Calcium-binding protein that interacts with rotavirus cell receptors once the initial attachment by VP4 has been achieved. Rotavirus attachment and entry into the host cell probably involves multiple sequential contacts between the outer capsid proteins VP4 and VP7, and the cell receptors. Following entry into the host cell, low intracellular or intravesicular Ca2+ concentration probably causes the calcium-stabilized VP7 trimers to dissociate from the virion. This step is probably necessary for the membrane-disrupting entry step and the release of VP4, which is locked onto the virion by VP7.