Finally, it is difficult to establish the role of MACV GPC residues N178 and D159 in cell binding and entry of the virus. In the context of purified GP1D, mutation of these amino acids did not affect overall folding (Fig. 2D) , but in the context of GPC these mutants failed to be incorporated into MoMLV pseudotypes. These results suggest that mutagenesis of N178 and D159 might lead to small changes in folding of GP1 (not being detected by CD) that might affect accessibility of hTfR1-binding residues in their vicinity. Alternatively, trafficking, folding, or binding of GP1 to SSP or GP2 might be defective only in the context of full-length GPC. The MACV GP1-hTfR1 crystal structure revealed seven Nlinked glycans on Asn178 [25] . It is plausible that these glycans play an important role in MACV glycoprotein folding, trafficking, GP complex formation, or entry. N178 and D159 (with the exception of CHPV) are conserved among all Clade B New World arenaviruses (Fig. 1, top panel) , which use TfR1 as a receptor [1, 21] .