Forms the virion spikes together with glycoprotein G2. The glycoprotein spike trimers are connected to the underlying matrix. Interacts with the host receptor. Mediates virus attachment to the host primary receptor alpha-dystroglycan DAG1 (alpha-DG) at the cell surface. This attachment induces virion internalization apparently through macropinocytosis. Following endocytosis, there is a pH-dependent switch from binding DAG1 to the host lysosomal receptor LAMP1. This latter binding triggers the dissociation of GP1, exposing the fusion subunit, GP2, such that fusion can occur. Down-modulates host DAG1