Abstract
Burkholderia oklahomensis EO147 agglutinin (BOA) is a 29 kDa member of the Oscillatoria agardhii agglutinin (OAA) family of lectins. Members of the OAA family recognize high-mannose glycans, and, by binding to the HIV envelope glycoprotein 120 (gp120), block the virus from binding to and entering the host cell, thereby inhibiting infection. OAA-family lectins comprise either one or two homologous domains, with a single domain possessing two glycan binding sites. We solved the structure of BOA in the ligand-free form as well as in complex with four molecules of 3α,6α-mannopentaose, the core unit of the N-linked high-mannose structures found on gp120 in vivo. This is the first structure of a double-domain OAA-family lectin in which all four binding sites are occupied by ligand. The structural details of the BOA-glycan interactions presented here, together with determination of affinity constants and HIV inactivation data, shed further light onto the structure-function relationship in this important class of anti-HIV proteins.