Cobalt tetradehydrocorrins coordinated by imidazolate-like histidine in the heme pocket of horseradish peroxidase

Abstract

Horseradish peroxidase was reconstituted with cobalt tetradehydrocorrin, rHRP(Co(TDHC)), as a structural analog of cobalamin coordinated with an imidazolate-like His residue, which is generally seen in native enzymes. In contrast to the previously reported cobalt tetradehydrocorrin-reconstituted myoglobin, rMb(Co(TDHC)), the HRP matrix was expected to provide strong axial ligation by His170 which has imidazolate character. rHRP(Co(TDHC)) was characterized by EPR and its reaction with reductants indicates a negative shift of its redox potential compared to rMb(Co(TDHC)). Furthermore, aqua- and CN-forms of Co(III) state were prepared. The former species was obtained by oxidation of rHRP(Co(TDHC)) with K[Fe(CN)]. The cyanide-coordinated Co(III) species in the latter was prepared by ligand exchange of rHRP(Co(OH)(TDHC)) with exogenous cyanide upon addition of KCN. The C NMR chemical shift of cyanide in rHRP(Co(CN)(TDHC)) was determined to be 121.8 ppm. IR measurements show that the cyanide of rHRP(Co(CN)(TDHC)) has a stretching frequency peak at 2144 cm. The C NMR and IR measurements indicate strong coordination of cyanide to Co(TDHC) relative to rMb(Co(CN)(TDHC)). Thus, the extent of π-back donation from the cobalt ion to the cyanide ion is relatively high in rHRP(Co(CN)(TDHC)). The pK values of rHRP(Co(OH)(TDHC)) and rHRP(Co(CN)(TDHC)) are the same (pK = 3.2) as determined by a pH titration experiment, indicating that cyanide ligation does not affect Co-His ligation, whereas cyanide ligation weakens the Co-His ligation in rMb(Co(CN)(TDHC)). Taken together, these results indicate that HRP reconstituted with cobalt tetradehydrocorrin is a suitable cobalamin-dependent enzyme model with imidazolate-like His residue.

Hemoproteins Reconstituted with Artificial Metal Complexes as Biohybrid Catalysts

“…The large size of the enzyme causes challenges in elucidation of its reaction mechanisms . In this context, a cobalt tetradehydrocorrin derivative 8 was designed as a model of cobalamin, and rMb­( 8 ) was prepared and investigated as a hybrid model to replicate the reaction promoted by methionine synthase. − The Co­(II) species of rMb­( 8 ) was first prepared, and its crystal structure revealed ligation of His93 to the Co center in the heme pocket (Figure ). Soaking the Co­(II) crystals in a dithionite solution successfully provided the crystals to the Co­(I) species.…”

Supramolecular Control over Split‐Luciferase Complementation

“…[1,2] Supramolecular systems have become increasingly complex, creating new opportunities for interfacing with biology. [3][4][5] As evidence of this,s upramolecular architectures have been generated that function as platforms for the dimerization, assembly,o rf unctional modulation of proteins,p roviding orthogonal control and reversible switching. [6][7][8][9][10] Theg eneration of orthogonal synthetic systems mimicking cellular components,v ia in vitro synthetic biological networks,c onstitutes al andmark objective.…”

Crystallographic and (spectro)electrochemical characterizations of cobalt(II) 10-phenyl-5,15-di-p-tolylporphyrin

“…Electrocatalytic four electrons reduction of O2 to H2O by cobalt porphyrins has been extensively studied so far not only because of its biological relevance, but also due to its technological significance such as in fuel cells [21,22]. Furthermore, the studies of cobalamin and its derivatives/analogues have significantly contributed to increase the popularity of Co(II) complexes [23][24][25][26]. It was also found that the reactivity of axial ligation of cobalt porphyrin play a pivotal role in a number of bio-and 'bio-inspired' catalytic transformations.…”