title: Intracellular pH modulates quinary structure.
abstract: NMR spectroscopy can provide information about proteins in living cells. pH is an important characteristic of the intracellular environment because it modulates key protein properties such as net charge and stability. Here, we show that pH modulates quinary interactions, the weak, ubiquitous interactions between proteins and other cellular macromolecules. We use the K10H variant of the B domain of protein G (GB1, 6.2 kDa) as a pH reporter in Escherichia coli cells. By controlling the intracellular pH, we show that quinary interactions influence the quality of in-cell (15) N-(1) H HSQC NMR spectra. At low pH, the quality is degraded because the increase in attractive interactions between E. coli proteins and GB1 slows GB1 tumbling and broadens its crosspeaks. The results demonstrate the importance of quinary interactions for furthering our understanding of protein chemistry in living cells.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, 27599.
authors.forename: Rachel D
authors.initials: RD
authors.lastname: Cohen
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, 27599.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Guseman
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina, 27599.|Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina, 27599.|Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina, 27599.
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Pielak
mesh_terms: D000577:Amides / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D042541:Intracellular Space; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D055550:Protein Stability; D011522:Protons
chemical_list: D000577:Amides; D029968:Escherichia coli Proteins; D011522:Protons
keywords: amide proton exchange; in-cell NMR; macromolecular crowding; pH; protein stability; quinary interactions