleotide positions of these loops were randomized. Analysis of the nucleotide sequences of the selected clones demonstrates that among the randomized nucleotides, the most conservative are nucleotides 54 and 58 in the T-loop. In most cases, they make the combination U54-A58, which allows the formation of the normal reverse Hoogsteen base pair. Surprisingly, other clones have either the combination G54-A58 or G54-G58. However, molecular modeling shows that these purine–purine base pairs can very closely mimic the reverse Hoogsteen base pair U-A and thus can replace it in the T-loop of a functional tRNA. This places the reverse Hoogsteen base pair 54-58 as one of the most important structural aspects of tRNA functionality. We suggest that the major role of this base pair is to preserve the conformation of dinucleotide 59–60 and, through this, to maintain the general architecture of the tRNA L-form. 相似文献
66.
Cleavage of DNA without loss of genetic information by incorporation of a disaccharide nucleoside 下载免费PDF全文
Nauwelaerts K Vastmans K Froeyen M Kempeneers V Rozenski J Rosemeyer H Van Aerschot A Busson R Lacey JC Efimtseva E Mikhailov S Lescrinier E Herdewijn P 《Nucleic acids research》2003,31(23):6758-6769
A ribose residue inserted between the 3′-OH of one nucleotide and the 5′-phosphate group of the next nucleotide, functions as a site-specific cleavage site within DNA. This extra ribose does not interrupt helix formation and it protects duplex DNA against cleavage by restriction enzymes. Cleavage can be obtained with periodate and all ribose fragments can be removed with sodium hydroxide. As a result of this, an intact natural oligodeoxynucleotide is obtained after ligation reaction, which means that site-specific cleavage and recovering of intact DNA occurs without loss of genetic information. 相似文献
67.
Oligomerization of soluble Fas antigen induces its cytotoxicity 总被引:6,自引:0,他引:6
Proussakova OV Rabaya NA Moshnikova AB Telegina ES Turanov A Nanazashvili MG Beletsky IP 《The Journal of biological chemistry》2003,278(38):36236-36241
Soluble Fas antigen can protect cells against Fas-mediated apoptosis. High level soluble Fas antigen characteristic for blood of patients with autoimmune disease or cancer is believed to prevent the elimination of autoimmune lymphocytes or tumor cells. Here we first report that human recombinant FasDeltaTM, i.e. soluble Fas generated by alternative splicing of the intact exon 6, is capable of inducing death of transformed cells by "reverse" apoptotic signaling via transmembrane Fas ligand. FasDeltaTM, as well as transmembrane Fas antigen, can be either monomeric or oligomeric, and both its forms are efficient in blocking Fas-mediated apoptosis, although the cytotoxic activity is exhibited solely by the latter. An in vivo analysis of soluble Fas antigen showed that unlike in healthy controls, nearly the total FasDeltaTM present in sera of rheumatoid arthritis patients was oligomeric. This resulted in suppression of cell proliferation in the experimental sera and in its promotion in controls. Thus, oligomerization/depolymerization of soluble Fas antigen can regulate its activity and contribute to the pathogenesis of autoimmune diseases and cancer. 相似文献
68.
It is often assumed mutant frequencies, as measured in a DNA sample, faithfully represent basic mutation rates associated with these mutations. This paradigm was extremely helpful for in vitro studies of the mechanisms of mutagenesis/repair and causes of mutations. However, in vivo, mutant fractions appear to vary dramatically and randomly from sample to sample. It's unlikely that basic mutational rates vary so much. Such variations are probably caused by clonal expansions of mutants within tissue. Whether a particular tissue sample includes an expansion or not, is a matter of chance, which explains the observed random fluctuations of mutant fractions. Well-known examples of clonal expansions involve pathological conditions such as cancer or mitochondrial disease. It is less appreciated that even in normal tissue, expansions of somatic mutants create local deviations from the "expected" mutant frequencies. The sizes of clonal expansions appear to span a wide range and thus, may affect samples of various sizes, from individual cells to individuals. In conclusion, human body appears to be a sort of a "gambling ground" for clonally expanding mutants. We speculate that expansion of early mutants rather than de novo mutation at old age may be the major source of at least some aging-specific mutants in our bodies. 相似文献
69.
