The crystal structure of EcoRV endonuclease and of its complexes with cognate and non-cognate DNA fragments.

The crystal structure of EcoRV endonuclease has been determined at 2.5 A resolution and that of its complexes with the cognate DNA decamer GGGATATCCC (recognition sequence underlined) and the non-cognate DNA octamer CGAGCTCG at 3.0 A resolution. Two octamer duplexes of the non-cognate DNA, stacked end-to-end, are bound to the dimeric enzyme in B-DNA-like conformations. The protein--DNA interactions of this complex are prototypic for non-specific DNA binding. In contrast, only one cognate decamer duplex is bound and deviates considerably from canonical B-form DNA. Most notably, a kink of approximately 50 degrees is observed at the central TA step with a concomitant compression of the major groove. Base-specific hydrogen bonds between the enzyme and the recognition base pairs occur exclusively in the major groove. These interactions appear highly co-operative as they are all made through one short surface loop comprising residues 182-186. Numerous contacts with the sugar phosphate backbone extending beyond the recognition sequence are observed in both types of complex. However, the total surface area buried on complex formation is > 1800 A2 larger in the case of cognate DNA binding. Two acidic side chains, Asp74 and Asp90, are close to the reactive phosphodiester group in the cognate complex and most probably provide oxygen ligands for binding the essential cofactor Mg2+. An important role is also indicated for Lys92, which together with the two acidic functions appears to be conserved in the otherwise unrelated structure of EcoRI endonuclease. The structural results give new insight into the physical basis of the remarkable sequence specificity of this enzyme.     

Efficient random subcloning of DNA sheared in a recirculating point-sink flow system.

Based on a high-performance liquid chromatographic pump, we have built a device that allows recirculation of DNA through a 63-microm orifice with ensuing fractionation to a minimum fragment size of approximately 300 base pairs. Residence time of the DNA fragments in the converging flow created by a sudden contraction was found to be sufficiently long to allow extension of the DNA molecules into a highly extended conformation and, hence, breakage to occur at midpoint. In most instances, 30 passages sufficed to obtain a narrow size distribution, with >90% of the fragments lying within a 2-fold size distribution. The shear rate required to achieve breakage was found to be inversely proportional to the 1.0 power of the molecular weight. Compared with a restriction digest, up to 40% of all fragments could be cloned directly, with only marginal improvements in cloning efficiency having been observed upon prior end repair with Klenow, T4 polymerase or T4 polynucleotide kinase. Sequencing revealed a fairly random distribution of the fragments.     

Crystal structure of human platelet-derived growth factor BB.

The crystal structure of the homodimeric BB isoform of human recombinant platelet-derived growth factor (PDGF-BB) has been determined by X-ray analysis to 3.0 A resolution. The polypeptide chain is folded into two highly twisted antiparallel pairs of beta-strands and contains an unusual knotted arrangement of three intramolecular disulfide bonds. Dimerization leads to the clustering of three surface loops at each end of the elongated dimer, which most probably form the receptor recognition sites.     

Re-sequencing of multiple single nucleotide polymorphisms by liquid chromatography–electrospray ionization mass spectrometry

Allelic discrimination of single nucleotide polymorphisms (SNPs) and, particularly, determination of the phase of multiple variations are of utmost importance in genetics. The physicochemical separation of alleles by completely denaturing ion-pair reversed-phase high-performance liquid chromatography and their on-line sequence determination by electrospray ionization mass spectrometry is demonstrated. Simultaneous genotyping of two and three simple sequence polymorphisms contained within 73–114 bp was accomplished with low femtomolar amounts of unpurified amplicons from polymerase chain reaction. Determination of allelic composition is enabled by the high accuracy (better than 0.019%) of intact mass measurements or by comparative sequencing using gas-phase fragmentation and tandem mass spectrometry in combination with fully automated, computer-aided data interpretation.     

Urinary amino acid analysis: A comparison of iTRAQ®–LC–MS/MS,GC–MS,and amino acid analyzer

