Transperineal omentum flap for the anatomic reconstruction of the rectovaginal space in the therapy of rectovaginal fistulas

AIM

Deep rectovaginal fistulas are a rare entity and pose a delicate challenge for the surgeon. The present study introduces different operative interventions involved in transperineal omental flap surgery.

METHOD

A retrospective analysis of all patients treated with a low or mid rectovaginal or enterovaginal fistula at the Department of Surgery of the University Hospital of Schleswig-Holstein, Campus Luebeck, was performed. Treatment results were discussed with respect to aetiology, localization, morbidity and outcome.

RESULTS

Between the years 2000 and 2010, a total of nine patients with a low or mid rectovaginal fistula were treated at our clinic. After local fistulectomy, all patients were additionally treated by a laparoscopically assisted omental flap reconstruction of the rectovaginal and perineal space. Eight of the nine patients received a protective ileostomy or colostomy. Only the patient with a history of Crohn's disease had no ileostomy raised. At a median follow-up of 22 months, no patient experienced recurrence of a rectovaginal fistula. Perioperative mortality was zero and minor complications were observed in 22%. Major complications were an anastomotic insufficiency after low anterior resection that was treated without further interventions. Another complication was a persistent fistula within the sphincter that needed re-operation and bovine plug repair combined with a mucosa flap.

CONCLUSIONS

Complete omental reconstruction of the rectovaginal space appears decisive in the operative therapy of deep rectovaginal or enterovaginal fistulas. Comparative studies on standard therapies are necessary although direct comparison of case series is difficult.

[Current state of laparoscopic hepatic surgery: results of a survey of DGAV-members]

BACKGROUND

To date laparoscopic hepatic surgery is only common in a few centres for a specific selected patient group. The intention of this survey was to estimate the current state of affairs for laparoscopic hepatic surgery in Germany at 2008.

MATERIALS AND METHODS

A questionnaire was prepared and sent out by e-mail in May 2009 to the members of the DGAV (German Society of General and Visceral Surgery). The feedback was evaluated anonymously.

RESULTS

A total of 181 answers were received by 31st July 2009 (return rate of 15.9%). The return rate of basic and standard care hospitals was 9.2%, specialized hospitals 23.6%, hospitals with maximum care 50% and university hospitals had a return rate of 71.9%. The question whether laparoscopic hepatic surgery had been performed in 2008 was answered with YES by 125 (69.1%) and NO by 54 (29.8%) members. The number of laparoscopic hepatic surgery interventions (laparoscopic ultrasound, laparoscopic radiofrequency ablation and resection) in 2008 was given as more than 50 by 4 (2.2%) hospitals, between 20 and 50 by 11 (6.1%) hospitals, between 10 and 20 by 23 (12.7%) hospitals, between 5 and 10 by 45 (24.9%) hospitals and between 0 and 5 by 54 (29.8%) hospitals. In 2008 the frequency of laparoscopic ultrasound during intraoperative staging to confirm the diagnosis ranged from 2 to 250, whereby 96.4% of the hospitals had less than 50 and only 2 hospitals (2.7%) had 211 and 250 examinations, respectively. 50 hospitals carried out laparoscopic radiofrequency ablation (RFA). 69 (38.1%) of the interviewed hospitals reported hepatic laparoscopic resections (n=551).

CONCLUSION

Laparoscopic liver surgery has been done in Germany in patients with benign or malignant liver lesions. Pure laparoscopy is the most common access. Atypical resections are the primarily indication followed by left lateral resections. All further types of resection have been done in a very small number. Laparoscopic liver surgery has been performed in all types of hospitals.

[Pneumoperitoneum in surgical management of giant scrotal hernias]

Surgical treatment of giant abdominal hernias includes reduction of the hernia content and tension-free closure of the abdominal wall. Initial laparoscopy simulates the postoperative abdominal wall tension. Recognizing the need for a preoperative pneumoperitoneum in cases of chronic eventration may help to avoid "abdominal catastrophes" including bowel resection, abdominal compartment, and extended abdominal wall reconstruction. We report a 66-year-old man with an asymptomatic long-standing giant scrotal hernia who was admitted with sepsis and uremia caused by intestinal obstruction.

