A channel protein specific for calcium ions was found to have a pore lined with six glutamate residues that participate in coordinating the calcium ion. What would happen to the selectivity of the pore if the Glu residues were mutated to Asp residues

If the mutation takes place, then the shorter side chains of asp compare to Glu will affect the permeability of the transport protein to calcium ions. Specifically, the mutation will increase the sizes of the pore, which in turn decreases the selectivity for calcium ion. Hence this affect excitability of the cell.