Dendritic cells (DC) was shown to enhance the efficiency of HIV-1 infection to T cells through the binding of viral gp120 to a DC surface C-type lectin-like receptor, DC-SIGN, and subsequent delivering of the viral particles to T cells. The recruitment of DC-SIGN by HIV to facilitate the viral infection makes the receptor a potential new target for vaccines and anti-viral therapy. We have expressed several soluble forms of DC-SIGN and DC-SIGNR using a bacterial system followed by in vitro reconstitution. The refolded CRD, R8 and Ecto forms of DC-SIGN exist in solution as monomer, dimer and tetramer, respectively, suggesting the function of the extracellular repeat region is to stabilize the oligomeric form of the receptor. All three forms of the soluble receptor bind to gp120 at near nM affinity. Antibodies were raised against the recombinant DC-SIGN(R8) and one (II.1) exhibits near complete inhibition to the receptor/ gp120 binding both in solution and on the surface of immature dendritic cells, whereas the other display variable inhibition effects. In addition to the anti-DC-SIGN antibodies, two anti-gp120 antisera were also tested but were not able to block the gp120 binding to DC-SIGN. All constructs of the soluble receptor were subjected to crystallization screening experiments and the preliminary results show small crystals of the receptor can be obtained.