[Secondary and primary prophylaxis of gastropathy associated with nonsteroidal antiinflammatory drugs or low-dose-aspirin: a review based on four clinical scenarios]

Based on current references four clinical scenarios were discussed and different management strategies were compared for secondary and primary prophylaxis of ulcer or peptic ulcer bleeding under continuous therapy with non-steroidal antiinflammatory drugs (NSAID) or low-dose-aspirin, for H.pylori-positive and H.pylori-negative patients. Used as secondary prophylaxis eradication alone is insufficient in preventing recurrent peptic ulcer or recurrent ulcer bleeding for H.pylori-positive patients who continue to take unselective NSAIDs. Maintenance therapy with PPIs or switching from nonselective NSAID to COX-2-inhibitors is required after eradication of H.pylori or primary H.pylori-negative patients. Further evaluation is needed of what kind of secondary prophylaxis - maintenance therapy with PPI or switching to COX-2-inhibitor - is more (cost-)effective. It is sufficient to use eradication of H.pylori alone as secondary prophylaxis in preventing recurrent peptic ulcer or recurrent ulcer bleeding for H.pylori-positive patients, who continue to take low-dose-aspirin. Maintenance therapy with PPI is not generally required. However it can be considered for patients with increased risk for gastrointestinal complications (previous history of peptic ulcer, age over 65 years, concomitant use of corticosteroids, anticoagulants or individual NSAID with higher risk for gastrointestinal complications, serious cardiovascular disease). Switching from low-dose-aspirin to clopidogrel is not required. Used as primary prophylaxis in preventing peptic ulcer or ulcer bleeding before starting long-term therapy with NSAIDs, COX-2-inhibitors or unselective NSAIDs concomitant with PPIs are recommended for patients with increased risk for gastrointestinal complications. Patients starting long-term therapy with unselective NSAIDs should be screened for H.pylori and eradicated. There are no valid data supporting screening for H.pylori and eradication for patients starting long-term therapy with low-dose-aspirin. Further studies are needed to evaluate a possible benefit for patients with increased risk for gastrointestinal complications.

[Primary renal hemangiosarcoma. Case report and review of the literature]

Primary hemangiosarcoma of the kidney is a very rare tumor for which only 23 case reports appear in the literature worldwide. An additional case of renal angiosarcoma in an adult is reported. The patient developed local tumor recurrence with multiple metastases within 4 weeks and died although there was no evidence of metastases at the time of nephrectomy.

Exploring the minimal substrate requirements for trans-cleavage by RNase P holoenzymes from Escherichia coli and Bacillus subtilis

We analysed the processing of small bipartite model substrates by Escherichia coli and Bacillus subtilis RNase P and corresponding hybrid enzymes. We demonstrate specific trans-cleavage of a model substrate with a 4 bp stem and a 1 nucleotide (nt) 5' flank, representing to date the smallest mimic of a natural RNase P substrate that could be processed in trans at the canonical RNase P cleavage site. Processing efficiencies decreased up to 5000-fold when the 5' flank was shortened from 3 to 1 nt. Reduction of the 5' flank to 1 nt was more deleterious than reducing the stem from 7 to 4 bp, although the 4 bp duplex formed only transiently, in contrast to the stable 7 bp duplex. These results indicate that the crucial contribution of nt -2 in the single-stranded 5' flank to productive interaction is a general feature of A- and B-type bacterial RNase P enzymes. We also showed that an Rp-phosphorothioate modification at nt -2 interferes with processing. Bacterial RNase P holoenzymes are also capable of cleaving single-stranded RNA oligonucleotides as short as 5 nt, yielding RNase P-specific 5'-phosphate and 3'-OH termini, with measured turnover rates of up to 0.7 min-1. All cleavage sites were at least 2 nt away from the 5' and 3' ends of the oligonucleotides. Some cleavage site preferences were observed dependent on the identity of the RNase P RNA subunit.

