Signal transduction versus buffering activity in Ca2+–binding proteins

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Abstract
The three-dimensional structure of calbindin D9k in the absence of Ca2+ has been determined using NMR spectroscopy in solution, allowing the first direct analysis of the consequences of Ca2+ binding for a member of the calmodulin superfamily of proteins. The overall response in calbindin D9k is much attenuated relative to the current model for calmodulin and troponin C. These results demonstrate a novel mechanism for modulating the conformational response to Ca(2+)-binding in calmodulin superfamily proteins and provide insights into how their Ca(2+)-binding domains can be fine-tuned to remain essentially intact or respond strongly to ion binding, in relation to their functional requirements.