The mannose receptor mediates dengue virus infection of macrophages.

Macrophages (MØ) and mononuclear phagocytes are major targets of infection by dengue virus (DV), a mosquito-borne flavivirus that can cause haemorrhagic fever in humans. To our knowledge, we show for the first time that the MØ mannose receptor (MR) binds to all four serotypes of DV and specifically to the envelope glycoprotein. Glycan analysis, ELISA, and blot overlay assays demonstrate that MR binds via its carbohydrate recognition domains to mosquito and human cell-produced DV antigen. This binding is abrogated by deglycosylation of the DV envelope glycoprotein. Surface expression of recombinant MR on NIH3T3 cells confers DV binding. Furthermore, DV infection of primary human MØ can be blocked by anti-MR antibodies. MR is a prototypic marker of alternatively activated MØ, and pre-treatment of human monocytes or MØ with type 2 cytokines (IL-4 or IL-13) enhances their susceptibility to productive DV infection. Our findings indicate a new functional role for the MR in DV infection.

Characterization of a family 54 alpha-L-arabinofuranosidase from Aureobasidium pullulans.

A glycosyl hydrolase family 54 (GH54) alpha-L-arabinofuranosidase gene (abfA) of Aureobasidium pullulans was amplified by polymerase chain reaction from genomic DNA and a 498-amino-acid open reading frame deduced from the DNA sequence. Modeling of the highly conserved A. pullulans AbfA protein sequence on the crystal structure of Aspergillus kawachii AkabfB showed that the catalytic amino acid arrangement and overall structure were highly similar including the N-terminal catalytic and C-terminal arabinose binding domains. The abfA gene was expressed in Saccharomyces cerevisiae, and the heterologous enzyme was purified. The protein was monomeric, migrating at 49 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and eluting at 36 kDa upon gel filtration. AbfA showed maximal activity at 55 degrees C and between pH 3.5 and pH 4. The enzyme had a K (m) value for p-nitrophenyl-alpha-L-arabinofuranoside of 3.7 mM and a V (max) of 34.8 micromol min(-1) mg protein(-1). Arabinose acted as a noncompetitive inhibitor with a K (i) of 38.4 mM. The enzyme released arabinose from maize fiber, oat spelt arabinoxylan, and wheat arabinoxylan, but not from larch wood arabinogalactan or alpha-1,5-debranched arabinan. AbfA displayed low activity against alpha-1,5-L-arabino-oligosaccharides. The enzyme acted synergistically with endo-beta-1,4-xylanase in the breakdown of wheat arabinoxylan. Binding of AbfA to xylan from several sources confirmed the presence of a functional carbohydrate-binding module.