Abstract: The invention relates to a molecular peptide mutant, the amino acid sequence of which is as shown in SEQ ID NO: 1. In the invention, SpyCatcher is designed and modified to obtain a molecular peptide SpyCatcher-21 with stimulus response to pH on the basis of not affecting the formation of isopeptide bonds, and Pro is introduced into a key loop of the SpyCatcher-21 through analysis of the crystal structure to reduce the flexibility of the loop and obtain a mutant SpyCatcher-21_A82P, which can raise ligation efficiency with SpyTag. The SpyCatcher-21_A82P can be used to achieve double-enzyme catalysis according to objective needs by changing the pH of the environment to obtain different degrees of coupling, or obtain a three-enzyme coupled catalytic system through electrostatic interaction with a positively charged enzyme.