Potassium Glutamate and Glycine Betaine Induce Self-Assembly of the PCNA and β-Sliding Clamps.

Autor:	Purohit A; School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, Arizona., Douma LG; Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida., Bloom LB; Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, Florida., Levitus M; School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, Arizona. Electronic address: marcia.levitus@asu.edu.
Jazyk:	angličtina
Zdroj:	Biophysical journal [Biophys J] 2021 Jan 05; Vol. 120 (1), pp. 73-85. Date of Electronic Publication: 2020 Nov 19.
DOI:	10.1016/j.bpj.2020.11.013
Abstrakt:	Sliding clamps are oligomeric ring-shaped proteins that increase the efficiency of DNA replication. The stability of the Escherichia coli β-clamp, a homodimer, is particularly remarkable. The dissociation equilibrium constant of the β-clamp is of the order of 10 pM in buffers of moderate ionic strength. Coulombic electrostatic interactions have been shown to contribute to this remarkable stability. Increasing NaCl concentration in the assay buffer results in decreased dimer stability and faster subunit dissociation kinetics in a way consistent with simple charge-screening models. Here, we examine non-Coulombic ionic effects on the oligomerization properties of sliding clamps. We determined relative diffusion coefficients of two sliding clamps using fluorescence correlation spectroscopy. Replacing NaCl by KGlu, the primary cytoplasmic salt in E. coli, results in a decrease of the diffusion coefficient of these proteins consistent with the formation of protein assemblies. The UV-vis spectrum of the β-clamp labeled with tetramethylrhodamine shows the characteristic absorption band of dimers of rhodamine when KGlu is present in the buffer. This suggests that KGlu induces the formation of assemblies that involve two or more rings stacked face-to-face. Results can be quantitatively explained on the basis of unfavorable interactions between KGlu and the functional groups on the protein surface, which drive biomolecular processes that bury exposed surface. Similar results were obtained with the Saccharomyces cerevisiae PCNA sliding clamp, suggesting that KGlu effects are not specific to the β-clamp. Clamp association is also promoted by glycine betaine, a zwitterionic compound that accumulates intracellularly when E. coli is exposed to high concentrations of extracellular solute. Possible biological implications are discussed. (Copyright © 2020 Biophysical Society. Published by Elsevier Inc. All rights reserved.)
Databáze:	MEDLINE
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