Explain why mutations that replace S/T/N residues with A/L/W residues in the N-terminal region of transmembrane proteins that function as cell surface receptors could significantly disrupt that utility of these proteins as receptors.

Serine (S), Threonine (T) and Asparagine (N) are primary binding sites of carbohydrates, and thereby they are required to form glycoproteins (i.e., glycosylation products)

Explanation:

A transmembrane protein (TP) is a particular type of protein that crosses the cell membrane in order to enable the movement of ions and molecules. Transmembrane proteins are divided into alpha-helical and beta-barrel proteins. The N-terminal region of transmembrane glycoproteins can be required for N-linked glycosylation, which is an enzymatic mechanism capable of attaching oligosaccharides to proteins in order to form glycoproteins (glycans). N-linked glycosylation is a posttranslational protein modification that has distinct functions depending on the cell type and the protein region involved in such modification. For example, in the surface of immune cells, the N-linked glycans are capable of dictating the migration pattern of these cells.