The tyrosine gate as a potential entropic lever in the receptor-binding site of the bacterial adhesin FimH.

Uropathogenic Escherichia coli (UPEC) are the major causative agents of urinary tract infections. During infection, UPEC adhere to mannosylated glycoreceptors on the urothelium via the FimH adhesin located at the tip of type 1 pili. Synthetic FimH antiadhesives such as alkyl and phenyl α-D-mannopyranosides are thus ideal candidates for the chemical interception of this crucial step in pathogenesis. The crystal structures of the FimH lectin domain in its ligand-free form and in complexes with eight medium- and high-affinity mannopyranoside inhibitors are presented. The thermodynamic profiles of the FimH-inhibitor interactions indicate that the binding of FimH to α-D-mannopyranose is enthalpy-driven and has a negative entropic change. Addition of a hydrophobic aglycon influences the binding enthalpy and can induce a favorable entropic change. The alleviation of the entropic cost is at least in part explained by increased dynamics in the tyrosine gate (Tyr48 and Tyr137) of the FimH receptor-binding site upon binding of the ligand. Ligands with a phenyl group directly linked to the anomeric oxygen of α-D-mannose introduce the largest dynamics into the Tyr48 side chain, because conjugation with the anomeric oxygen of α-D-mannose forces the aromatic aglycon into a conformation that comes into close contact (≈2.65 Å) with Tyr48. A propargyl group in this position predetermines the orientation of the aglycon and significantly decreases affinity. FimH has the highest affinity for α-D-mannopyranosides substituted with hydrophobic aglycons that are compatible in shape and electrostatic properties to the tyrosine gate, such as heptyl α-D-mannose.

Coronary artery fixation at iso-arterial pressure: impacts on histologic evaluation and clinical management.

Coronary angiography is the standard imaging method for determining the site, extent, and severity of coronary artery disease. Several publications have reported discordance between the degree of coronary artery stenosis determined from post-mortem histologic evaluation and coronary angiography. While the 2-dimensional limitations of coronary angiography are well established, the determination of coronary stenosis based on histologic evaluation of passively fixed samples is also associated with significant biases. In this study, we used patients with chronic coronary artery disease to compare the stenosis severity estimates that were determined using the passive fixation method with those determined using the active fixation method. Our results showed a significant discrepancy between the stenosis in passively fixed coronary arteries when compared with coronary angiography in all major coronary vessels combined (P=.002), and in Cx (P=.045) and CD (P=.026). However, there was no mean difference when compared with perfused (actively fixed) samples when all vessels were combined or examined individually. Iso-physiologic mechanical perfusion (active) fixation yielded significantly reduced coronary artery stenosis means when compared to the passive fixation method in post-mortem evaluations during autopsies. This was evident when all vessels were combined (P=.0001) and assessed individually (Cx (P=.003), LAD (P=.025), LM (P=.056) and RC (P=.007)). Autopsies including cardiac explant patients also showed differences in estimates for all vessels combined (P=.0001) and in Cx (P=.016) and RC (P=.006). In summary, our quantitative histopathology analyses using perfused coronary artery stenosis at physiologic pressure showed significant discrepancies when compared with passive histopathology.

Tri- and hexavalent mannoside clusters as potential inhibitors of type 1 fimbriated bacteria using pentaerythritol and triazole linkages.

Several oligomannoside clusters having a hundred-fold increase in affinities toward E. coli were synthesized by Cu(I)-catalyzed [1,3]-dipolar cycloadditions using pentaerythritol scaffolds bearing either alkyne or azide functionalities.

Divergent Expression and Metabolic Functions of Human Glucuronosyltransferases through Alternative Splicing.

Maintenance of cellular homeostasis and xenobiotic detoxification is mediated by 19 human UDP-glucuronosyltransferase enzymes (UGTs) encoded by ten genes that comprise the glucuronidation pathway. Deep RNA sequencing of major metabolic organs exposes a substantial expansion of the UGT transcriptome by alternative splicing, with variants representing 20% to 60% of canonical transcript expression. Nearly a fifth of expressed variants comprise in-frame sequences that may create distinct structural and functional features. Follow-up cell-based assays reveal biological functions for these alternative UGT proteins. Some isoforms were found to inhibit or induce inactivation of drugs and steroids in addition to perturbing global cell metabolism (energy, amino acids, nucleotides), cell adhesion, and proliferation. This work highlights the biological relevance of alternative UGT expression, which we propose increases protein diversity through the evolution of metabolic regulators from specific enzymes.