Weichao Li

Profiling of Multiple Targets of Artemisinin Activated by Hemin in Cancer Cell Proteome

The antimalarial drug artemisinin is found to have diverse biological activities ranging from anti-inflammatory to anticancer properties; however, as of today, the cellular targets and mechanism of action of this important compound have remained elusive. Here, we report the global protein target profiling of artemisinin in the HeLa cancer cell proteome using a chemical proteomics approach. In the presence of hemin, multiple proteins were targeted by artemisinin probe through covalent modification. Further studies revealed that reducing of hemin to heme by protein thiols was essential for endoperoxide activation and subsequent protein alkylation. Artemisinin may exert its synergistic therapeutic anticancer effects via modulation of a variety of cellular pathways through acting on multiple targets.

Competitive profiling of celastrol targets in human cervical cancer HeLa cells via quantitative chemical proteomics

Celastrol, isolated from the traditional Chinese medicinal herb Tripterygium wilfordii Hook. f. (Thunder Gods Vine), has been used to treat cancer, chronic inflammatory, autoimmune and other human diseases. However, to date, the protein targets and the mechanism of action of celastrol have remained elusive. In this study, we find that celastrol can react with protein thiols in a unique covalent and reversible manner, while protein denaturing disrupts the interaction. Through a competitive chemoproteomics approach utilizing a cysteine-targeting activity-based probe, we report the proteome-wide quantitative profiling of cellular targets of celastrol in human cervical cancer HeLa cells. Representative targets are further validated via in vitro binding experiments and/or enzymatic activity assays. Bioinformatics analysis results suggest that celastrol exerts its numerous therapeutic effects through interaction with promiscuous proteins involved in various biological processes and cellular pathways.

Global profiling of cellular targets of gambogic acid by quantitative chemical proteomics

Gambogic acid has shown significant potential as an anti-cancer and anti-inflammatory compound; however, the molecular mechanism underlying the actions of gambogic acid, particularly its cellular target profiles, has not been investigated. In this study, we report the proteome-wide profiling of potential cellular targets of gambogic acid using quantitative mass spectrometry-based chemical proteomics. The target profiles of gambogic acid in living HeLa and K562 cells were identified, which strengthened our understanding of the mode of actions of the phytochemical.

Metabolism of ganoderic acids by a Ganoderma lucidum cytochrome P450 and the 3-keto sterol reductase ERG27 from yeast

Ganoderic acids, a group of oxygenated lanostane-type triterpenoids, are the major bioactive compounds produced by the well-known medicinal macro fungus Ganoderma lucidum. More than 150 ganoderic acids have been identified, and the genome of G. lucidum has been sequenced recently. However, the biosynthetic pathways of ganoderic acids have not yet been elucidated. Here, we report the functional characterization of a cytochrome P450 gene CYP512U6 from G. lucidum, which is involved in the ganoderic acid biosynthesis. CYP512U6 hydroxylates the ganoderic acids DM and TR at the C-23 position to produce hainanic acid A and ganoderic acid Jc, respectively. In addition, CYP512U6 can also hydroxylate a modified ganoderic acid DM in which the C-3 ketone has been reduced to hydroxyl by the sterol reductase ERG27 from Saccharomyces cerevisiae. An NADPH-dependent cytochrome P450 reductase from G. lucidum was also isolated and characterized. These results will help elucidate the biosynthetic pathways of ganoderic acids.

Deciphering the late steps of rifamycin biosynthesis.

Rifamycin-derived drugs, including rifampin, rifabutin, rifapentine, and rifaximin, have long been used as first-line therapies for the treatment of tuberculosis and other deadly infections. However, the late steps leading to the biosynthesis of the industrially important rifamycin SV and B remain largely unknown. Here, we characterize a network of reactions underlying the biosynthesis of rifamycin SV, S, L, O, and B. The two-subunit transketolase Rif15 and the cytochrome P450 enzyme Rif16 are found to mediate, respectively, a unique C–O bond formation in rifamycin L and an atypical P450 ester-to-ether transformation from rifamycin L to B. Both reactions showcase interesting chemistries for these two widespread and well-studied enzyme families.The enzymes Rif15 and Rif16 are involved in the late steps of the biosynthesis of rifamycins, a group of antibiotics. Here, the authors characterized these two proteins and found that they catalyse unusual biochemical reactions.

Chemoproteomics Reveals the Anti-proliferative Potential of Parkinson’s Disease Kinase Inhibitor LRRK2-IN-1 by Targeting PCNA Protein

LRRK2-IN-1, one of the first selective inhibitors of leucine-rich repeat kinase 2 (LRRK2), was serendipitously found to exhibit potent antiproliferative activity in several types of human cancer cells. In this study, we employed a chemoproteomic strategy utilizing a photoaffinity probe to identify the cellular target(s) of LRRK2-IN-1 underlying its anticancer activity. LRRK2-IN-1 was found to induce cell cycle arrest as well as cancer cell death by specifically binding to human proliferating cell nuclear antigen (PCNA) in cancer cells. Our current findings suggest the potential of LRRK2-IN-1 as a novel pharmacological molecule for scrutinizing cell physiology and furnish a logical foundation for the future development of therapeutic reagents for cancer.

Development of Photoaffinity Probe for the Discovery of Steviol Glycosides Biosynthesis Pathway in Stevia rebuadiana and Rapid Substrate Screening

Functional discovery and characterization of the target enzymes responsible for the biosynthesis pathway coded for the genes is ongoing, and the unknown functional diversity of this class of enzymes has been revealed by genome sequencing. Commonly, it is feasible in annotating of biosynthetic genes of prokaryotes due to the existence of gene clusters of secondary metabolites. However, in eukaryotes, the biosynthetic genes are not compactly clustered in the way of prokaryotes. Hence, it remains challenging to identify the biosynthetic pathways of newly discovered natural products in plants. Steviol glycosides are one class of natural sweeteners found in high abundance in the herb Stevia rebaudiana. Here, we applied the chemoproteomic strategy for the proteomic profiling of the biosynthetic enzymes of steviol glycosides in Stevia rebaudiana. We not only identified a steviol-catalyzing UDP-glycosyltransferase (UGT) UGT73E1 involved in steviol glycoside biosynthesis but also built up a probe-based platform for the screening of potential substrates of functional uncharacterized UGT rapidly. This approach would be a complementary tool in mining novel synthetic parts for assembling of synthetic biological systems for the biosynthesis of other complex natural products.