Isocyanide binding to the copper(I) centers of the catalytic core of peptidylglycine monooxygenase (PHMcc)

Binding of the Cu(I)-specific ligands 2,6-dimethylphenyl isocyanide (DIMPI) and isopropyl isocyanide (IPI) to the reduced form of peptidylglycine mono oxygenase (PHM) is reported. Both ligands bind to the methionine-containing Cu-M center, eliciting FTIR bands at 2138 and 2174 cm(-1), respectively, b ut appear unable to coordinate at the histidine-containing CUH center in th e wild-type enzyme. This chemistry parallels that previously observed for C O binding to the reduced PHM catalytic core (PHMcc). However, in contrast t o the CO chemistry, peptide substrate binding did not induce binding of the isocyanide at Cu,. XAS confirmed the binding of DIMPI at CUM via the obser vation of a short Cu-C interaction at 1.87 Angstrom and by the lengthening of the Cu-S(methionine) bond length by 0.06 Angstrom. Similarly, FTIR studi es on DIMPI binding to the M314I and H172A mutant forms of reduced PHMcc co nfirmed the assignment of the 2138-cm(-1) IR band as a Cu-M-DIMPI complex, but surprisingly also showed DIMPI binding to Cu-H as indicated by a band a t 2148 cm(-1). An inorganic complex, [Cu(1,2-Me(2)Im)(2)(DIMPI)] (PF6), was synthesized and its crystal structure was determined as a model for the in teraction of isocyanides with imidazole-containing Cu(I) complexes. Compari son of EXAFS data for the protein and model suggests that DIMPI probably bi nds to Cu, in a tilted fashion, similar to that of ethyl isocyanide binding to myoglobin.