Diyne inactivators and activity-based fluorescent labeling of phenol hydroxylase in Pseudomonas sp. CF600

An activity-based labeling (ABL) approach was investigated for the phenol-oxidizing bacterium, Pseudomonas sp. CF600. Phenol-grown cells were exposed to several different terminal diynes, and following cell breakage, extracts of these cells were added to copper-catalyzed alkyne/azide cycloaddition reactions containing Alexa Fluor 647 azide. Analysis of total cell proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and near-infrared scanning demonstrated covalent fluorescent labeling of a 58- and a 34-kDa polypeptide in all diyne-treated cell types. Further studies using 1,4-diethynylbenzene (DEB) demonstrated that these labeled polypeptides were consistently detected in cells grown on substrates that exhibited phenol-dependent O2 uptake activity but not observed when cells were grown on substrates such as dextrose or catechol that did not support this activity. Fluorescent labeling of the two polypeptides in DEB-treated, phenol-grown cells was time dependent and was inhibited by several known substrates for phenol hydroxylase. These results suggest that diverse diynes act as mechanism-based inactivators of phenol hydroxylase in Pseudomonas sp. CF600 and that this effect can be exploited by ABL approaches to selectively label the major 58- and 34-kDa subunits of the hydroxylase component of this complex enzyme.