80 research outputs found
A New Heterobinuclear FeIIICuII Complex with a Single Terminal FeIII–O(phenolate) Bond. Relevance to Purple Acid Phosphatases and Nucleases
A novel heterobinuclear mixed valence complex [Fe^IIICu^II(BPBPMP)(OAc)_2]ClO_4, 1, with the unsymmetrical N_5O_2 donor ligand 2-bis[{(2-pyridylmethyl)aminomethyl}-6-{(2-hydroxybenzyl)(2-pyridylmethyl)} aminomethyl]-4-methylphenol (H_2BPBPMP) has been synthesized and characterized. A combination of data from mass spectrometry, potentiometric titrations, X-ray absorption and electron paramagnetic resonance spectroscopy, as well as kinetics measurements indicates that in ethanol/water solutions an [Fe^III-(nu)OH-Cu^IIOH_2]+ species is generated which is the likely catalyst for 2,4-bis(dinitrophenyl)phosphate and DNA hydrolysis. Insofar as the data are consistent with the presence of an Fe_III-bound hydroxide acting as a nucleophile during catalysis, 1 presents a suitable mimic for the hydrolytic enzyme purple acid phosphatase. Notably, 1 is significantly more reactive than its isostructural homologues with different metal composition (Fe^IIIM^II, where M^II is Zn^II, Mn^II, Ni^II,or Fe^II). Of particular interest is the observation that cleavage of double-stranded plasmid DNA occurs even at very low concentrations of 1 (2.5 nuM), under physiological conditions (optimum pH of 7.0), with a rate enhancement of 2.7 x 10^7 over the uncatalyzed reaction. Thus, 1 is one of the most effective model complexes to date, mimicking the function of nucleases
Comparison of the Backbone Dynamics of Dehaloperoxidase-Hemoglobin Isoenzymes
Dehaloperoxidase (DHP) is a multifunctional hemeprotein
with a
functional switch generally regulated by the chemical class of the
substrate. Its two isoforms, DHP-A and DHP-B, differ by only five
amino acids and have an almost identical protein fold. However, the
catalytic efficiency of DHP-B for oxidation by a peroxidase mechanism
ranges from 2- to 6-fold greater than that of DHP-A depending on the
conditions. X-ray crystallography has shown that many substrates and
ligands have nearly identical binding in the two isoenzymes, suggesting
that the difference in catalytic efficiency could be due to differences
in the conformational dynamics. We compared the backbone dynamics
of the DHP isoenzymes at pH 7 through heteronuclear relaxation dynamics
at 11.75, 16.45, and 19.97 T in combination with four 300 ns MD simulations.
While the overall dynamics of the isoenzymes are similar, there are
specific local differences in functional regions of each protein.
In DHP-A, Phe35 undergoes a slow chemical exchange between two conformational
states likely coupled to a swinging motion of Tyr34. Moreover, Asn37
undergoes fast chemical exchange in DHP-A. Given that Phe35 and Asn37
are adjacent to Tyr34 and Tyr38, it is possible that their dynamics
modulate the formation and migration of the active tyrosyl radicals
in DHP-A at pH 7. Another significant difference is that both distal
and proximal histidines have a 15–18% smaller S2 value in DHP-B, thus their greater flexibility could
account for the higher catalytic activity. The distal histidine grants
substrate access to the distal pocket. The greater flexibility of
the proximal histidine could also accelerate H2O2 activation at the heme Fe by increased coupling of an amino acid
charge relay to stabilize the ferryl Fe(IV) oxidation state in a Poulos-Kraut
“push–pull”-type peroxidase mechanism
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