Correlation between processing efficiency for ribonuclease P minimal substrates and conformation of the nucleotide -1 at the cleavage position

It is demonstrated that acceptor stem duplexes derived from native tRNAs which contain a three-nucleotide extension at the 5'-terminus of mature tRNA are minimal substrates for ribonuclease P from both Escherichia coli and Bacillus subtilis. Variants with a cytidine at position -1 are most efficiently processed whereas the G -1 variant represents a comparatively poor substrate. An A -1 acceptor stem variant is a slightly better substrate than the G -1 variant though generally distinctly less efficient than the C -1 duplex. This is in qualitative agreement with the frequency of the occurrence of the corresponding nucleotides at position -1 in natural substrates, which is highest for pyrimidines and least for G. NMR analyses of the corresponding acceptor stems reveal that the conformation of the nucleotides at position -1 correlates with the substrate preferences of Ribonuclease P: Whereas C -1 adopts a conformation characterized by a glycosidic angle in the anti range (close to high-anti), the G -1 is clearly in syn conformation, and that of A -1 is intermediate between high-anti and syn. The riboses of nucleotides -1 are in all cases predominantly 2'-endo puckered.

DNA-binding of phenylalanyl-tRNA synthetase is accompanied by loop formation of the double-stranded DNA

The phenylalanyl-tRNA synthetase (FRS) from Thermus thermophilus has previously been shown to bind DNA. We demonstrate that the "winged" helix-turn-helix motifs in the duplicate domains B5 are the relevant structural elements for this DNA-binding property. By altering particular amino acids in the "wing", the affinity of the FRS to DNA was significantly reduced. Based on experimental data, which indicate that the FRS prefers a certain DNA structure rather than a particular consensus sequence, we propose a novel loop model for the DNA-binding mode of the FRS. In our model we assume that two segments of the same DNA molecule are bound simultaneously by both B5 domains and are aligned in parallel, while the intervening DNA forms a loop. Due to the limited flexibility of the DNA, loop formation is only possible if the respective intervening DNA stretch exceeds a certain length. Several lines of evidence support this model. (1) We demonstrate by gel retardation assays that the DNA requires a minimal number of ca 80 base-pairs to be bound by the FRS. (2) In the presence of the FRS, DNA longer than ca 80 base-pairs has a significantly increased DNase I accessibility. This agrees well with its known preferential cleavage at positions where the minor grove is on the outside of looped-out DNA molecules. (3) The initial cleavage by DNase I of >80 bp long DNA occurs in the middle of the fragment. In a looped molecule this is the position with the highest accessibility to DNase I. The function of the FRS related to DNA binding is still unknown. Since the FRS exists in the nucleus of rapidly growing mammalian cells, and protein-induced DNA bending or looping contributes to several transcription, replication, and recombination systems in both prokaryotes and eukaryotes, it is likely that the FRS, in addition to its aminoacylation function, influences common cellular processes via DNA binding.

NMR spectroscopic evidence for Mn(2+)(Mg(2+)) binding to a precursor-tRNA microhelix near the potential RNase P cleavage site

The binding of Mg(2+)/Mn(2+) to acceptor stem microhelices as minimal models for precursor-tRNA(Gly) is demonstrated by NMR spectroscopy. From the evaluation of COSY and NOESY spectra, binding sites for Mg(2+)/Mn(2+) can be inferred. In particular, one binding site exists near the ribose moiety of nucleotide -1 at the position of cleavage by RNase P. From comparison with a variant possessing a deoxynucleotide at this position, it is concluded that the 2'-OH group of this nucleotide is indispensable for coordinating the divalent metal ion. Hence, this catalytically important metal ion is "pre-bound" to the precursor-tRNA before complexation with RNase P.

Interaction of fMet-tRNAfMet and fMet-AMP with the C-terminal domain of Thermus thermophilus translation initiation factor 2

Two polypeptides resistant against proteolytic digestion were identified in Thermus thermophilus translation initiation factor 2 (IF2): the central part of the protein (domains II/III), and the C-terminal domain (domain IV). The interaction of intact IF2 and the isolated proteolytic fragments with fMet-tRNAfMet was subsequently characterized. The isolated C-terminal domain was as effective in binding of the 3' end of fMet-tRNAf Met as intact IF2. N-Formylation of Met-tRNAfMet was required for its efficient binding to the C-terminal domain. This suggests that the interaction between the C-terminal domain and the 3' end of fMet-tRNAfMet is responsible for the recognition of fMet-tRNAfMet by IF2 during translation initiation. Moreover, it was demonstrated that fMet-AMP is a minimal ligand of IF2. fMet-AMP inhibits fMet-tRNAfMet binding to IF2 as well as the activity of IF2 in the stimulation of ApUpG-dependent ribosomal binding of fMet-tRNAf Met. Specific interaction of fMet-AMP with IF2 was demonstrated by 1H-NMR spectroscopy. These findings indicate that fMet-AMP and the 3' terminal fMet-adenosine of fMet-tRNAfMet use the same binding site on the C-terminal domain of IF2 and imply that the interaction between the C-terminal domain and the 3' end of fMet-tRNAfMet is primarily responsible for the fMet-tRNAfMet binding and recognition by IF2.