Urinary amino acid analysis is typically done by cation-exchange chromatography followed by post-column derivatization with ninhydrin and UV detection. This method lacks throughput and specificity. Two recently introduced stable isotope ratio mass spectrometric methods promise to overcome those shortcomings. Using two blinded sets of urine replicates and a certified amino acid standard, we compared the precision and accuracy of gas chromatography/mass spectrometry (GC–MS) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) of propyl chloroformate and iTRAQ^® derivatized amino acids, respectively, to conventional amino acid analysis. The GC–MS method builds on the direct derivatization of amino acids in diluted urine with propyl chloroformate, GC separation and mass spectrometric quantification of derivatives using stable isotope labeled standards. The LC–MS/MS method requires prior urinary protein precipitation followed by labeling of urinary and standard amino acids with iTRAQ^® tags containing different cleavable reporter ions distinguishable by MS/MS fragmentation. Means and standard deviations of percent technical error (%TE) computed for 20 amino acids determined by amino acid analyzer, GC–MS, and iTRAQ^®–LC–MS/MS analyses of 33 duplicate and triplicate urine specimens were 7.27 ± 5.22, 21.18 ± 10.94, and 18.34 ± 14.67, respectively. Corresponding values for 13 amino acids determined in a second batch of 144 urine specimens measured in duplicate or triplicate were 8.39 ± 5.35, 6.23 ± 3.84, and 35.37 ± 29.42. Both GC–MS and iTRAQ^®–LC–MS/MS are suited for high-throughput amino acid analysis, with the former offering at present higher reproducibility and completely automated sample pretreatment, while the latter covers more amino acids and related amines.     

Expression and Function of Methylthioadenosine Phosphorylase in Chronic Liver Disease

To study expression and function of methylthioadenosine phosphorylase (MTAP), the rate-limiting enzyme in the methionine and adenine salvage pathway, in chronic liver disease.

Design

MTAP expression was analyzed by qRT-PCR, Western blot and immunohistochemical analysis. Levels of MTA were determined by liquid chromatography-tandem mass spectrometry.

Results

MTAP was downregulated in hepatocytes in murine fibrosis models and in patients with chronic liver disease, leading to a concomitant increase in MTA levels. In contrast, activated hepatic stellate cells (HSCs) showed strong MTAP expression in cirrhotic livers. However, also MTA levels in activated HSCs were significantly higher than in hepatocytes, and there was a significant correlation between MTA levels and collagen expression in diseased human liver tissue indicating that activated HSCs significantly contribute to elevated MTA in diseased livers. MTAP suppression by siRNA resulted in increased MTA levels, NFκB activation and apoptosis resistance, while overexpression of MTAP caused the opposite effects in HSCs. The anti-apoptotic effect of low MTAP expression and high MTA levels, respectively, was mediated by induced expression of survivin, while inhibition of survivin abolished the anti-apoptotic effect of MTA on HSCs. Treatment with a DNA demethylating agent induced MTAP and reduced survivin expression, while oxidative stress reduced MTAP levels but enhanced survivin expression in HSCs.

Conclusion

MTAP mediated regulation of MTA links polyamine metabolism with NFκB activation and apoptosis in HSCs. MTAP and MTAP modulating mechanisms appear as promising prognostic markers and therapeutic targets for hepatic fibrosis.     

Analysis of human urine reveals metabolic changes related to the development of acute kidney injury following cardiac surgery

Acute kidney injury (AKI) is a frequent complication of sepsis, major surgery or nephrotoxic medication use. It is associated with high morbidity and mortality. In an effort to identify novel biomarkers capable of predicting the development of AKI after cardiac surgery with cardiopulmonary bypass use, urine specimens were collected before and at 4 and 24 h after surgery from 106 patients and analyzed by means of nuclear magnetic resonance spectroscopy. Postoperative AKI of stage 1–3 as defined by the Acute Kidney Injury Network (AKIN) developed in 34 cases. Employing Quantile Normalization and support vector machine based classification, spectra of the 24-hour postoperative urine specimens were found to predict AKI across all stages with an average accuracy of 76.0 % and a corresponding area under the receiver operating characteristic curve of 0.83. Considering only AKIN-stage 2 and 3 patients, prediction accuracy increased to 81.7 % and 100 %, respectively. Among the small set of predictive biomarkers identified was carnitine, the urinary concentration of which was elevated significantly in AKI-free patients only, and tranexamic acid, which is routinely applied as an antifibrinolytic agent at the end of surgery, and whose renal excretion was delayed in AKI patients. The study underscores the power of NMR and bioinformatics in identifying novel biomarkers of disease and in gaining new insights into pathomechanisms.     

Multiplex analysis of single-nucleotide extension products on a 16-capillary,denaturing, high-performance liquid chromatography array

We constructed a high-performance liquid chromatography array consisting of 16 monolithic poly(styrene/divinylbenzene) capillaries for the parallel multiplex analysis of fluorescent dye-labeled single-nucleotide extension products. Because of the high chemical and physical robustness of the column bed that is covalently linked to the inner surface of the fused silica capillary, the array can be reused thousands of times without replenishment. The choice of fluorophore exerts a significant effect on resolution of the extension products. FAM, HEX, and TAMRA allowed complete resolution of all four possible allelic extension products not only from the extension primer but also from each other. The quantitative accuracy of the method enables the genetic typing of bi- and triallelic single-nucleotide polymorphisms in polyploid genomes and pooled samples.