Mutational analysis of human glutathione transferase A2-2 identifies structural elements supporting high activity with the prodrug azathioprine

Glutathione transferase (GST) A2-2 is the human enzyme displaying the highest catalytic activity with the prodrug azathioprine (Aza). The reaction releases pharmacologically active 6-mercaptopurine by displacing the imidazole moiety from the Aza molecule. The GST-catalyzed reaction is of medical significance, since high rates of Aza activation may lead to adverse side effects in treated patients. The present study involves structure-activity relationships in GST A2-2 variants. Chimeric GSTs were previously generated by DNA shuffling and two peptide segments, one N-terminal and one C-terminal, were identified as primary determinants of Aza activity. The segments contain several residues of the substrate-binding H-site and their significance for supporting high Aza activity was investigated. Substitution of the corresponding two small regions in the low-activity human GST A3-3 or rat GST A3-3 by the human GST A2-2 segments generated chimeras with ～10-fold enhanced Aza activity. The H-site residues Met208 and Leu213 in the C-terminal segment of GST A2-2 were mutated to produce a library with all possible residue combinations. At a calculated 93% library coverage, all of the 1880 mutants examined showed wild-type or decreased Aza activity, even though some retained activities with alternative substrates, further emphasizing the importance of this region for the targeted activity.     

Proposed dairy calf birth certificate data and death loss categorization scheme

The majority of dairy heifer calves in the United States are destined to be dairy replacements. However, many dairy heifer and bull calves die before 6 mo of age. Of these calves, about 6% (more than 500,000 calves) die at birth or shortly after (i.e., currently termed “stillbirth”). An additional 6% of dairy heifers die during the preweaning period. Death loss in dairy calves is primarily due to stillbirths, failure to adapt to extrauterine life, and infectious disease processes. The reasons for preweaning heifer calf deaths caused by infectious diseases are generally categorized based on easily recognizable clinical signs such as digestive disease/scours or respiratory disease. Most causes of calf death can be mitigated by appropriate preventive care or well-tailored treatments, meaning that the typical death loss percentage could be decreased with better management. Producers could gather information on the circumstances near birth and at death if they had appropriate guidance on what details to record and monitor. This paper provides recommendations on data to collect at the time of birth (i.e., calf birth certificate data). The recording of these critical pieces of information is valuable in evaluating trends over time in morbidity and mortality events in dairy calves. Ideally, necropsy examination would substantially improve the identification of cause of death, but even without necropsy, attribution of cause of death can be improved by more carefully defining death loss categories in on-farm record systems. We propose a death loss categorization scheme that more clearly delineates causes of death. Recommendations are provided for additional data to be collected at the time of death. Recording and analyzing birth certificate and death loss data will allow producers and veterinarians to better evaluate associations between calf risk factors and death, with the goal of reducing dairy calf mortality.     

Detection of Damage in Assembled Rolling Element Bearings

A nondestructive method, capable of detecting localized surface damage, such as small spalls, nicks, dents and scratches, on the balls (rollers) and races of assembled rolling-element bearings, is discussed. The method utilizes the “almost periodical” character of vibration peaks produced by rotating a damaged bearing at constant speed. These “almost periodical” peaks are compared to the random vibration peaks, generated by the undamaged portions of the rolling surfaces of the bearing. Instrumentation to accomplish this comparison is described. It includes a vibration test spindle with pickup and amplifier, electronic gating circuitry serving as frequency and phase discriminator, and electronic counters to count “almost periodic” and random vibration peaks. Different methods of interpreting the counts and evaluating the degree of bearing damage are discussed.     

Contribution of display size to speech intelligibility in videophone systems

Widespread use of videophones has been limited due to cost factors and human factors. If demands for image size and quality were relaxed while preserving the communicational value added by visual data, low end videophones may become feasible. After a review of pertinent research, we describe an experiment indicating modest visual augmentation significantly aids speech intelligibility. The results suggest several directions for further research.     

Substrate Conformations Set the Rate of Enzymatic Acrylation by Lipases

Acrylates represent a class of α,β‐unsaturated compounds of high industrial importance. We investigated the influence of substrate conformations on the experimentally determined reaction rates of the enzyme‐catalysed transacylation of methyl acrylate and derivatives by ab initio DFT B3LYP calculations and molecular dynamics simulations. The results supported a least‐motion mechanism upon the sp² to sp³ substrate transition to reach the transition state in the enzyme active site. This was in accordance with our hypothesis that acrylates form productive transition states from their low‐energy s‐sis/s‐trans conformations. Apparent k_cat values were measured for Candida antarctica lipase B (CALB), Humicola insolens cutinase and Rhizomucor miehei lipase and were compared to results from computer simulations. More potent enzymes for acryltransfer, such as the CALB mutant V190A and acrylates with higher turnover numbers, showed elevated populations of productive transition states.     

Dimerization determines substrate specificity of a bacterial prenyltransferase

We have identified the native dimer interface of heptaprenylglyceryl phosphate synthase PcrB from the bacterium Bacillus subtilis and analyzed the significance of oligomer formation for stability and catalytic activity. Computational methods predicted two different surface regions of the PcrB protomer that could be responsible for dimer formation. These bona fide interfaces were assessed both in silico and experimentally by the introduction of amino acid substitutions that led to monomerization, and by incorporation of an unnatural amino acid to allow cross-linking of the two protomers. The results showed that, in contrast to previous assumptions, PcrB uses the same interface for dimerization as the homologous geranylgeranylglyceryl phosphate synthase from Archaea. Thermal unfolding demonstrated that the monomeric proteins are only slightly less stable than wild-type PcrB. However, activity assays showed that monomerization limits the length of accepted polyprenyl pyrophosphates to three isoprene units, whereas the native PcrB substrate contains seven isoprene entities. We provide a plausible hypothesis as to how dimerization determines substrate specificity of PcrB.     

Recent Progress in the Molecular Imaging of Nonalcoholic Fatty Liver Disease

Pathological fibrosis of the liver is a landmark feature in chronic liver diseases, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH). Diagnosis and assessment of progress or treatment efficacy today requires biopsy of the liver, which is a challenge in, e.g., longitudinal interventional studies. Molecular imaging techniques such as positron emission tomography (PET) have the potential to enable minimally invasive assessment of liver fibrosis. This review will summarize and discuss the current status of the development of innovative imaging markers for processes relevant for fibrogenesis in liver, e.g., certain immune cells, activated fibroblasts, and collagen depositions.