Christine Wiebe Buchanan | University of Alberta (original) (raw)

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Papers by Christine Wiebe Buchanan

Na+}H+ exchangers are a family of ubiquitous membrane proteins. In higher eukaryotes they regulat... more Na+}H+ exchangers are a family of ubiquitous membrane proteins. In higher eukaryotes they regulate cytosolic pH by removing an intracellular H+ in exchange for an extracellular Na+. In yeast and Escherichia coli, Na+}H+ exchangers function in the opposite direction to remove intracellular Na+ in exchange for extracellular H+. Na+}H+ exchangers display an internal pH-sensitivity that varies with the different antiporter types. Only recently have investigations examined the amino acids involved in pH-sensitivity and in cation binding and transport. Histidine residues are good candidates for H+-sensing amino acids, since they can ionize within the physiological pH range. Histidine residues have been shown to be important in the function of the E. coli Na+}H+ exchanger NhaA and in the yeast Na+}H+ exchanger sod2. In E. coli, His## & of NhaA may function to interact with, or regulate, the pH-sensory region of NhaA. In 1.

Molecular and cellular biochemistry, 2003

The Na+/H+ exchanger is an integral membrane protein found in the plasma membrane of eukaryotic a... more The Na+/H+ exchanger is an integral membrane protein found in the plasma membrane of eukaryotic and prokaryotic cells. In eukaryotes it functions to exchange one proton for a sodium ion. In mammals it removes intracellular protons while in plants and fungal cells the plasma membrane form removes intracellular sodium in exchange for extracellular protons. In this study we used the Na+/H+ exchanger of Schizosaccharomyces pombe (Sod2) as a model system to study amino acids critical for activity of the protein. Twelve mutant forms of the Na+/H+ exchanger were examined for their ability to translocate protons as assessed by a Cytosensor microphysiometer. Mutation of the amino acid Histidine 367 resulted in defective proton translocation. The acidic residues Asp145, Asp178, Asp266 and Asp267 were important in the proton translocation activity of the Na+/H+ exchanger. Mutation of amino acids His98, His233 and Asp241 did not significantly impair proton translocation by the Na+/H+ exchanger....

Canadian Journal of Physiology and Pharmacology, 2005

In the fission yeast Schizosaccharomyces pombe, the Na+/H+ exchanger, Sod2, plays a major role in... more In the fission yeast Schizosaccharomyces pombe, the Na+/H+ exchanger, Sod2, plays a major role in the removal of excess intracellular sodium, and its disruption results in a sodium-sensitive phenotype. We examined the subcellular distribution and dynamics of Sod2 expression in S. pombe using a sod2-GFP fusion protein under the control of an attenuated version of the inducible nmt promoter. Sod2 was localized throughout the plasma membrane, the nuclear envelope, and some internal membrane systems. In exponentially growing cells, in which sod2-GFP was expressed and then the promoter turned-off, previously synthesized sod2-GFP was stable for long periods and found localized to the plasma membrane in the medial regions of the cell. It was not present at the actively growing cell ends. This suggests that these regions of the cell contain old plasma membrane protein vs. newly synthesized plasma membrane without Sod2 at the growing ends. Sod2 localization was not affected by salt stress. T...

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Canadian Journal of Microbiology, 1995

The purpose of this study was to determine the ability of nonbasidiomycete soil fungi to oxidize ... more The purpose of this study was to determine the ability of nonbasidiomycete soil fungi to oxidize pyrene (four rings) and benzo[a]pyrene (BaP) (five rings). Fungi were isolated from five different soils in which the polycyclic aromatic hydrocarbon content ranged from 0.8 to 80 μg/g dry soil. Approximately 50% of the isolates in all sites were able to oxidize pyrene. The pyrene-oxidizing species belonged to all fungal divisions except basidiomycetes. The most common were Penicillium spp. of the subgenus Furcatum and these dominated the more contaminated soils. Penicillium janthinellum and Syncephalastrum racemosum exhibited the most rapid rates of pyrene oxidation. The major pyrene metabolites were identified by proton NMR and mass spectrometry as 1-pyrenol, 1,6- and 1,8-pyrenediol, and the 1,6- and 1,8-pyrenequinones. A high correlation was found between the ability to oxidize pyrene and BaP. As with pyrene, approximately 50% of the fungal isolates tested oxidized BaP to 9-hydroxy-Ba...

Biochemistry and cell biology, 1999

This study reports the cloning and characterization of a cDNA encoding elongation factor 1-alpha ... more This study reports the cloning and characterization of a cDNA encoding elongation factor 1-alpha (EF1alpha) from the yeast Schizosaccharomyces pombe. The cDNA was cloned from an Schizosaccharomyces pombe expression library by a two-hybrid selection for clones encoding calmodulin (CaM)-binding proteins. The predicted protein is highly homologous to mammalian EF1alpha, indicating a strong tendency towards conservation of the primary amino acid sequence. The protein was expressed as a glutathione S-transferase fusion in both bacteria and in Schizosaccharomyces pombe. The bacterial protein was shown by solution assay to compete with CaM kinase II for CaM. The CaM binding domain was localized to the C-terminus of the protein by this method. Expression of full-length EF1alpha in vivo caused an increase in cell cycle length and a decreased rate of growth as evidenced by a lack of elongated cells in slowly dividing cultures. This effect appears to involve CaM binding because a truncation mutant version of EF1alpha lacking the CaM binding domain did not cause cell cycle delay.Key words: calmodulin, two-hybrid selection, calmodulin-binding protein, yeast, cell proliferation.