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报告内容摘要：
Ca2+ channels and calmodulin (CaM) are prominent hubs of signaling networks, extensively coordinated by feedback control. For example, each channel associates with its own CaM (but see PNAS 106:5135), acting as a Ca2+ sensor that regulates Ca2+ entry through channels. Because channels bind CaM avidly, every channel should possess CaM and exhibit regulation, regardless of biological fluctuations of CaM concentration. This would represent a significant form of concentration independence between Ca2+ channels and CaM. Here, we reveal significant exceptions to this autonomy, by combining electrophysiology to characterize channel regulation, with concurrent optical FRET sensor determination of free apoCaM concentration in live cells. This approach translates quantitative CaM biochemistry from the traditional test-tube context, into the realm of functioning holochannels within intact cells. From this perspective, we find that long splice forms of CaV1.3 and CaV1.4 channels include a distalcarboxy-tail module that functions like an enzyme inhibitor to retune channel affinity for apoCaM. In this configuration, natural CaM variations alter Ca2+ feedback gain, and the strength of competitive retuning is customized across channel subtypes (CaV1.3 versus CaV1.4), and species (rat versus human CaV1.3). Given the ubiquity of these channels, the corresponding connections between ambient CaM levels and Ca2+ entry via channels are broadly significant for Ca2+ homeostasis---presumed alterations of apoCaM levels in neurodegenerative conditions like Parkinson’s and Alzheimer’s are predicted to increase Ca2+ entry, potentially explaining the Ca2+ dysfunction underlying these diseases. Mechanistically, our extensions of enzyme inhibitor analysis argue well that the competitive retuning in holochannels indeed reflects competition between a single distal carboxy tail module and a single CaM molecule, both vying for IQ domain occupancy on channels.

报告人简介：
     Professor of Biomedical Engineering and Neuroscience, John Hopkins University School of Medicine.  His research interests are as follows. Molecular Engineering Physiology of Ca2+ Channels and Ca2+ Signals Intracellular Ca2+ signals comprise a lingua franca of life at the microscopic scale. For example, Ca2+ inflow through Ca2+ channels (a voltage-controlled, Ca2+-entry porthole into cells) starts a chain of events leading to initiation of the heartbeat, or even to the neuro-synaptic transmission underlying our very thoughts. Moreover, longer-term changes in [Ca2+] control gene expression. It is no wonder that Ca2+ signals are as critical and ubiquitous to biological systems, as are voltage signals to electronic circuits. Much of our research therefore focuses on the “transistors” of Ca2+ signaling?voltage-gated Ca2+ channels. Unmasking their secrets critically deepens understanding of normal biology, and promises to reveal new therapies for disease.
     Ca2+ signals research provides a remarkable opportunity for the fruitful combination of mathematics, engineering, and molecular experimentation. Channel functions can be quantitatively probed with patch-clamp electrophysiology (1-4) and a biological fluorescence technique called FRET (3). The latter approach offers a dynamic readout of molecular motions in single living cells. Molecular biology (1-4), biochemistry (1-3), and virology (4) permit exquisite molecular manipulation of channels. Experiments and theory are wedded with mathematical modeling (1).
     Calmodulin – a central Ca2+-sensing molecule in biology – is comprised of two ball-like ends attached by a flexible linker. We have discovered a key rationale for this mysterious bio-architectural design: each ball selectively demodulates different streams of information from a common Ca2+ signal, and then each ball appropriately affects channel function in a distinct way (1- 3). Such features make calmodulin the biological equivalent of a stereo receiver, capable of extracting two channels of information from a common radio signal.