In this study, we propose a reversible covalent conjugation method for peptides, proteins, and even live cells based on specific recognition between natural amino acid sequences. Two heptad sequences can specifically recognize each other and induce the formation of a disulfide bond between cysteine residues. We show the covalent bond formation and dissociation between peptides and proteins in cell-free conditions and on the surface of live cells. Because heptad sequences consist of natural amino acids, they are expressed in cells without additional preparation and can be used to selectively conjugate peptides, proteins, and cells.