How nature tunes isoenzyme activity in the multifunctional catalytic globin Dehaloperoxidase from Amphitrite ornata

Publication date: Available online 9 November 2017 Source:Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics Author(s): Leiah M. Carey, Roman Gavenko, Dimitri A. Svistunenko, Reza A. Ghiladi The coelomic hemoglobin of Amphitrite ornata, termed dehaloperoxidase (DHP), is the first known multifunctional catalytic globin to possess biologically-relevant peroxidase and peroxygenase activities. Although the two isoenzymes of DHP, A and B, differ in sequence by only 5 amino acids out of 137 residues, DHP B consistently exhibits a greater activity than isoenzyme A. To delineate the contributions of each amino acid substitution to the activity of either isoenzyme, the substitutions of the five amino acids were systematically investigated, individually and in combination, using 22 mutants. Biochemical assays and mechanistic studies demonstrated that the mutants that only contained the I9L substitution showed increased i) k cat values (peroxidase activity), ii) 5-Br-indole conversion and binding affinity (peroxygenase activity), and iii) rate of Compound ES formation (enzyme activation). Whereas the X-ray structures of the oxyferrous forms of DHP B (L9I) (1.96Å), DHP A (I9L) (1.20Å), and WT DHP B (1.81Å) showed no significant differences, UV–visible spectroscopy (ASoret/A380 ratio) revealed that the I9L substitution increased the 5-coordinate high-spin heme population characterized by the “open” conformation (i.e., distal histidine swung out of the pocket), wh...

Source: Biochimica et Biophysica Acta (BBA) Proteins and Proteomics - November 11, 2017 Category: Biochemistry Source Type: research