The C-A mismatch base pair and the single-strand terminus in the E. coli initiator tRNA(fMet) acceptor stem adopt unusual conformations

Acceptor stem variants of tRNA(fMet) (Escherichia coli) have been characterized by nuclear magnetic resonance. The wild type contains a C1-A72 mismatch pair which is crucial for its biological function. For comparison, the mismatch was replaced by regular pairs U1-A72 and C1-G72. Further variants contain an altered discriminator base, G73, or a G1-C72/U73 combination. The stems of variants U1-A72/A73 and C1-G72/A73 have A-RNA geometry, which extends essentially to the single-strand terminus. C1-A72/G73 variant and wild type are structurally almost identical. C1 and A72 adopt peculiar conformations with C1 being largely destacked with respect to G2, while A73 stacks upon C1. The unique arrangement of the mismatch causes a distinctly different orientation of the single-strand terminus compared to variants with regular 1-72 base pairs, and to formyltransferase-complexed tRNA(fMet).

Dimerization of double-stranded RNA possessing a 3'-overhanging single-stranded end

A simple system derived from the acceptor stem of tRNA(Ala) is presented which undergoes a pH-dependent dimerization. This is brought about by formation of C+-G-C base triples of the pyrimidine motif type between protonated cytidines of the 3' single-stranded end and regularly paired G-C pairs in the double-helical stem. In addition, an unusual interaction between a protonated adenine and a regular G-C pair is suggested. The equilibrium between monomer and dimer forms can be monitored via NMR spectroscopy and UV melting curve analysis. A dimerization enthalpy of 159 kJ mol(-1) was found at pH 5.0. The system could serve as a model for inter- and intra-molecular association, respectively, of single-stranded and double-helical regions to enable optimal packing of large RNA molecules.

Secondary structure dimorphism and interconversion between hairpin and duplex form of oligoribonucleotides

RNA hairpins can alternatively form a dimer with a bulged loop flanked by regularly base paired regions. [1H]NMR spectroscopy and native gel electrophoresis were used to study how the sequence of nucleotides in the loop of the hairpin affect the hairpin-duplex interconversion. As a model system, a hairpin containing 7 nucleotides in the loop and 5 base pairs in the stem was used. The loop size was gradually reduced from 7 to 4 nucleotides, yielding finally the stable UNCG tetraloop. Single nucleotide mutations were performed to investigate the influence of the self-complementarity of the loop sequence on the dimerization. The results demonstrate that (1) the initial fraction of hairpin is determined by concentration of the oligonucleotide, the annealing procedure, and the relative stability of the loop, (2) the degree of self-complementarity of the loop sequence of the hairpin governs the dimerization kinetics, and (3) oligonucleotides complementary to the loop sequence decrease the dimerization rate. We propose a secondary structure-based model for the dimerization reaction of RNA hairpins in which the formation of intermolecular base pairs between self-complementary nucleotides of the loops represents the nucleation step.

NMR study on the impact of metal ion binding and deoxynucleotide substitution upon local structure and stability of a small ribozyme

We have studied a very small ribozyme described earlier which requires the presence of soft metal ions like manganese or cadmium. It consists of only three uridines as ribozyme, cleaving the sequence 5'-GAAA-3' after the guanosine. We have set out to characterize the metal ion binding in this system by NMR spectroscopy and the impact of the ribose 2'-OH group of the cleavable nucleotide upon local structure. NMR results indicate a high degree of regularity and order in the pyrimidine-rich ribozyme strand, and high flexibility within the purine-rich substrate. The guanosine 2'-hydroxy group adjacent to the cleavage site was found to have a profound effect upon the structure, apparently destabilizing a stacked arrangement. Metal ions were found to bind in a rather unspecific way, however, in the presence of higher amounts of divalent ions a preference in the vicinity of the cleavage site could be observed. 113Cd NMR spectra suggest a specific binding of Cd2+ ions to the RNA.

