Responsible for binding to the receptor(s) on target cells. Interacts with CD209/DC-SIGN and CLEC4M/DC-SIGNR which act as cofactors for virus entry into dendritic cells (DCs) and endothelial cells. Binding to the macrophage specific lectin CLEC10A also seems to enhance virus infectivity. Interaction with FOLR1/folate receptor alpha may be a cofactor for virus entry in some cell types, although results are contradictory. Members of the Tyro3 receptor tyrosine kinase family also seem to be cell entry factors in filovirus infection. Once attached, the virions are internalized through clathrin-dependent endocytosis and/or macropinocytosis. After internalization of the virus into the endosomes of the host cell, proteolysis of GP1 by two cysteine proteases, CTSB/cathepsin B and CTSL/cathepsin L removes the glycan cap and allows GP1 binding to the host entry receptor NPC1. NPC1-binding, Ca(2+) and acidic pH induce a conformational change of GP2, which unmasks its fusion peptide and permit membranes fusion