[Conserved W52 led to reduced binding of glucogan-like peptide 1 receptor]

Through phage display, we tried to find out whether the N-terminal fragment of glucogan-like peptide 1 receptor (nGLP-1R) still had binding activity to Exendin-4 after missing one or two gene segments. By error-prone PCR, We constructed a randomly mutated phage display peptide library with different length of the N-terminal (21-145 residues) extracellular domain of glucogan-like peptide 1 receptor (GLP-1R) from rat lung. A mutant named EP16 without binding activity was found by ELISA. Through sequence alignment we found that EP16 missed the first 20 and last 10 amino acids and the 52nd tryptophan was mutated to arginine. In order to determine why Ep16 did not show its binding ability to Exendin-4, a wild type EP16 without the first 20 and last 10 amino acids and nGLP-1R(W52R) was constructed in which the 52nd tryptophan was mutated to arginine. The contrastive analysis showed that the substitution of W52R led to a markedly reduced binding ability of EP16. The mutation of the conserved W52 could change the biologic activity of the protein. The lack of the first 20 and last 10 amino acids had no effect on its biologic activity. Therefore, the mutation of a single amino acid residue of the key sequence could change the biologic activity of the nGLP-1R.