Structural determination of the K14 capsular polysaccharide from an ST25 Acinetobacter baumannii isolate, D46

The structure of the capsular polysaccharide (CPS) recovered from D46, an extensively antibiotic resistant ST25 Acinetobacter baumannii clinical isolate, was elucidated. The structure was resolved on the basis of NMR spectroscopy and chemical analyses, and was found to contain a branched neutral pentasaccharide with a backbone composed of GalpNAc and Galp residues, all d configured, and a d-Glcp side group. The KL14 gene cluster found in the D46 genome includes genes for four glycosyltransferases but no modules for synthesis of complex sugars, and this is consistent with the structure of K14. The K14 structure and KL14 sequence clarify the relationship between the structure and K locus sequence for A. nosocomialis isolate LUH5541. The identity of the first sugar of the K14 repeat unit (K unit), and the functions of the four encoded glycosyltransferases and Wzy polymerase were predicted.

Structure of the K6 capsular polysaccharide from Acinetobacter baumannii isolate RBH4

The structure of the capsular polysaccharide (CPS) from an Acinetobacter baumannii global clone 2 (GC2) clinical isolate RBH4 that carries the KL6 gene cluster was elucidated by means of chemical and spectroscopical methods. The repeating unit of K6 CPS is linear and contains N-acetyl-d-galactosamine (d-GalpNAc), two d-galactose (d-Galp) residues and 5,7-di-N-acetylpseudaminic acid (Pse5Ac7Ac). The synthesis of these sugars could be attributed to genes in the KL6 capsule biosynthesis gene cluster, and the formation of the linkages between the sugars were assigned to glycosyltransferases or the Wzy polymerase encoded in KL6.

A phosphorylation-induced turn defines the Alzheimer's disease AT8 antibody epitope on the tau protein

Post mortem biochemical staging of Alzheimer’s disease is currently based on immunochemical analysis of brain slices with the AT8 antibody. The epitope of AT8 is described around the pSer202/pThr205 region of the hyperphosphorylated form of the neuronal protein tau. In this study, NMR spectroscopy was used to precisely map the AT8 epitope on phosphorylated tau, and derive its defining structural features by a combination of NMR analyses and molecular dynamics. A particular turn conformation is stabilized by a hydrogen bond of the phosphorylated Thr205 residue to the amide proton of Gly207, and is further stabilized by the two Arg residues opposing the pSer202/pThr205.

Synthesis of 19F nucleic acid–polymer conjugates as real-time MRI probes of biorecognition

Polymer-DNA conjugates in which one nucleic acid strand contains fluorine-substituted nucleobases have been prepared and characterised. The efficacy of these novel F-19 nucleic acid-polymer conjugates as sensitive and selective in vitro reporters of DNA binding events is demonstrated through a number of rapid-acquisition MR sequences. The conjugates respond readily and in a sequence specific manner to external target oligonucleotide sequences by changes in hybridisation. In turn, these structural changes in polymer-nucleotide conjugates translate into responses which are detectable in fluorine relaxation and diffusion switches, and which can be monitored by in vitro Spin Echo and DOSY NMR spectroscopy. Although complementary to conventional FRET methods, the excellent diagnostic properties of fluorine nuclei make this approach a versatile and sensitive probe of molecular structure and conformation in polymeric assemblies.