Both the C-terminal polylysine region and the farnesylation of K-RasB are important for its specific interaction with calmodulin.
PLoS One 2011;
6:e21929. [PMID:
21750741 PMCID:
PMC3130059 DOI:
10.1371/journal.pone.0021929]
[Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 06/09/2011] [Indexed: 02/03/2023] Open
Abstract
Background
Ras protein, as one of intracellular signal switches, plays various roles in several cell activities such as differentiation and proliferation. There is considerable evidence showing that calmodulin (CaM) binds to K-RasB and dissociates K-RasB from membrane and that the inactivation of CaM is able to induce K-RasB activation. However, the mechanism for the interaction of CaM with K-RasB is not well understood.
Methodology/Principal Findings
Here, by applying fluorescence spectroscopy and isothermal titration calorimetry, we have obtained thermodynamic parameters for the interaction between these two proteins and identified the important elements of K-RasB for its interaction with Ca2+/CaM. One K-RasB molecule interacts with one CaM molecule in a GTP dependent manner with moderate, micromolar affinity at physiological pH and physiologic ionic strength. Mutation in the polybasic domain of K-Ras decreases the binding affinity. By using a chimera in which the C-terminal polylysine region of K-RasB has been replaced with that of H-Ras and vice versa, we find that at physiological pH, H-Ras-(KKKKKK) and Ca2+/CaM formed a 1∶1 complex with an equilibrium association constant around 105 M−1, whereas no binding reaction of K-RasB-(DESGPC) with Ca2+/CaM is detected. Furthermore, the interaction of K-RasB with Ca2+/CaM is found to be enhanced by the farnesylation of K-RasB.
Conclusions/Significance
We demonstrate that the polylysine region of K-RasB not only contributes importantly to the interaction of K-RasB with Ca2+/CaM, but also defines its isoform specific interaction with Ca2+/CaM. The farnesylation of K-RasB is also important for its specific interaction with Ca2+/CaM. Information obtained here can enhance our understanding of how CaM interacts with K-RasB in physiological environments.
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