Article

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

Structural Molecular Microbiology, Vrije Universiteit Brussel, VIB, Brussels, Belgium.
Biochemistry (Impact Factor: 3.38). 06/2012; 51(24):4790-9. DOI: 10.1021/bi300251r
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
159 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent advances in small-angle X-ray scattering (SAXS) have led to the ability to model the glycans on glycoproteins and to obtain the low-resolution solution structures of complexes of lectins bound to multivalent glycan-presenting scaffolds. This progress in SAXS can respond to the increasing interest in the biological action of glycoproteins and lectins and in the design of multivalent glycan-based antagonists. Carbohydrates make up a significant part of the X-ray scattering content in SAXS and should be included in the model together with the protein, whose structure is most often based on a crystal structure or NMR ensemble, to give a far-improved fit with the experimental data. The modeling of the spatial positioning of glycans on proteins or in the architecture of lectin-glycan complexes delivers low-resolution structural information hitherto unmatched by any other method. SAXS data on the bacterial lectin FimH, strongly bound to heptyl α-D-mannose on a sevenfold derivatized β-cyclodextrin, permitted determination of the stoichiometry of the complex and the geometry of the lectin deposition on the multivalent β-cyclodextrin. The SAXS methods can be applied to larger complexes as the technique imposes no limit on the size of the macromolecular assembly in solution.
    Methods in molecular biology (Clifton, N.J.) 01/2014; 1200:511-26. · 1.29 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Intermolecular interactions involving carbohydrates and their natural receptors play important roles in several biological processes. The development of synthetic receptors is very useful to study these recognition processes. Recently, it was synthetized a diaminopyrrolic tripodal receptor that is selective for mannosides, which are obtained from mannose, a sugar with significant relevance in living systems. However, this receptor is significantly more active in acetonitrile than in water. In this work, we performed several molecular dynamics and constant-pH molecular dynamics simulations in acetonitrile and water to evaluate the conformational space of the receptor and to understand the molecular detail of the receptor-mannoside interaction. The protonation states sampled by the receptor show that the positive charges are always as distant as possible in order to avoid large intramolecular repulsions. Moreover, the conformational space of the receptor is very similar in water above pH 4.0 and in acetonitrile. From the simulations with the mannoside, we observe that the interactions are more specific in acetonitrile (mainly hydrogen bonds) than in water (mainly hydrophobic). Our results suggest that the readiness of the receptor to bind mannoside is not significantly affected in water (above pH 4.0). Probably, the hydrogen bond network that is formed in acetonitrile (which is weaker in water) is the main reason for the higher activity in this solvent. This work also presents a new implementation of the stochastic titration constant-pH molecular dynamics method to a synthetic receptor of sugars and attests its ability to describe the protonation/conformation coupling in these molecules.
    Beilstein Journal of Organic Chemistry 01/2014; 10:1513-1523. · 2.80 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Just like bacteria need to be mobile to seek for nutrients, bacteria need to adhere to biotic and abiotic surfaces to enable their progression. Most bacteria regulate the expression of a multitude of fimbrial adhesins that display varying specificities and architectures. FimH at the tip of type 1 fimbriae is one of the first recognized lectins on Escherichia coli. FimH evokes through its binding symptomatic and chronic E. coli infections in the urinary tract, in the intestine, and beyond. The mannose specificity of type 1 fimbriae has been the lead to the discovery of the FimH adhesin more than 32 years ago and presents today a role model as the template for anti-adhesive drug design. Curiously, the specificity of the FimH lectin had been defined very early on toward a Manα1,3Manβ1,4GlcNAc trisaccharide isolated from the urine of mannosidase-deficient patients. Indeed, a much larger dependence of bacterial adhesion can be attributed to structural differences in the mannosidic receptors than based on amino acid variance in FimH. The crystal structure of FimH in complex with oligomannoside-3 presented a breakthrough that enhanced the rational design of mannose-based anti-adhesives against FimH. In this overview, we will provide insights gained from a plethora of FimH antagonists. Crystal structures of FimH in complex with anti-adhesives and applications in vivo in mouse models for metabolic diseases reveal unexpected features and alternative routes for improved molecules.
    Top Med Chem, 2014 edited by Dr. Peter H. Seeberger, Dr. Christoph Rademacher, 08/2014: chapter 52; Springer-Verlag Berlin Heidelberg.

Full-text

Download
72 Downloads
Available from
Jun 3, 2014