Synthetic probes for bacterial lipids and dimerizing proteins

Abstract

This thesis includes two projects: “Bacteria-selective borono-peptides” and “A split ligand for lanthanide binding: facile evaluation of dimerizing proteins”. In both projects, de novo designed molecules were synthesized, optimized and incorporated into peptides. These synthetic molecular tools allow selective targeting of bacterial cell membranes and analyzing the dynamic associations of membrane-embedded proteins. 1. Bacteria-selective borono-peptides As the antibiotic resistance continues to grow, bacterial infection becomes one of the major threats to global public health. Currently, almost all the bacteria targeting strategies employ non-covalent driving forces, including charge-charge interactions, hydrophobic interactions and the formation of hydrogen bonds, to achieve bacterial selectivity. Towards novel bacteria targeting molecules, we have recruited reversible covalent chemistry in the development of bacteria-selective peptides. Targeting the diol-rich environment of a bacterial surface, we have designed and synthesized several unnatural amino acids that contain boronic acid moieties. Taking advantage of the boronic acid-diol reaction and multivalency effect, our borono-peptides are found to selectively recognize bacteria over mammalian cells. The sensitivity of the binding event to carbohydrate competitors gives a safe and facile approach to regulate molecular association with bacterial cells. This design may find applications in the fields of bacterial detection, imaging and antimicrobial drug delivery. 2. A split ligand for lanthanide binding: facile evaluation of dimerizing proteins Protein dimerization is a ubiquitous phenomenon in biology and plays a critical role in transcription regulations and various signaling processes. Methods that allow facile detection and quantification of protein dimers are highly desirable for evaluating protein dimerization in physiology and disease. Meanwhile, luminescence of lanthanides is attractive for biological applications due to its long lifetime and sharp emission profiles. We have developed a split lanthanide binding ligand that allows facile evaluation of dimerizing proteins. The fast lanthanide–ligand (dis)association allows us to monitor the dynamic behavior of dimerizing proteins. We have demonstrated the successful application of our assay on both soluble and transmembrane proteins in complex biological milieu. The split lanthanide ligand is cysteine reactive, and therefore should be readily applicable to a variety of proteins of interest.