2. Academic Validation
  3. Relative Cosolute Size Influences the Kinetics of Protein-Protein Interactions

Relative Cosolute Size Influences the Kinetics of Protein-Protein Interactions

  • Biophys J. 2015 Aug 4;109(3):510-20. doi: 10.1016/j.bpj.2015.06.043.
Laurel Hoffman 1,  Xu Wang 2,  Hugo Sanabria 3,  Margaret S Cheung 4,  John A Putkey 2,  M Neal Waxham 5
Affiliations

Affiliations

  • 1 Department of Neurobiology and Anatomy, University of Texas Medical School at Houston, Houston, Texas.
  • 2 Department of Biochemistry and Molecular Biology, University of Texas Medical School at Houston, Houston, Texas.
  • 3 Department of Physics and Astronomy, Clemson University, Clemson, South Carolina.
  • 4 Department of Physics, University of Houston, Houston, Texas; The Center for Theoretical Biological Physics, Rice University, Houston, Texas.
  • 5 Department of Neurobiology and Anatomy, University of Texas Medical School at Houston, Houston, Texas. Electronic address: m.n.waxham@uth.tmc.edu.
PMID: 26244733 DOI: 10.1016/j.bpj.2015.06.043
Abstract

Protein signaling occurs in crowded intracellular environments, and while high concentrations of macromolecules are postulated to modulate protein-protein interactions, analysis of their impact at each step of the reaction pathway has not been systematically addressed. Potential cosolute-induced alterations in target association are particularly important for a signaling molecule like Calmodulin (CaM), where competition among >300 targets governs which pathways are selectively activated. To explore how high concentrations of cosolutes influence CaM-target affinity and kinetics, we methodically investigated each step of the CaM-target binding mechanism under crowded or osmolyte-rich environments mimicked by ficoll-70, dextran-10, and sucrose. All cosolutes stabilized compact conformers of CaM and modulated association kinetics by affecting diffusion and rates of conformational change; however, the results showed that differently sized molecules had variable effects to enhance or impede unique steps of the association pathway. On- and off-rates were modulated by all cosolutes in a compensatory fashion, producing little change in steady-state affinity. From this work insights were gained on how high concentrations of inert crowding agents and osmolytes fit into a kinetic framework to describe protein-protein interactions relevant for cellular signaling.

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