Using peptidyl aldehydes in activity-based proteomics

Naturally Inspired Peptide Leads: Alanine Scanning Reveals an Actin-Targeting Thiazole Analogue of Bisebromoamide

Systematic alanine scanning of the linear peptide bisebromoamide (BBA), isolated from a marine cyanobacterium, was enabled by solid-phase peptide synthesis of thiazole analogues. The analogues have comparable cytotoxicity (nanomolar) to that of BBA, and cellular morphology assays indicated that they target the actin cytoskeleton. Pathway inhibition in human colon tumour (HCT116) cells was explored by reverse phase protein array (RPPA) analysis, which showed a dose-dependent response in IRS-1 expression. Alanine scanning reveals a structural dependence to the cytotoxicity, actin targeting and pathway inhibition, and allows a new readily synthesised lead to be proposed.

Applications of copper-catalyzed click chemistry in activity-based protein profiling

Activity-based protein profiling (ABPP) is a chemical proteomic technique that enables the interrogation of protein activity directly within complex proteomes. Given the dominant role of posttranslational modifications in regulating protein function in vivo, ABPP provides a direct readout of activity that is not attained through traditional proteomic methods. ABPP relies on the design of covalent binding probes that either target a specific enzyme or a class of enzymes with related function. These covalent warheads are coupled to either fluorophores or biotin groups for visualization and enrichment of these active proteins. The advent of bioorthogonal chemistries, in particular, the copper (I)-catalyzed azide-alkyne cycloaddition (CuAAC), has benefitted the field of ABPP by achieving the following: (1) replacing bulky reporter groups with smaller alkyne or azide groups to promote cell permeability; (2) adding modularity to the system such that a single probe can be diversified with a variety of reporter groups without the need to develop new synthetic routes; and (3) enabling the conjugation of complex linkers to facilitate quantitative proteomic analyses. Here, we summarize recent examples of CuAAC in ABPP that serve to illustrate the contribution of bioorthogonal chemistry to advancing discoveries in this field.

Design and synthesis of anti-cancer cyclopeptides containing triazole skeleton

We describe the design and synthesis of some hypothetical heptapeptides specifically to overcome the neoplastic activity of ras oncogene and their anti-cancer activities were studied. To improve the anti-cancer activity of the synthesized peptides, their structure modifications were done based on a sequential Ugi/Huisgen 1,3-Dipolar cyclization reaction. The cyclopeptides which contained triazole skeleton showed significant anti-cancer activity against cancer cells with mutated ras oncogene such as A549, PC3 and C26 cells. This study clearly shows the importance of triazole skeleton in biological activity of the peptides. It might be possible to overcome the difficulties involved in making complex peptides by employing this elegant chemistry.

Sulfonyl fluoride analogues as activity-based probes for serine proteases

Enriched with fluoride: To expand on the available tools to interrogate proteases, we explored sulfonyl fluorides as activity-based probes. An alkyne-tagged sulfonyl fluoride covalently modifies members of the S1 family of serine proteases. By applying click chemistry, avidin enrichment and mass spectrometry, we can enrich and identify active endogenous serine proteases from a complex proteome.