Common crowding agents have only a small effect on protein-protein interactions

Yael Phillip, Eilon Sherman, Gilad Haran, Gideon Schreiber*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

114 Scopus citations


Studies of protein-protein interactions, carried out in polymer solutions, are designed to mimic the crowded environment inside living cells. It was shown that crowding enhances oligomerization and polymerization of macromolecules. Conversely, we have shown that crowding has only a small effect on the rate of association of protein complexes. Here, we investigated the equilibrium effects of crowding on protein heterodimerization of TEM1-β-lactamase with β-lactamase inhibitor protein (BLIP) and barnase with barstar. We also contrasted these with the effect of crowding on the weak binding pair CyPet-YPet. We measured the association and dissociation rates as well as the affinities and thermodynamic parameters of these interactions in polyethylene glycol and dextran solutions. For TEM1-BLIP and for barnase-barstar, only a minor reduction in association rate constants compared to that expected based on solution viscosity was found. Dissociation rate constants showed similar levels of reduction. Overall, this resulted in a binding affinity that is quite similar to that in aqueous solutions. On the other hand, for the CyPet-YPet pair, aggregation, and not enhanced dimerization, was detected in polyethylene glycol solutions. The results suggest that typical crowding agents have only a small effect on specific protein-protein dimerization reactions. Although crowding in the cell results from proteins and other macromolecules, one may still speculate that binding in vivo is not very different from that measured in dilute solutions.

Original languageAmerican English
Pages (from-to)875-885
Number of pages11
JournalBiophysical Journal
Issue number3
StatePublished - 2009
Externally publishedYes

Bibliographical note

Funding Information:
This research was partially supported by the Clore Center for Biological Physics (grant No. 1609).


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