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Genetically encoded bright Ca2+ probe applicable for dynamic Ca2+ imaging of dendritic spines
Masamichi Ohkura1, Masanori Matsuzaki, Haruo Kasai
1Department of Information Physiology, and Department of Cell Physiology, National Institute for Physiological Sciences, and School of Life Science, Graduate University for Advanced Studies, Okazaki, Aichi 444-8585, Japan.
Analytical Chemistry
|September 15, 2005
Summary
Researchers developed G-CaMP1.6, a brighter and more pH-stable calcium (Ca2+) probe. This improved green fluorescent protein-based sensor allows for easier detection of intracellular Ca2+ signals, even in small neuronal structures.
Area of Science:
- Biochemistry
- Molecular Biology
- Neuroscience
Background:
- Single green fluorescent protein (GFP)-based calcium (Ca2+) probes like G-CaMP offer valuable tools for monitoring cellular Ca2+ dynamics.
- However, existing probes often suffer from low fluorescence intensity and sensitivity to pH changes, limiting their utility.
- There is a need for enhanced Ca2+ probes with improved brightness, stability, and specificity.
Purpose of the Study:
- To develop an improved G-CaMP variant with enhanced fluorescence and reduced pH sensitivity for more reliable intracellular Ca2+ detection.
- To characterize the Ca2+ sensitivity, selectivity, and buffering capacity of the novel probe.
- To demonstrate the probe's efficacy in detecting Ca2+ signals in mammalian cells and neuronal structures.
Main Methods:
- Protein engineering of G-CaMP by introducing specific mutations to enhance fluorescence quantum yield and Ca2+ binding properties.
- Biochemical characterization of the G-CaMP1.6 probe, including measurements of fluorescence intensity, pH sensitivity, and Ca2+ affinity (Kd, Hill coefficient).
- Expression of G-CaMP1.6 in mammalian cells and primary neurons to visualize intracellular Ca2+ dynamics in response to stimuli and in subcellular compartments like dendritic spines.
Main Results:
- G-CaMP1.6 exhibits approximately 40-fold higher fluorescence intensity compared to the original G-CaMP due to increased quantum yield.
- The novel probe demonstrates significantly lower pH sensitivity and higher selectivity for Ca2+ over other divalent cations.
- G-CaMP1.6 successfully detected local Ca2+ changes in dendritic spines, a feat not previously achieved with GFP-based probes.
- Mutations in Ca2+-binding sites, such as in G-CaMP1.6-CaM(E140K), further improved brightness and reduced Ca2+-buffering capacity.
Conclusions:
- G-CaMP1.6 represents a significant advancement in GFP-based Ca2+ probes, offering superior brightness and pH stability.
- The enhanced probe facilitates easier and more sensitive detection of intracellular Ca2+ signals, enabling novel biological discoveries.
- G-CaMP1.6 and its variants are powerful tools for neuroscience research, particularly for studying Ca2+ dynamics in fine neuronal structures.