Structural and dynamic helix geometry alterations induced by mismatch base pairs in double-helical RNA

A ribooligonucleotide microhelix derived from the acceptor stem of Escherichia coli tRNA(Ala) having a C3-A70 mismatch in place of the G3-U70 wobble pair in the wild-type tRNA(Ala), and a sequence variant with a regular U3-A70 base pair have been investigated by NMR. In vivo, suppressor tRNA(Ala) variants with C3-A70 (as well as several other) mismatch pairs are substrates for alanyl-tRNA synthetase (ARS), supporting the hypothesis of an 'indirect' recognition of the identity element 3-70 mismatch pair via structural modifications caused by the mispair in comparison to canonical A-RNA helices. It is demonstrated that the C-A mismatch likewise induces helix geometry alterations, in particular with respect to base stacking in the vicinity of the mismatch. However, with reference to the 'wild-type' G3-U70 microhelix, destacking in the C3-A70 acceptor stem duplex occurs in the opposite direction from the mismatch pair. Therefore it is concluded that the locally enhanced conformational flexibility or dynamics associated with the structural changes induced by the mismatch pairs could be an essential prerequisite for optimal adaptation of the tRNA(Ala) acceptor stem to the contact region of the ARS.

Ni2+-binding RNA motifs with an asymmetric purine-rich internal loop and a G-A base pair

RNA molecules with high affinity for immobilized Ni2+ were isolated from an RNA pool with 50 randomized positions by in vitro selection-amplification. The selected RNAs preferentially bind Ni2+ and Co2+ over other cations from first series transition metals. Conserved structure motifs, comprising about 15 nt, were identified that are likely to represent the Ni2+ binding sites. Two conserved motifs contain an asymmetric purine-rich internal loop and probably a mismatch G-A base pair. The structure of one of these motifs was studied with proton NMR spectroscopy and formation of the G-A pair at the junction of helix and internal loop was demonstrated. Using Ni2+ as a paramagnetic probe, a divalent metal ion binding site near this G-A base pair was identified. Ni2+ ions bound to this motif exert a specific stabilization effect. We propose that small asymmetric purine-rich loops that contain a G-A interaction may represent a divalent metal ion binding site in RNA.

A biologically active 53 kDa fragment of overproduced alanyl-tRNA synthetase from Thermus thermophilus HB8 specifically interacts with tRNA Ala acceptor helix

The alaS gene encoding the alanyl-tRNA synthetase (AlaRS) from Thermus thermophilus HB8 was cloned and sequenced. The gene comprises 2646 bp, corresponding to 882 amino acids, 45% of which are identical to the enzyme from Escherichia coli . The T. thermophilus AlaRS was overproduced in E.coli , purified and characterized. It has high thermal stability up to approximately 65 degrees C, with a temperature optimum of aminoacylation activity at approximately 60 degrees C, and will be valuable for crystallization. The purified enzyme appears as a dimer with a specific activity of 220 U/mg and k cat/ K M values of 118 000/s/M for alanine and 114 000/s/M for ATP. By genetic engineering a 53 kDa fragment of AlaRS comprising the N-terminal 470 amino acids (AlaN470) was also overproduced and purified. It is as stable as entire AlaRS and sufficient for specific aminoacylation of intact tRNAAla, as well as acceptor stem microhelices with a G3-U70, but not U3-A70, I3-U70 or C3-U70, base pair. The reduced binding strength of such microhelices to AlaN470 enabled, due to the resulting fast exchange of the microhelices between free and complexed states, preliminary NMR analyses of the binding mode and intermolecular recognition.

Interaction of N-tosyl-L-phenylalanylchloromethane with Thermus thermophilus elongation factor Tu

