2 research outputs found
Role of the Surface-Exposed Leucine 155 in the Metal Ion Binding Loop of the CuA Domain of Cytochrome <i>c</i> Oxidase from <i>Thermus thermophilus</i> on the Function and Stability of the Protein
The role of Leu155 in the metal ion binding loop in the
soluble CuA binding domain of subunit II of cytochrome <i>c</i> oxidase from <i>Thermus thermophilus</i> (TtCuA) was investigated
by site-specific mutations of this residue to arginine (L155R) and
glutamic acid (L155E). The UV–visible absorption and electron
paramagnetic resonance spectra suggested that the Cu<sub>2</sub>S<sub>2</sub> core of TtCuA was almost unchanged by the mutations. The
redox potential of the metal center in the L155R mutant was ∼20
mV higher than that in the WT protein, while that of the L155E mutant
was almost the same as that of the wild type (WT-TtCuA). The rate
of transfer of an electron from cytochrome <i>c</i><sub>552</sub> to the L155E mutant was much lower than that of transfer
to the WT protein, while that for transfer to the L155R mutant was
similar to that of WT-TtCuA. The total reorganization energy was increased
for both the mutant proteins compared to WT-TtCuA. The results suggest
that the presence of a negatively charged residue at the site of Leu155
in TtCuA possibly disfavors the protein–protein interaction
between the two redox partners. The mutation also affected the equilibrium
pH dependence of the protein. The thermal and thermodynamic stability
of TtCuA was drastically decreased upon the mutation, which is most
prominent in the L155R mutant. These studies indicate that the hydrophobic
patch at the surface of TtCuA consisting of Leu155 is important for
the transfer of an electron between cytochrome <i>c</i><sub>552</sub> and TtCuA
Synthesis, crystal structure and spectroscopic and electrochemical properties of bridged trisbenzoato copper-zinc heterobinuclear complex of 2,2 `-bipyridine
The synthesis of the heterobinuclear copper-zinc complex CuZn(bz)(3)(bpy)(2)]ClO4 (bz = benzoate) from benzoic acid and bipyridine is described. Single crystal X-ray diffraction studies of the heterobinuclear complex reveals the geometry of the benzoato bridged Cu(II)-Zn(II) centre. The copper or zinc atom is pentacoordinate, with two oxygen atoms from bridging benzoato groups and two nitrogen atoms from one bipyridine forming an approximate plane and a bridging oxygen atom from a monodentate benzoate group. The Cu-Zn distance is 3.345 angstrom. The complex is normal paramagnetic having mu(eff) value equal to 1.75 BM, ruling out the possibility of Cu-Cu interaction in the structural unit. The ESR spectrum of the complex in CH3CN at RT exhibit an isotropic four line spectrum centred at g = 2.142 and hyperfine coupling constants A(av) = 63 x 10(-4) cm(-1), characteristic of a mononuclear square-pyramidal copper(II) complexes. At LNT, the complex shows an isotropic spectrum with g(parallel to) = 2.254 and g(perpendicular to) =2.071 and A(parallel to) = 160 x 10(-4) cm(-1). The Hamiltonian parameters are characteristic of distorted square pyramidal geometry. Cyclic voltammetric studies of the complex have indicated quasi-reversible behaviour in acetonitrile solution. (C) 2014 Elsevier B.V. All rights reserved