摘要
Calmodulin (CaM) is a multifunctional Ca2+-binding protein regulating the activity of many enzymes in response to fluctuation of the intracellular Ca2+ level. It has been shown that a CaM Q41C/K75C mutant (CaMSS) with a disulfide bond in the N-terminal domain exhibits greatly reduced affinity to Ca2+. In the present study, the experimental results revealed a unique metal binding pattern in CaMSS towards La3+ and Ca2+ separately: the mutant protein binds Ca2+ at site Ⅰ, Ⅲ and IV; however, it binds La3+ at site Ⅰ, Ⅱ and IV. A putative mechanism was proposed which is the conformation of site Ⅱ (or siteⅢ) of CaMSS could be altered and thus loses its metal ion affinity in response to metal binding in the opposite terminal domain possibly through the long range domain interaction. The present work may offer new perspectives for understanding the mechanisms of specific metal ion affinity in CaM and for CaM-based protein design.
Calmodulin (CaM) is a multifunctional Ca2+-binding protein regulating the activity of many enzymes in response to fluctuation of the intracellular Ca2+ level. It has been shown that a CaM Q41C/K75C mutant (CaMSS) with a disulfide bond in the N-terminal domain exhibits greatly reduced affinity to Ca2+. In the present study, the experimental results revealed a unique metal binding pattern in CaMSS towards La3+ and Ca2+ separately: the mutant protein binds Ca2+ at site Ⅰ, Ⅲ and IV; however, it binds La3+ at site Ⅰ, Ⅱ and IV. A putative mechanism was proposed which is the conformation of site Ⅱ (or siteⅢ) of CaMSS could be altered and thus loses its metal ion affinity in response to metal binding in the opposite terminal domain possibly through the long range domain interaction. The present work may offer new perspectives for understanding the mechanisms of specific metal ion affinity in CaM and for CaM-based protein design.
基金
support from the National Natural Science Foundation of China (Grant Nos. 20671008 & 20637010)
the Key Construction Program of the National "985" Project
