Nature Materials 2, 600–604 (2003)

In the above paper, we reported that the threshold concentration of free Ca2+ required to induce longitudinal contraction in forisomes was in the nanomolar range. Due to errors in estimating Ca2+ concentrations in Ca2+-buffered media, these calculated figures were incorrect. Recent tests in our lab have shown that the threshold concentration varies between 60 and 90 μM under the conditions originally described. We wish to stress that this clarification does not bear on our conclusions regarding the biological function of forisomes and the technological potential of forisome-like proteinaceous smart materials. For a technical discussion of errors of the type we made, the reader is referred to C. Patton et al. (Cell Calcium 35, 427–431; 2004).