Part of an ABC transporter complex involved in the uptake of guanosine (PubMed:21926227). Is probably the substrate-binding protein of the system (PubMed:21926227). May be a nucleoside transporter of broad specificity but with various affinities for different substrates (PubMed:21926227). The complex is composed of two ATP-binding proteins (NupO), two transmembrane proteins (NupP and NupQ) and a solute-binding protein (NupN). Present in detergent-resistant membrane (DRM) fractions that may be equivalent to eukaryotic membrane rafts; these rafts include proteins involved in signaling, molecule trafficking and protein secretion. Transcriptionally regulated by CodY. A null mutation does not lead to any detectable defect in guanosine uptake. However, in the nupG-nupN double mutant, guanosine uptake is reduced to an almost undetectable level. Belongs to the BMP lipoprotein family. Truncated N-terminus.