CHEMISTRY: Shaped by a Protein

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Science  11 May 2007:
Vol. 316, Issue 5826, pp. 801a
DOI: 10.1126/science.316.5826.801a

Hydrogels consist of water-soluble cross-linked polymers that can change properties such as their degree of swelling in response to changes in temperature, acidity, or ionic strength. Murphy et al. explored the use of a protein, calmodulin, as the active component of their gel systems. In the presence of calcium ions, calmodulin adopts an extended dumbbell shape that collapses upon the binding of certain ligands. The authors engineered a calmodulin variant with the tyrosine residues at the ends of the dumbbell motif replaced by cysteines. The two cysteine residues were separated by 50 Å in the extended configuration but only by 15 Å in the collapsed form. The engineered calmodulin was then incorporated through reaction of the cysteine side chains into a poly(ethylene glycol) (PEG) hydrogel. By treatment with a peptide ligand and subsequent washing, the incorporated protein could be cycled repeatedly between the two conformations, leading to an overall gel volume change on the order of 10 to 20%. Although this change is comparatively small in the hydrogel context, the authors note that the system was far from optimized, and that there are more than 200 well-characterized protein motions that might be adapted into functional gels. — MSL

Angew. Chem. Int. Ed. 46, 3066 (2007).

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