The interaction of N-tosyl-L-phenylalanylchloromethane (TosPheCH2Cl) with Thermus thermophilus elongation factor Tu (EF-Tu) was studied by affinity labelling and NMR spectroscopy. TosPheCH2Cl binds to GDP and GTP conformers of EF-Tu. The interaction of TosPheCH2Cl with EF-Tu x GDP leads to alkylation of Cys82, while interaction of TosPheCH2Cl with EF-Tu x GTP does not lead to covalent labelling. [A82]EF-Tu, in which the Cys82 is replaced by Ala, has similar properties to wild-type EF-Tu with respect to GTPase activity, binding of guanine nucleotides, interaction with elongation factor Ts (EF-Ts) and interaction with ribosomes. This structural change did not lead to changes, compared with wild-type EF-Tu in the functionality of [A82]EF-Tu, either in the GTP or in the GDP conformation. TosPheCH2Cl binds to EF-Tu x GTP with a dissociation constant of 10 microM. The interaction of TosPheCH2Cl with EF-Tu promotes the hydration of the carbonyl group of TosPheCH2Cl. TosPheCH2Cl competes with aminoacyl-tRNA for its binding site on EF-Tu x GTP. Covalent modification of Cys82 by TosPheCH2Cl does not prevent nucleotide binding and GTPase activity, but interferes with the interaction with aminoacyl-tRNA. TosPheCH2Cl probably mimics the aminoacyl residue of the aminoacyl-tRNA and binds to its binding site on EF-Tu x GTP. This rather specific interaction with EF-Tu x GTP does not allow the modification of Cys82, whereas the loose interaction of TosPheCH2Cl with EF-Tu x GDP leads to alkylation of this residue.

The structure of 3'-O-anthraniloyladenosine, an analogue of the 3'-end of aminoacyl-tRNA

3'-O-Anthraniloyladenosine, an analogue of the 3'- terminal aminoacyladenosine residue in aminoacyl-tRNAs, was prepared by chemical synthesis, and its crystal structure was determined. The sugar pucker of 3'-O-anthraniloyladenosine is 2'-endo resulting in a 3'-axial position of the anthraniloyl residue. The nucleoside is insynconformation, which is stabilized by alternating stacking of adenine and benzoyl residues of the neighboring molecules in the crystal lattice. The conformation of the 5'-hydroxymethylene in 3'-O- anthraniloyladenosine is gauche-gauche. There are two intramolecular and two intermolecular hydrogen bonds and several H-bridges with surrounding water molecules. The predominant structure of 3'-O-anthraniloyladenosine in solution, as determined by NMR spectroscopy, is 2'-endo,gauche-gauche and anti for the sugar ring pucker, the torsion angle around the C4'-C5'bond and the torsion angle around the C1'-N9 bond, respectively. The 2'-endo conformation of the ribose in 2'(3')-O-aminoacyladenosine, which places the adenine and aminoacyl residues in equatorial and axial positions, respectively, could serve as a structural element that is recognized by enzymes that interact with aminoacyl-tRNA or by ribosomes to differentiate between aminoacylated and non-aminoacylated tRNA.

NMR evidence for helix geometry modifications by a G-U wobble base pair in the acceptor arm of E. coli tRNA(Ala)

A ribooligonucleotide duplex representing the acceptor stem of E. coli RNA(Ala) with a G3-U70 wobble base pair, which is the main identity element for the recognition by the alanine-tRNA synthetase, has been characterized by 2D-NMR, as having two sequence variants with a regular Watson-Crick G3-C70 and an I3-U70 wobble pair, respectively. As compared to a regular A-RNA, the G-U base pair gives rise to variations of the local helix geometry which are reflected in distinct local chemical shift changes. Structural differences between the duplex possessing an I3-U70 base pair and the wild-type G3-U70 sequence have also been found. The nucleotides in the ubiquitous single-stranded NCCA terminus display a surprisingly high degree of stacking order, especially between A73, C74, and C75.

[Risk score and postoperative complications in pediatric surgery]

We have developed a risk score meeting the special demands of pediatric surgery. It conveys an objective impression of the patients' preoperative condition and enables us to predict their individual intra- and postoperative behavior. This study compiles the course of 1425 operations carried out between 1986 and 1990. They were divided into low, intermediate and high risk. In addition, the patients were classified into six different age groups. We demonstrate that the number of points assigned by our risk score is highly correlated with the rate of complications that occurred, that accompanying malformations and diseases are correctly picked up and weighed by the score as far as their importance for the postoperative course is concerned, that the score is suitable for ascertaining which patients have a high probability of developing complications: the specificity is close to 100% for more than 12 points on the score, and the proportion of correctly predicted lethal courses (sensitivity) is also close to 100%. The significance of the risk score lies first in the possibility of giving patients exact data on the intra- and postoperative risk, and secondly in the provision of an objective measure of quality control--which is legally prescribed in Germany--and comparison with other hospitals. Third, the risk score gives clear starting points for research aiming at improvement in the field of surgery in sick children, and lastly it forms the basis for reliable preoperative recognition of high-risk as needed patients for modern payment methodology of the per-cose costs and thus makes it possible to charge accordingly.

