The loss of a nucleotide pair is a frameshift mutation, which will totally change the encoded protein sequence and probably introduce a stop codon, truncating the protein. Protein functionality will almost certainly be lost.
Work Step by Step
Review the information on frameshift mutations and how destructive they are, especially if they are in the middle of a protein. It is as if someone in the middle of a page in your textbook moved the spacing so it fell in the middle of words instead of between them. You can imagine what nonsense the text would be then.