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Biomedical subjects

N Bilgin

Publications and source records attributed to N Bilgin.

At least 127 records · Page 7Linked to original sources
PubMed1995

Phosphorylation of elongation factor Tu prevents ternary complex formation.

The elongation factor Tu (EF-Tu) is a member of the GTP/GDP-binding proteins and interacts with various partners during the elongation cycle of protein biosynthesis thereby mediating the correct binding of amino-acylated transfer RNA (aa-tRNA) to the acceptor site (A-site) of the ribosome. After GTP hydrolysis EF-Tu is released in its GDP-bound state. In vivo, EF-Tu is post-translationally modified by phosphorylation. Here we report that the phosphorylation of EF-Tu by a ribosome associated kinase activity is drastically enhanced by EF-Ts. The antibiotic kirromycin, known to block EF-Tu function, inhibits the modification. This effect is specific, since kirromycin-resistant mutants do become phosphorylated in the presence of the antibiotic. On the other hand, phosphorylated wild-type EF-Tu does not bind kirromycin. Most interestingly, the phosphorylation of EF-Tu abolishes its ability to bind aa-tRNA. In the GTP conformation the site of modification is located at the interface between domains 1 and 3 and is involved in a strong interdomain hydrogen bond. Introduction of a charged phosphate group at this position will change the interaction between the domains, leading to an opening of the molecule reminiscent of the GDP conformation. A model for the function of EF-Tu phosphorylation in protein biosynthesis is presented.

Anti-Bacterial Agents↗
PubMed1995

Stoichiometry for the elongation factor Tu.aminoacyl-tRNA complex switches with temperature.

In bacterial protein synthesis binding of an aminoacyl-transferRNA (aa-tRNA) to the ribosomal acceptor site (A-site) is catalyzed by elongation factor Tu (EF-Tu). Two guanosine triphosphates (GTPs) are hydrolyzed on EF-Tu for every bound aa-tRNA. This was rationalized by the notion of an extended ternary complex, consisting of two EF-Tu.GTPs bound to a single aa-tRNA. In this work, we combine fast kinetics with RNase A protection experiments to measure the stoichiometry between EF-Tu.GTP and aa-tRNA at 37 degrees C, where the binding is weak. We find a 2:1 stoichiometry between EF-Tu.GTP and aa-tRNA at 37 degrees C, but at 0 degree C, under otherwise similar conditions, the stoichiometry of the complex is close to 1:1. These results suggest alternative pathways for aa-tRNA binding to ribosomes, since two GTPs are hydrolyzed per peptide bond at both temperatures. At 37 degrees C, aa-tRNA enters the A-site in a pentameric complex with two EF-Tu's on which two GTPs are hydrolyzed in synchrony, when cognate codon-anticodon contact is established. This pentameric model also explains how two GTPs can be hydrolyzed on EF-Tu, without rejection of 50% of the cognate aa-tRNAs in proofreading. At 0 degree C, in contrast, two ordinary ternary complexes may form a pentameric complex on, rather than off, the ribosome. When the two EF-Tu bound GTPs are hydrolyzed, one aa-tRNA enters the A-site, and the other dissociates to the free state.

Escherichia coli↗
PubMed1995

Two GTPs are consumed on EF-Tu per peptide bond in poly(Phe) synthesis, in spite of switching stoichiometry of the EF-Tu.aminoacyl-tRNA complex with temperature.

Recent observations indicate that the stoichiometry for the complex between EF-Tu.GTP and aminoacyl-tRNA (aa-tRNA) changes with temperature. At 37 degrees C two EF-Tu.GTPs bind one aa-tRNA in an extended ternary complex, but at 0 degrees C the complex has 1:1 stoichiometry. However, the present experiments show that there are two GTPs hydrolyzed on EF-Tu per peptide bond in poly(Phe) synthesis at 37 degrees C as well as at 0 degrees C. This indicates two different pathways for the enzymatic binding of aa-tRNA to the A-site on the ribosome.

Escherichia coli↗
PubMed1995

Epidemiological survey of burns treated in Ankara, Turkey and desirable burn-prevention strategies.

From 1 January 1979 to 31 December 1993, 1109 patients were admitted to our burn unit located at Hacettepe University. Of the patients, 638 (57.5 per cent) were children (under the age of 16 years). The male to female ratio was 1.4:1 in children, and was approximately 2.6:1 for patients over 16 years of age. Of the 638 paediatric patients, 67 (10.5 per cent) sustained electrical burns. The causes of injury in the remaining 571 cases (89.5 per cent) were hot liquids in 379 (66.4 per cent of the non-electrical burns), flame in 190 (33.3 per cent) and contact burns in two (0.3 per cent). Of the scalds, 296 (78.1 per cent of the scalds), 52 (13.7 per cent), 22 (5.8 per cent) and nine (2.4 per cent) were caused by hot water, milk, meal and oil respectively. Of the flame burns, 21 (11.1 per cent) were due to LPG explosions. Of the 471 adult patients (over 16 years), 159 (33.8 per cent) were injured by electricity. The causes of non-electrical burn injuries were: hot liquid in 25, flame in 274, chemical agents in four, contact in four, and other causes in four. Although our centre is located in Central Anatolia, 41.8 per cent of all patients were referred from the other six regions of Turkey. Of the 1109 inpatients, 645 (58.2 per cent) were injured in Central Anatolia, 279 (25.2 per cent) in the Black Sea Region, 55 (5.0 per cent) in the Mediterranean Region, 18 (1.6 per cent) in the Marmara Region, 34 (3.1 per cent) in the Aegean Region, 52 (4.7 per cent) in Southeastern Anatolia and 26 (2.3 per cent) in Eastern Anatolia. Approximately two-thirds of the patients (419) required one or more surgical interventions, including debridement and grafting, as well as amputation. The most important early complications were acute renal failure (148 patients - 13.3 per cent), sepsis (660 patients - 59.5 per cent) and gastrointestinal haemorrhage (seven patients - 0.6 per cent). The overall mortality rate was 34.4 per cent. The epidemiological pattern of the burns showed that emergency measures should be taken to prevent scalding accidents to children throughout the country, and for electrical burns in adults, particularly those living in the Black Sea Region. In establishing, implementing and directing prevention programmes, regional differences should be taken into consideration.

Acute Kidney Injury↗
PubMed1994

Mutations in 23 S ribosomal RNA perturb transfer RNA selection and can lead to streptomycin dependence.

Escherichia coli ribosomes with a G to C transversion at position 2661 in 23 S ribosomal RNA are more accurate in tRNA selection than wild-type ribosomes. This enhanced accuracy is due to improved initial selection of ternary complexes rather than proofreading of aminoacyl tRNAs. The 2661C mutation reduces the binding rate of cognate ternary complexes to the A-site. This binding rate deficiency becomes dramatic when ribosomes also harbour an S12 mutation with a streptomycin-resistant, hyperaccurate phenotype. In this case, severe loss of kinetic efficiency in EF-Tu function leads to cell death. Streptomycin restores viability by increasing the association rate of ternary complex to these doubly altered ribosomes. The binding rate of EF-G to 2661C ribosomes is also reduced while the translocation rate is unaffected.

Escherichia coli↗