Kinetic Studies on Proteolysis by Co(III) Complex of Cyclen

Abstract

As a new paradigm for drug design, we have proposed catalytic drugs based on target-selective peptide-cleaving catalysts. [1][2][3][4][5][6][7][8][9] In the conventional approaches to design drugs that regulate the activities of disease-related proteins such as enzymes, receptors, or ion channels, attempts are made to discover small molecules that bind to the active sites of the disease-related proteins with high selectivity and high affinity. One molecule of the conventional drug can control the activity of at most one molecule of the target protein.When the substrate of a target-selective artificial protease is a protein related to a disease, the artificial protease can cleave and inactivate the target protein acting as a catalytic drug.Peptide-cleaving catalytic drugs have several advantages in comparison with conventional drugs. First, the catalytic nature of peptide cleavage allows decreases in the amounts of the drug dose and the reduction of the side effects. Second, strong binding to the target is not required if the peptide cleavage is fast enough for the peptide-cleaving catalysts. Third, the peptide-cleaving catalysts can be obtained even for proteins or peptides lacking active sites.We have discovered the first target-selective artificial protease by cleaving the backbone of myoglobin by hydrolysis.3,4 In addition, we were able to design an artificial protease that selectively hydrolyzed the polypeptide backbone of peptide deformylase, 5 a bacterial enzyme regarded as an important target 10 for designing antibiotics. We also synthesized artificial proteases selective for oligomers of amyloid β-42 peptide, 9 the pathogenic species 11 for Alzheimer's disease. Moreover, we have reported catalysts for oxidative decarboxylation of N-terminal aspartate residues of oligopeptides such as angiotensin II 6 and melanin-concentration hormone, 7,8 which are targets for designing drugs for hypertension 12 and obesity, 13 respectively. As the catalytic center for the peptide-cleaving catalysts, we have exploited the Co(III) complex of cyclen (Co(III)-cyclen). Co(III)cyclen itself has some activity for hydrolytic cleavage of peptide bonds. The catalytic activity of Co(III)-cyclen is enhanced to a high level by connecting it to a binding site which recognizes the target protein or peptide. If the effective concentration of Co(III)cyclen toward a reaction site on the target is sufficiently high in the targetcatalyst complex, peptide cleavage occurs at a reasonably high rate.If the Co(III)cyclen moiety of a peptide-cleaving catalyst cleaves non-target proteins in vivo, the catalyst can cause serious side effects. To utilize peptide-cleaving catalysts as catalytic drugs, therefore, it is necessary to demonstrate that random attack of the catalysts at non-target proteins is negligible.The kinetic data for the hydrolysis of an amide (formylmorpholine) by Co(III)cyclen have been reported.14 The second-order rate constant for the reaction was estimated as 0.26 M −1 h −1 at 60 o C and pD 5.9. Unlike the amide molecule, prote...

Peptide Hydrolysis by Metal (Oxa)cyclen Complexes: Revisiting the Mechanism and Assessing Ligand Effects

“…Upon going from the cobalt 1 complex to the copper 1 Cu complex, we computed an appreciable reduction of the overall free-energy barrier of 3.5 kcal mol −1 , indicating that Cu(II) is more reactive than Co(III) metal. This trend is clearly observed when the experimental rate constants of the cobalt(III) and copper(II) cyclen complexes are compared, 10,15,16 for which the estimated energy difference is ∼2 kcal mol −1 (Table S2). For oxacyclen complexes, the energy difference is smaller (Table S2), 10,13,17,19 but a comparison between them is more difficult because Co and Cu complexes could be active in different structural isomers.…”

“…Specifically, Co­(III)- and Cu­(II)-based complexes with tetradentate 1,4,7,10-tetraazacyclododecane (cyclen) or 1-oxa-4,7,10-triazacyclododecane (oxacyclen) ligands have shown the ability to hydrolyze selectively a wide range of biological molecules such as lysozyme, myoglobin, albumin, globulin, amyloid-β (Aβ) peptide, or human islet amyloid peptide (h-IAPP). − Importantly, the cyclen family of ligands can incorporate an organic alkyl or aryl pendant that induces an enzyme-like recognition of the catalyst by the biological system, in such a way that the hydrolysis process becomes highly selective. This approach has been successfully applied to hydrolyze Aβ oligopeptides selectively at peptide bonds of Phe20–Ala21 and Ala21–Glu22, , making metal cyclen complexes highly attractive as a novel family of drugs for Alzheimer’s disease, which is presumably caused by the formation of misfolded aggregates of Aβ oligomers .…”

Distinct chemical factors in hydrolytic reactions catalyzed by metalloenzymes and metal complexes

“…The barrier of 30.5 kcal mol −1 for the Co-I C complex without the pendent is in agreement with the measured barrier of 25.9 kcal mol −1 for the hydrolysis of myoglobin at pH 9.0 and 50 °C. 170 Additionally, barriers of 39.8 kcal mol −1 for Co-I C and 40.1 kcal mol −1 for its oxacyclen derivative Co-I OC for the same mechanism are supported by the measured data that their activities differ by only four times. 164 Furthermore, Ni (in the triplet state) is the most feasible substitution among Ni( ii ), Zn( ii ), Cd( ii ), and Pd( ii ) complexes without the pendent and hydrolyzes the peptide bond with the lowest barrier of 27.2 kcal mol −1 .…”