Effector region of the translation elongation factor EF-Tu.GTP complex stabilizes an orthoester acid intermediate structure of aminoacyl-tRNA in a ternary complex

tRNA(Val) from Escherichia coli was aminoacylated with [1-13C]valine and its complex with Thermus thermophilus elongation factor EF-Tu.GTP was analyzed by 13C NMR spectroscopy. The results suggest that the aminoacyl residue of the valyl-tRNA in ternary complex with bacterial EF-Tu and GTP is not attached to tRNA by a regular ester bond to either a 2'- or 3'-hydroxyl group; instead, an intermediate orthoester acid structure with covalent linkage to both vicinal hydroxyls of the terminal adenosine-76 is formed. Mutation of arginine-59 located in the effector region of EF-Tu, a conserved residue in protein elongation factors and the alpha subunits of heterotrimeric guanine nucleotide-binding regulatory proteins (G proteins), abolishes the stabilization of the orthoester acid structure of aminoacyl-tRNA.

[Mortality and postoperative cause of death in pediatric surgery]

We analysed our patients in pediatric surgery from 1959 to 1990 in regard to post-operative causes of death according to the Petren scheme. "Post-operative infection" as a cause of death dropped from 45% to 2%, "post-operative pneumonia" from 10% to 4%. Death due to accompanying congenital defects has increased from 3% to 15%. The cause of death "main disease" remained the same with 18%. Post-operative causes of death due to wrong diagnoses ranged at 2%, wrong treatment as cause of death decreased from 18% to 4%. In the 41 years' range of our survey, 115,598 children were operated as in-patients. During the first 5-year-period postoperative mortality was 2.2%, during the last 5-year-period 0.12%.

Proton NMR studies of manganese ion binding to tRNA-derived acceptor arm duplexes

Several RNA duplexes corresponding to the acceptor arms of different tRNAs have been analyzed with respect to their divalent metal ion binding capability by means of proton NMR spectroscopy using paramagnetic Mn2+ ions as probes. In particular, the role of GU wobble base pairs has been analyzed with reference to their potential for creating metal ion binding sites. It is shown that both the structural modifications induced by GU pairs in the A-RNA geometry and the sequence context seem to affect the metal ion binding capabilities.

The 3'-terminal end (NCCA) of tRNA determines the structure and stability of the aminoacyl acceptor stem

We have done a systematic study on the contribution of the single-stranded NCCA end (where N is any nucleotide) to the stability of the aminoacyl stem of tRNA. A 7-bp RNA duplex with the single-strand ACCA 3' terminus derived from the aminoacyl stem of Escherichia coli tRNA(Ala) and several chemically synthesized sequence variants are characterized by proton NMR and thermodynamic parameters. The single-stranded 3' terminus noticeably stabilizes the duplex in a sequence-dependent manner. Though the largest contribution to the stability gain due to the ACCA end is provided by the first dangling 3' nucleotide, the influence of even the fourth nucleotide is measurable. The nature of the N73 discriminator base influences the stem structure and stability, which may be important for the recognition of tRNA by aminoacyl-tRNA synthetase. The stepwise attachment of the nucleotides to the 3' tail improves the stacking of the unpaired bases over the helix stem. Hence, the ACCA end appears to be structured. Replacing Mg2+ with Mn2+ causes broadening of certain imino proton peaks in the NMR spectrum, indicating a specific divalent metal ion binding site in the vicinity of the major identity element of the duplex (G3-U70) that is required for its recognition by the Ala-tRNA synthetase.

Nucleotide binding and GTP hydrolysis by the 21-kDa product of the c-H-ras gene as monitored by proton-NMR spectroscopy

Proton-NMR signals in the downfield region (below approximately 10 ppm) have been shown to provide a useful spectroscopic window to monitor the binding of guanine nucleotides to the active site of GTP/GDP-binding proteins via H-bonds, as specified here by the 21-kDa product of the c-H-ras gene (p21). The time course of the intensity change of certain peaks upon addition of GTP to nucleotide-free p21 corresponds to the GTP hydrolysis rate as determined by HPLC. Though there are fewer potential H-bond acceptors in the GDP-bound protein than in the GTP complex, more downfield peaks are found in the former complex, suggesting tighter binding of GDP. Moreover, inspection of the downfield proton-NMR spectra permits rapid detection of subtle changes of the active site induced by complexation with slowly hydrolyzing GTP analogues resulting from mutations of the amino acid sequence, especially in the phosphate binding loop. Our studies strongly suggest that no major conformational change of the phosphate-binding region occurs upon nucleotide complexation that precedes the catalytic step. Besides, it is suspected that the Ser17 hydroxyl group is involved in nucleotide binding and GTP hydrolysis.

