Hedgehog signaling is critical for correct embryogenesis and tissue development. However, on matu-
ration, signaling is also found to be aberrantly activated in many cancers. Palmitoylation of the secreted
signaling protein sonic hedgehog (Shh) by the enzyme hedgehog acyltransferase (Hhat) is required for
functional signaling. To quantify this important posttranslational modification, many in vitro Shh pal-
mitoylation assays employ radiolabeled fatty acids, which have limitations in terms of cost and safety.
Here we present a click chemistry armed enzyme-linked immunosorbent assay (clickeELISA) for
assessment of Hhat activity through acylation of biotinylated Shh peptide with an alkyne-tagged pal-
mitoyl-CoA (coenzyme A) analogue. Click chemistry functionalization of the alkyne tag with azido-FLAG
peptide allows analysis through an ELISA protocol and colorimetric readout. This assay format identified
the detergent n-dodecyl b - D -maltopyranoside as an improved solubilizing agent for Hhat activity.
Quantification of the potency of RU-SKI small molecule Hhat inhibitors by clickeELISA indicated IC 50
values in the low- or sub-micromolar range. A stopped assay format was also employed that allows
measurement of Hhat kinetic parameters where saturating substrate concentrations exceed the binding
capacity of the streptavidin-coated plate. Therefore, clickeELISA represents a nonradioactive method for
assessing protein palmitoylation in vitro that is readily expandable to other classes of protein lipidation.