Structural properties of UMP-Kinase from escherichia coli :  modulation of protein solubility by pH and UTP

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DOIResolve DOI: http://doi.org/10.1021/bi960062v
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TypeArticle
Journal titleBiochemistry
ISSN0006-2960
1520-4995
Volume35
Issue22
Pages70037011; # of pages: 9
AbstractUMP-kinase from Escherichia coli, unlike the analogous enzyme from eukaryotic organisms, is an oligomeric protein subjected to complex regulatory mechanisms in which UTP and GTP act as allosteric effectors. While the enzyme has an unusually low solubility at neutral pH (≤0.1 mg of protein/mL), its solubility increases markedly above pH 8 and below pH 4. Furthermore, the solubility of the bacterial UMP-kinase at neutral pH is greatly enhanced in the presence of Mg-free UTP. Thermal denaturation experiments have demonstrated that UTP also increases the stability of the protein. Fourier-transform infrared spectroscopy and circular dichroism show that the secondary structure of the protein is the same at neutral and at alkaline pH. These data indicate that variations in enzyme solubility must be related to subtle changes in the tertiary and/or quaternary structure which modulate the exposure of hydrophobic surfaces in the protein molecule. A variant of UMP-kinase, obtained by site-directed mutagenesis (Asp159Asn), which is similar to the wild-type enzyme in its stability and kinetic properties, has a much increased water solubility (>5 mg protein/mL) even at neutral pH. This suggests that salt bridges may be involved in the equilibrium between the soluble and aggregated forms of the wild-type enzyme, and that conformational changes induced upon binding of UTP increase the protein solubility by disrupting these salt bridges.
Publication date
PublisherAmerican Chemical Society
AffiliationNRC Institute for Biodiagnostics; National Research Council Canada
Peer reviewedYes
NRC number414
NPARC number9148403
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Record identifiera26373e6-dae3-4fc6-8289-afab3e63adab
Record created2009-06-25
Record modified2016-11-10
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