Human Behavior-Inspired Linchpin-Directed Catalysis for Traceless Precision Labeling of Lysine in Native Proteins.

The complex social ecosystem regulates the spectrum of human behavior. However, it becomes relatively easier to understand if we disintegrate the contributing factors, such as locality and interacting partners. Interestingly, it draws remarkable similarity with the behavior of a residue placed in a social setup of functional groups in a protein. Can it inspire principles for creating a unique environment for the precision engineering of proteins? We demonstrate that localization-regulated interacting partner(s) could render precise and traceless single-site modification of structurally diverse native proteins. The method targets a combination of high-frequency Lys residues through an array of reversible and irreversible reactions. However, excellent simultaneous control over chemoselectivity, site selectivity, and modularity ensures that the user-friendly protocol renders acyl group installation, including post-translational modifications (PTMs), on a single Lys. Besides, it offers a chemically orthogonal handle for the installation of probes. Also, a purification protocol integration delivers analytically pure single-site tagged protein bioconjugates. The precise labeling of a surface Lys residue ensures that the structure and enzymatic activities remain conserved post-bioconjugation. For example, the precise modification of insulin does not affect its uptake and downstream signaling pathway. Further, the method enables the synthesis of homogeneous antibody-fluorophore and antibody-drug conjugates (AFC and ADC; K183 and K249 labeling). The trastuzumab-rhodamine B conjugate displays excellent serum stability along with antigen-specific cellular imaging. Further, the trastuzumab-emtansine conjugate offers highly specific antiproliferative activity toward HER-2 positive SKBR-3 breast cancer cells. This work validates that disintegrate theory can create a comprehensive platform to enrich the chemical toolbox to meet the technological demands at the chemistry, biology, and medicine interface.

Linchpin-directed precise labeling of lysine in native proteins, purification, and analysis.

The proteins are critical building blocks of living systems and serve as a tool for their investigation and intervention. Their precision engineering enables its tuning and expands the functional landscape. Among various proteinogenic amino acids, high-frequency lysine offers a promising bioconjugation target. However, it is also among the most challenging candidates for homogeneous single-site modification. The linchpin-directed modification (LDM) addresses this concern by offering chemoselective, site-selective, and modular protein bioconjugation. The protocol outlines a general method for single-site modification of a native protein. At first, the selected LDM reagent constructs a stable bioconjugate through acylation of the Lys side chain. Subsequently, its chemically orthogonal handle creates an opportunity to install desired probes directly. Alternatively, the same group enables bioconjugate enrichment through ordered immobilization. The subsequent release, coupled with probe installation, renders analytically pure single-site tagged protein bioconjugate. The analysis of these constructs involves intact MS of protein bioconjugate, peptide mapping, and MS-MS for the site of modification and homogeneity.