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Poly(zwitterionic)protein conjugates offer increased stability without sacrificing binding affinity or bioactivity


Treatment with therapeutic proteins is an attractive approach to targeting a number of challenging diseases. Unfortunately, the native proteins themselves are often unstable in physiological conditions, reducing bioavailability and therefore increasing the dose that is required. Conjugation with poly(ethylene glycol) (PEG) is often used to increase stability, but this has a detrimental effect on bioactivity. Here, we introduce conjugation with zwitterionic polymers such as poly(carboxybetaine). We show that poly(carboxybetaine) conjugation improves stability in a manner similar to PEGylation, but that the new conjugates retain or even improve the binding affinity as a result of enhanced protein–substrate hydrophobic interactions. This chemistry opens a new avenue for the development of protein therapeutics by avoiding the need to compromise between stability and affinity.

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Figure 1: Stability of PEG, pCB Mn (similar molecular weight) and pCB Rh (similar hydrodynamic size) conjugated with enzyme CT.
Figure 2: Affinities of prepared conjugates measured as Michaelis constants Km.
Figure 3: Mechanism of how PEG and pCB polymers influence binding affinity.


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This work was supported by the Office of Naval Research (N000140910137 and N000141010600) and the National Science Foundation (DMR-1005699). A.J.K. was partially supported through a National Cancer Institute training grant (T32CA138312). The authors thank the members of the Jiang research group, especially Zhiqiang Cao and Hong Xue, for helpful discussions.

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A.J.K. performed all the experiments presented in this work. A.J.K. and S.J. designed the experiments and prepared the manuscript.

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Correspondence to Shaoyi Jiang.

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The authors declare no competing financial interests.

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Keefe, A., Jiang, S. Poly(zwitterionic)protein conjugates offer increased stability without sacrificing binding affinity or bioactivity. Nature Chem 4, 59–63 (2012).

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