The Effect of Fluorescent Protein Tags on Phosphoglycerate Kinase Stability Is Nonadditive

Kapil Dave, Hannah Gelman, Chu Thi Hien Thu, Drishti Guin, Martin Gruebele

Research output: Contribution to journalArticle


It is frequently assumed that fluorescent protein tags used in biological imaging experiments are minimally perturbing to their host protein. As in-cell experiments become more quantitative and measure rates and equilibrium constants, rather than just "on-off" activity or the presence of a protein, it becomes more important to understand such perturbations. One criterion for a protein modification to be a perturbation is additivity of two perturbations (a linear effect on the protein free energy). Here we show that adding fluorescent protein tags to a host protein in vitro has a large nonadditive effect on its folding free energy. We compare an unlabeled, three singly labeled, and a doubly labeled enzyme (phosphoglycerate kinase). We propose two mechanisms for nonadditivity. In the "quinary interaction" mechanism, two tags interact transiently with one another, relieving the host protein from unfavorable tag-protein interactions. In the "crowding" mechanism, adding two tags provides the minimal crowding necessary to overcome destabilizing interactions of individual tags with the host protein. Both of these mechanisms affect protein stability in cells; we show here that they must also be considered for tagged proteins used for reference in vitro. (Figure Presented).

Original languageEnglish (US)
Pages (from-to)2878-2885
Number of pages8
JournalJournal of Physical Chemistry B
Issue number11
StatePublished - Mar 24 2016

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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