title: Infection of cells expressing CXCR4 mutants lacking N-glycosylation at the N-terminal extracellular domain is enhanced for R5X4-dualtropic human immunodeficiency virus type-1.
abstract: BACKGROUND
  Infection with human immunodeficiency virus type-1 (HIV-1) requires binding of the viral envelope gp120 to CD4 and to the CXCR4 coreceptor. Both, gp120 and CXCR4 are subject to N-glycosylation. Here we investigated the influence of the N-linked glycans g1 and g2 present on CXCR4 for HIV-1 infection.
  
  
  METHODS
  The two CXCR4 N-glycosylation sites g1 (NYT) and g2 (NVS) were mutated by changing the first or third amino acids N or T/S to Q and A respectively (g1; N11Q or T13A; g2, N176Q or S178A). Human osteosarcoma cells (GHOST) expressing human CD4 and the various CXCR4 glycosylation mutants were tested for infection using NL4-3-based viruses with X4, R5 or R5X4-tropism differing only in the V3 loop region.
  
  
  RESULTS
  All constructed cell lines expressing the various CXCR4 glycomutants showed similar permissiveness for the X4-monotropic virus and no change in the coreceptor specificity that allows infection of a CCR5-dependent R5-monotropic virus. Interestingly, the removal of glycan g1 significantly enhanced the permissiveness of GHOST cells for the R5X4 dualtropic virus. GHOST cells expressing the CXCR4-g1 or CXCR4-g1/2 mutants were infected at higher rates by the R5X4-dualtropic virus compared to cells expressing CXCR4-wt or CXCR4-g2 coreceptors.
  
  
  CONCLUSIONS
  Our present observations underscore a role for glycans present on the CXCR4 coreceptor in the entry process of HIV-1. The data will help to better understand the multifaceted mechanism of HIV infection and the selective forces which drive HIV-1 evolution from mono- to dual-tropism.
authors.affiliation: Bernhard Nocht Institute for Tropical Medicine, Department of Virology, 20359 Hamburg, Germany. ithordsen@bni.uni-hamburg.de
authors.forename: Ingo
authors.initials: I
authors.lastname: Thordsen
authors.forename: Svenja
authors.initials: S
authors.lastname: Polzer
authors.forename: Michael
authors.initials: M
authors.lastname: Schreiber
mesh_terms: D006031:Glycosylation; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D009154:Mutation; D017434:Protein Structure, Tertiary; D019718:Receptors, CXCR4 / Q000235:genetics / Q000502:physiology*; D014162:Transfection; D018523:Tropism; D014407:Tumor Cells, Cultured / Q000821:virology
chemical_list: D019718:Receptors, CXCR4