Thursday, December 30, 2010

Enzyme-linked click chemistry assay for GOAT

cat-ELCCA, enzyme-linked click chemistry assay, was developed by Janda Group for high througput assay of GOAT, Ghrelin O-Acetyl transferase. The methodology is depicted in the drawing. The following chemistries are elegantly combined for the assay: biotin-straptavidin binding, CuAAC click chemistry, HRP catalysis, O-acetyltransferase catalysis, and fluorogenic reaction.

The method should accelerate identification of inhibitors for GOAT, which activates ghrelin by esterification with a C-8 fatty acid unit. It intimately relates to the effort of seeking agents that lower ghrelin levels as obesity or diabetes treatments.

Much like the cat-ELISA assays in immunology, cat-ELCCA, should find applications in other acyltransferases.

Angew. Chem. Int. Ed. 2010, 9630.

Monday, December 27, 2010

Click chemistry meets Cysteine

Ah Cysteine!

How many things happen with it: enzyme activity function, posttranslational modification, crosslinking, redox chemistry, Glutathione, GST the phase II detoxiciation, oxidative stress relief, etc. Everything happens around this unique one amino acid due to its R-SH reactivity.

Benjamin Cravatt and his group at Scripps Research Institute reported a click chemistry approach to obtain a proteome-wide quantitative analysis of native cysteine reactivity, in particular, the identification of hyper-reactive cysteine sites.

The appraoch is termed isoTOP-ABPP (isotopic tandem orthogonal proteolysis–activity-based protein profiling) and shown in the graph. The identified hyper-reactive cysteines correspond well to those of functional and posttranslational modification sites.

Benjamin Cravatt is well known for ABPP and I listened to his talk in Atlanta, 2006. He is one of the pioneers applying click chemistry to chemical biology research. See JACS 2003, 4686. "Activity-Based Protein Profiling in Vivo Using a Copper(I)-Catalyzed Azide-Alkyne [3 + 2] Cycloaddition"

Wonderful walking in the cold air on a Holiday morning - as well as surveying click chemistry progresses with a cup of hot coffee!

Friday, December 24, 2010

Labeling of live cells via Copper-catalyzed click chemistry

Copper-free click chemistry developed by Bertozzi Group allowed in vivo labeling and imaging of glycans without copper toxicity. This was reported widely by many media and scientific magazines. A summary on this topic will be given elsewhere.
Now two reports appeared using Copper-catalyzed click chemistry for the same purpose. The key is the identification of good ligands for Copper (1+) ion which allow for rapid labeling and minimal toxicity.
Vu Hong, M. G. Finn et al, "Labeling Live Cells by Copper-Catalyzed Alkyne-Azide Click Chemistry", Bioconj. Chem. received 6/17/2010.
Rapidly labels mammalian cells in culture with no loss in cell viability. Metabolic uptake and display of the azide derivative of N-acetylmannosamine (Bertozzi) followed by CuAAC reaction with dye-alkyne  

David Soriano del Amo, Peng Wu et al, "Biocompatible Copper(I) Catalysts for in Vivo Imaging of Glycans", JACS received 7/23/2010.
Rapid labeling and imaging of fucosylated glycans during zebrafish early embryogenesis without apparent toxicity. Alkyne-bearing  GDP-fucose microinjected and CuAAC reaction with dye-azide.