Publications by authors named "Iryna Mahorivska"

2 Publications

  • Page 1 of 1

Zinc modulation of proton currents in a new voltage-gated proton channel suggests a mechanism of inhibition.

FEBS J 2020 11 6;287(22):4996-5018. Epub 2020 Apr 6.

Institut für Physiologie und Pathophysiologie, Paracelsus Universität Salzburg Standort Nürnberg, Nuremberg, Germany.

The H 1 voltage-gated proton (H 1) channel is a key component of the cellular proton extrusion machinery and is pivotal for charge compensation during the respiratory burst of phagocytes. The best-described physiological inhibitor of H 1 is Zn . Externally applied ZnCl drastically reduces proton currents reportedly recorded in Homo sapiens, Rattus norvegicus, Mus musculus, Oryctolagus cuniculus, Rana esculenta, Helix aspersa, Ciona intestinalis, Coccolithus pelagicus, Emiliania huxleyi, Danio rerio, Helisoma trivolvis, and Lingulodinium polyedrum, but with considerable species variability. Here, we report the effects of Zn and Cd on H 1 from Nicoletia phytophila, NpH 1. We introduced mutations at potential Zn coordination sites and measured Zn inhibition in different extracellular pH, with Zn concentrations up to 1000 μm. Zn inhibition in NpH 1 was quantified by the slowing of the activation time constant and a positive shift of the conductance-voltage curve. Replacing aspartate in the S3-S4 loop with histidine (D145H) enhanced both the slowing of activation kinetics and the shift in the voltage-conductance curve, such that Zn inhibition closely resembled that of the human channel. Histidine is much more effective than aspartate in coordinating Zn in the S3-S4 linker. A simple Hodgkin Huxley model of NpH 1 suggests a decrease in the opening rate if it is inhibited by zinc or cadmium. Limiting slope measurements and high-resolution clear native gel electrophoresis (hrCNE) confirmed that NpH 1 functions as a dimer. The data support the hypothesis that zinc is coordinated in between the dimer instead of the monomer. Zinc coordination sites may be potential targets for drug development.
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November 2020

Antibody-mediated sialidase activity in blood serum of patients with multiple myeloma.

J Mol Recognit 2011 Jul-Aug;24(4):576-84. Epub 2010 Nov 16.

Institute of Cell Biology, National Academy of Sciences of Ukraine, Lviv 79005, Ukraine.

Cell surface sialylation is known to be tightly connected with tumorigenicity, invasiveness, metastatic potential, clearance of aged cells, while the sialylation of IgG molecules determines their anti-inflammatory properties. Four sialidases - hydrolytic enzymes responsible for cleavage of sialic residues - were described in different cellular compartments. However, sialidases activity in body fluids, and specifically in blood serum, remains poorly studied. Here, we characterize first known IgG antibodies possessing sialidase-like activity in blood serum of multiple myeloma (MM) patients. Ig fractions were precipitated with ammonium sulfate (50% of saturation) from blood serum of 12 healthy donors and 14 MM patients, and screened for the presence of sialidase activity by using 4-MUNA (2'-(4-methylumbelliferyl)-α-D-N-acetylneuraminic acid) as substrate. High level of sialidase activity was detected in the MM patients, but not in healthy donors. Subsequent antibody purification by protein-G affinity chromatography and HPLC size exclusion chromatography at acidic conditions demonstrated that sialidase activity was attributable to IgG molecules. Sialidase activity was also specific for (Fab)(2) fragment of IgG and blocked by sialidase inhibitor DANA. Sialidase activity of IgG molecule was also confirmed by in gel assay for cleavage of sialidase substrate. Kinetic parameters of the catalysis reaction were described by Michaelis-Menten equation with K(m)  = 44.4-108 µM and k(cat) = 2.7-23.1 min(-1). The action of IgG possessing sialidase-like activity towards human red blood cells resulted in a subsequent increase in their agglutination by the peanut agglutinin, that confirms their desialylation by the studied IgG. This is the first demonstration of the intrinsic sialidase activity of IgG isolated from blood serum of MM patients.
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September 2011