The expression and purification of the A 2A -StaR2-b RIL 562 construct was carried out following the protocol described previously . The receptor was expressed using the Bac-to-Bac Expression System (Invitrogen) in Trichoplusa ni Tni PRO cells using ESF 921 medium (Expression Systems) supplemented with 5% (v/v) fetal bovine serum (Sigma-Aldrich) and 1% (v/v) Penicillin/Streptomycin (PAA Laboratories). Cells were infected at a density of 2.6 × 106 cells/ml with virus at an approximate multiplicity of infection of 1 and grown for 48 hours at 27 °C with constant shaking.