Ternary complex between elongation factor Tu.GTP and Phe-tRNA(Phe)

The effect of aminoacylation and ternary complex formation with elongation factor Tu.GTP on the tertiary structure of yeast tRNA(Phe) was examined by 1H-NMR spectroscopy. Esterification of phenylalanine to tRNA(Phe) does not lead to changes with respect to the secondary and tertiary base pair interactions of tRNA. Complex formation of Phe-tRNA(Phe) with elongation factor Tu.GTP results in a broadening of all imino proton resonances of the tRNA. The chemical shifts of several NH proton resonances are slightly changed as compared to free tRNA, indicating a minor conformational rearrangement of Phe-tRNA(Phe) upon binding to elongation factor Tu.GTP. All NH proton resonances corresponding to the secondary and tertiary base pairs of tRNA, except those arising from the first three base pairs in the aminoacyl stem, are detectable in the Phe-tRNA(Phe)-elongation factor Tu-GTP ternary complex. Thus, although the interactions between elongation factor Tu and tRNA accelerate the rate of NH proton exchange in the aminoacyl stem-region, the Phe-tRNA(Phe) preserves its typical L-shaped tertiary structure in the complex. At high (> 10(-4) M) ligand concentrations a complex between tRNA(Phe) and elongation factor Tu-GDP can be detected on the NMR time-scale. Formation of this complex is inhibited by the presence of any RNA not related to the tRNA structure. Using the known tertiary structures of yeast tRNA(Phe) and Thermus thermophilus elongation factor Tu in its active, GTP form, a model of the ternary complex was constructed.

Nucleotide binding and GTP hydrolysis by elongation factor Tu from Thermus thermophilus as monitored by proton NMR

Proton NMR experiments of the GTP/GDP-binding protein EF-Tu from the extremely thermophilic bacterium Thermus thermophilus HB8 in H2O have been performed paying special attention to the resonances in the downfield region (below 10 ppm). Most of these downfield signals are due to hydrogen bonds formed between the protein and the bound nucleotide. However, three downfield resonances appear even in the nucleotide-free EF-Tu. The middle and C-terminal domain (domain II/III) of EF-Tu lacking the GTP/GDP-binding domain gives rise to an NMR spectrum that hints at a well-structured protein. In contrast to native EF-Tu, the domain II/III spectrum contains no resonances in the downfield region. Several downfield resonances can be used as a fingerprint to trace hydrolysis of protein-bound GTP and temperature effects on the EF-Tu.GDP spectra. NMR studies of the binding of guanosine nucleotide analogues (GMPPNP, GMPPCP) to nucleotide-free EF-Tu have been carried out. The downfield resonances of these complexes differ from the spectrum of EF-Tu.GTP. Protected and photolabile caged GTP was bound to EF-Tu, and NMR spectra before and after photolysis were recorded. The progress of the GTP hydrolysis could be monitored using this method. The downfield resonances have been tentatively assigned taking into account the known structural and biochemical aspects of EF-Tu nucleotide-binding site.

[PAF-antagonists with a phospholipid structure. 1. Phospholipids with hetero-arene head groups: synthesis, characterization and determination of the action of structural elements]

A series of analogues of platelet-activating factor (PAF) with heteroarene head groups have been synthesized, and tested for biological activities on blood platelets in vitro. In comparison with PAF most of the structural modifications exerted weak proaggregatory effects. The 4-(dimethylamino)pyridinium compound did not activate platelets but inhibited selectively PAF-induced platelet responses. These results point to a crucial role of the distance between the phosphoryl group and polar head for expression of PAF-antagonistic properties. Structural features of PAF-antagonist have been investigated by two-dimensional proton NMR spectroscopy, and proposed a model with three-dimensional structure.