Residues D155, P160, and K211 of MACV GPC had an intermediate effect on hTfR1 binding and cell-entry, with the first two amino acids being more predominant. These residues were not found to contact hTfR1 residues in the crystal structure and could exert their effect on cell-surface binding and entry by affecting overall or local folding of MACV GP1 and possibly by interacting with a yet unknown attachment or entry factor. P160 is conserved among all Clade B New World arenaviruses (Fig. 1, top  panel) , which use TfR1 as a receptor [1, 21] . However, D155 is conserved only among Clade B New World arenaviruses that cause hemorrhagic fevers in humans and bind hTfR1. Amapari (AMAV) and Tacaribe (TCRV) viruses, which are considered non-pathogenic for humans [2] and which do not bind hTfR1 but bind TfR1 of their mammalian hosts [21] , do not have an aspartate residue in this position (Fig. 1, top panel) .