Fenech M Bonassi S Turner J Lando C Ceppi M Chang WP Holland N Kirsch-Volders M Zeiger E Bigatti MP Bolognesi C Cao J De Luca G Di Giorgio M Ferguson LR Fucic A Lima OG Hadjidekova VV Hrelia P Jaworska A Joksic G Krishnaja AP Lee TK Martelli A McKay MJ Migliore L Mirkova E Müller WU Odagiri Y Orsiere T Scarfì MR Silva MJ Sofuni T Surralles J Trenta G Vorobtsova I Vral A Zijno A Suralles J;HUman MicroNucleus project 《Mutation research》2003,534(1-2):45-64
One of the objectives of the HUman MicroNucleus (HUMN) project is to identify the methodological variables that have an important impact on micronucleus (MN) or micronucleated (MNed) cell frequencies measured in human lymphocytes using the cytokinesis-block micronucleus assay. In a previous study we had shown that the scoring criteria used were likely to be an important variable. To determine the extent of residual variation when laboratories scored cells from the same cultures using the same set of standard scoring criteria, an inter-laboratory slide-scoring exercise was performed among 34 laboratories from 21 countries with a total of 51 slide scorers involved. The results of this study show that even under these optimized conditions there is a great variation in the MN frequency or MNed cell frequency obtained by individual laboratories and scorers. All laboratories ranked correctly the MNed cell frequency in cells from cultures that were unirradiated, or exposed to 1 or 2Gy of gamma rays. The study also estimated that the intra-scorer median coefficient of variation for duplicate MNed cell frequency scores is 29% for unexposed cultures and 14 and 11% for cells exposed to 1 and 2Gy, respectively. These values can be used as a standard for quality or acceptability of data in future studies. Using a Poisson regression model it was estimated that radiation dose explained 67% of the variance, while staining method, cell sample, laboratory, and covariance explained 0.6, 0.3, 6.5, and 25.6% of the variance, respectively, leaving only 3.1% of the variance unexplained. As part of this exercise, nucleoplasmic bridges were also estimated by the laboratories; however, inexperience in the use of this biomarker of chromosome rearrangement was reflected in the much greater heterogeneity in the data and the unexplained variation estimated by the Poisson model. The results of these studies indicate clearly that even after standardizing culture and scoring conditions it will be necessary to calibrate scorers and laboratories if MN, MNed cell and nucleoplasmic bridge frequencies are to be reliably compared among laboratories and among populations. 相似文献
70.
Havener JM Nick McElhinny SA Bassett E Gauger M Ramsden DA Chaney SG 《Biochemistry》2003,42(6):1777-1788
DNA polymerase mu (pol mu) is a member of the pol X family of DNA polymerases, and it shares a number of characteristics of both DNA polymerase beta (pol beta) and terminal deoxynucleotidyl transferase (TdT). Because pol beta has been shown to perform translesion DNA synthesis past cisplatin (CP)- and oxaliplatin (OX)-GG adducts, we determined the ability of pol mu to bypass these lesions. Pol mu bypassed CP and OX adducts with an efficiency of 14-35% compared to chain elongation on undamaged DNA, which is second only to pol eta in terms of bypass efficiency. The relative ability of pol mu to bypass CP and OX adducts was dependent on both template structure and sequence context. Since pol mu has been shown to be more efficient on gapped DNA templates than on primed single-stranded DNA templates, we determined the ability of pol mu to bypass Pt-DNA adducts on both primed single-stranded and gapped templates. The bypass of Pt-DNA adducts by pol mu was highly error-prone on all templates, resulting in 2, 3, and 4 nt deletions. We postulate that bypass of Pt-DNA adducts by pol mu may involve looping out the Pt-GG adduct to allow chain elongation downstream of the adduct. This reaction appears to be facilitated by the presence of a downstream "acceptor" and a gap large enough to provide undamaged template DNA for elongation past the adduct, although gapped DNA is clearly not required for bypass. 相似文献