Tissue-specific pyruvate dehydrogenase complex deficiency causes cardiac hypertrophy and sudden death of weaned male mice

Pyruvate dehydrogenase complex (PDC) plays an important role in energy homeostasis in the heart by catalyzing the oxidative decarboxylation of pyruvate derived primarily from glucose and lactate. Because various pathophysiological states can markedly alter cardiac glucose metabolism and PDC has been shown to be altered in response to chronic ischemia, cardiac physiology of a mouse model with knockout of the alpha-subunit of the pyruvate dehydrogenase component of PDC in heart/skeletal muscle (H/SM-PDCKO) was investigated. H/SM-PDCKO mice did not show embryonic lethality and grew normally during the preweaning period. Heart and skeletal muscle of homozygous male mice had very low PDC activity (approximately 5% of wild-type), and PDC activity in these tissues from heterozygous females was approximately 50%. Male mice did not survive for >7 days after weaning on a rodent chow diet. However, they survived on a high-fat diet and developed left ventricular hypertrophy and reduced left ventricular systolic function compared with wild-type male mice. The changes in the heterozygote female mice were of lesser severity. The deficiency of PDC in H/SM-PDCKO male mice greatly compromises the ability of the heart to oxidize glucose for the generation of energy (and hence cardiac function) and results in cardiac pathological changes. This mouse model demonstrates the importance of glucose oxidation in cardiac energetics and function under basal conditions.     

Transesterification of primary and secondary alcohols using Pseudomonas aeruginosa lipase

Lipases of a newly isolated Pseduomonas aeruginosa MTCC 5113 were assessed for transesterification of benzyl alcohol and vinyl acetate to produce the flavoring agent benzyl acetate. Crude lipase preparations that minimized the cost of the biocatalyst, achieved benzyl alcohol conversion of 89% within 3h at 30 degrees C. In contrast, purified and expensive commercially available lipases of Candida antarctica and porcine pancreas achieved much lower conversions at 80% and 15%, respectively. A well-mixed ( approximately 800 rev.min(-1)) batch reactor having the aqueous phase finely dispersed in heptane was used in these studies. Benzyl alcohol conversion was maximal when the enzyme-containing aqueous phase constituted about 50% of the total reactor volume. Use of solvents such as hexane, benzene, toluene and dimethyl sulfoxide reduced conversion compared with the use of heptane.     

Probing the role of the chloride ion in the mechanism of human pancreatic alpha-amylase.

Human pancreatic alpha-amylase (HPA) is a member of the alpha-amylase family involved in the degradation of starch. Some members of this family, including HPA, require chloride for maximal activity. To determine the mechanism of chloride activation, a series of mutants (R195A, R195Q, N298S, R337A, and R337Q) were made in which residues in the chloride ion binding site were replaced. Mutations in this binding site were found to severely affect the ability of HPA to bind chloride ions with no binding detected for the R195 and R337 mutant enzymes. X-ray crystallographic analysis revealed that these mutations did not result in significant structural changes. However, the introduction of these mutations did alter the kinetic properties of the enzyme. Mutations to residue R195 resulted in a 20-450-fold decrease in the activity of the enzyme toward starch and shifted the pH optimum to a more basic pH. Interestingly, replacement of R337 with a nonbasic amino acid resulted in an alpha-amylase that no longer required chloride for catalysis and has a pH profile similar to that of wild-type HPA. In contrast, a mutation at residue N298 resulted in an enzyme that had much lower binding affinity for chloride but still required chloride for maximal activity. We propose that the chloride is required to increase the pK(a) of the acid/base catalyst, E233, which would otherwise be lower due to the presence of R337, a positively charged residue.     

Structural and functional characterization of a ubiquitin variant engineered for tight and specific binding to an alpha‐helical ubiquitin interacting motif

Ubiquitin interacting motifs (UIMs) are short α‐helices found in a number of eukaryotic proteins. UIMs interact weakly but specifically with ubiquitin conjugated to other proteins, and in so doing, mediate specific cellular signals. Here we used phage display to generate ubiquitin variants (UbVs) targeting the N‐terminal UIM of the yeast Vps27 protein. Selections yielded UbV.v27.1, which recognized the cognate UIM with high specificity relative to other yeast UIMs and bound with an affinity more than two orders of magnitude higher than that of ubiquitin. Structural and mutational studies of the UbV.v27.1‐UIM complex revealed the molecular details for the enhanced affinity and specificity of UbV.v27.1, and underscored the importance of changes at the binding interface as well as at positions that do not contact the UIM. Our study highlights the power of the phage display approach for selecting UbVs with unprecedented affinity and high selectivity for particular α‐helical UIM domains within proteomes, and it establishes a general approach for the development of inhibitors targeting interactions of this type.     

Development of a subunit vaccine for prevention of Clostridium difficile associated diseases: Biophysical characterization of toxoids A and B

Inactivation of bacterial toxins for use in human vaccines traditionally is achieved by treatment with formaldehyde. In contrast, the bivalent experimental vaccine for the prevention of C. difficile infections (CDI) that is currently being evaluated in clinical trials was produced using a different strategy. C. difficile toxins A and B were inactivated using site-directed mutagenesis and treatment with 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride/N-hydroxysulfosuccinimide (EDC/NHS). In the present work we investigate the effect of genetic and chemical modifications on the structure of inactivated toxins (toxoids) A and B. The far-UV circular dichroism (CD) spectra of wild type toxins, mutated toxins, and EDC/NHS-inactivated toxoids reveal that the secondary structure of all proteins is very similar. The near-UV CD spectra show that aromatic residues of all proteins are in a unique asymmetric environment, indicative of well-defined tertiary structure. These results along with the fluorescence emission maxima of 335 nm observed for all proteins suggest that the tertiary structure of toxoids A and B is preserved as well. Analytical ultracentrifugation data demonstrate that all proteins are predominantly monomeric with small fractions of higher molecular weight oligomeric species present in toxoids A and B. Differential scanning calorimetry data reveal that genetic mutations induce thermal destabilization of protein structures. Subsequent treatment with EDC/NHS results either in a minimal (1 °C) increase of apparent thermostability (toxoid B) or no change at all (toxoid A). Therefore, our two-step inactivation strategy is an effective approach for the preparation of non-toxic proteins maintaining native-like structure and conformation.     

Galectin-7 in the control of epidermal homeostasis after injury

Galectins, a family of β-galactoside binding lectins, have recently emerged as novel regulators of tissue homeostasis. Galectin-7 is predominantly expressed in stratified epithelia, especially in epidermis. We report here the generation of galectin-7–deficient mice that are viable and do not display phenotypical abnormalities in skin structure or expression of epidermal markers. However, these mice show unique defects in the maintenance of epidermal homeostasis in response to environmental challenges. First, after UVB irradiation in vivo, the apoptotic response is prematurely triggered and lasts longer in the mutant epidermis. This result contrasts with the proapoptotic role that had been proposed for galectin-7. Second, wound-healing experiments in vivo revealed that galectin-7–deficient mice displayed a reduced reepithelialization potential compared with wild-type littermates. This effect could be attributed to a defect in cell migration. Because galectin-7 is located in the podosomes of keratinocytes migrating out of skin explants in culture, we propose that this glycan-binding protein may directly influence cell/extracellular matrix interactions. Finally, we also detected an unexpected intense hyperproliferative reaction consecutive to both types of stress in galectin-7–deficient mice. Together, these studies provide the first genetic evidence showing that galectin-7 can modulate keratinocyte apoptosis, proliferation, and migration during skin repair.