The current main research interest of my laboratory is voltage-gated Ca2+ channels (VGCCs), which deliver Ca2+ ions into neurons and other excitable cells in response to membrane depolarization and are vital for diverse physiological processes including muscle contraction, neurotransmitter release, neurodevelopment and gene expression. We use a combination of techniques including patch-clamp, molecular genetics, biochemistry, chemical modification and x-ray crystallography to study the structure, function, regulation, targeting and localization of these channels. The main areas of research are:
1. Regulation by PIP2. We recently discovered that PIP2 exerts two distinct and opposing actions on VGCCs: it is crucial for maintaining channel activity in intact cells and produces a strong voltage-dependent inhibition by altering the voltage-dependence of channel activation, an effect that can be prevented and reversed by PKA phosphorylation. We are investigating the molecular, cellular and physiological mechanisms underlying the dual actions of PIP2, identifying regions and amino acids that are involved in PIP2 binding and PKA phosphorylation, and testing the hypothesis that some well-known signaling pathways (such as G proteins and PKA) that regulate VGCCs in native neurons do so by altering PIP2-channel interactions.
2. Structure-function. We are studying the molecular architecture of the channel pore and the molecular mechanism of ion selectivity, permeation and gating. This line of research is similar to what we have done on inward rectifier K+ channels. Genetically altered channels are expressed heterologously in Xenopus oocytes and mammalian cells and studied with biophysical and electrophysiological methods. The questions we want to address include: Which regions and amino acids form the inner pore? Is the general architecture of VGCCs similar to that of K+ channels? Are the four glutamate residues critical for Ca2+ selectivity spatially displaced along the pore axis? Where is the voltage-dependent activation gate? We address these questions by determining the rate of block or covalent modification of cysteines engineered in the pore by various reagents in both the open and closed states.
3. Targeting and localization. Different types of VGCCs are differentially distributed in neurons. For example, the L-type channels are concentrated in the cell body whereas the N- and P/Q-type channels are localized in nerve terminals. The discrete localization is critical in determining the functions of these channels. We tag different type of VGCCs with various genetically encoded sensors, visualize them in living neurons with confocal and two-photon microscopy, and study the molecular mechanism underlying differential targeting and localization.
4. X-ray crystal structure. VGCCs interact with and are
regulated by a number of signaling proteins, including G proteins, calmodulin,
syntaxin and SNAP-25. These interactions are mediated by different cytoplasmic
domains of the (1 subunit and are functionally important. We are attempting to
obtain the x-ray crystal structure of these domains and understand their
Jun, X., Zhen, X-G., and Yang, J. (2003). Localization of the gate of PIP2 activation of an inward rectifier K+ channel. Nature Neurosci. In press.
Wu, L., Bauer, C., Zhen, X-G., Xie, C., and Yang, J. (2002). Dual regulation of voltage-gated Ca2+ channels by PIP2. Nature 419, 947-952.
Lu, T., Wu, L., Xiao, J., and Yang, J. (2001). Permeant ion-dependent changes in gating of Kir2.1 inward rectifier potassium channels. J. Gen. Physiol. 118, 509-521.
Lu, T., Ting, A.Y., Mainland, J., Jan, L.Y., Schultz, P.G., and Yang, J. (2001). Probing ion permeation and gating in a K+ channel with backbone mutations in the selectivity filter. Nature Neurosci. 4, 239-246.
Lu, T., Zhu, Y-G., and Yang, J. (1999). Cytoplasmic amino and carboxyl domains form a wide internal vestibule in an inwardly rectifying K+ channel. Proc. Natl. Acad. Sci. 96, 9926-9931.
Lu, T., Zhang, X-M., Nguyen, B., and Yang,
J. (1999). Architecture of a K+
channel inner pore revealed by stoichiometric covalent modification. Neuron 22, 571-580.
|W3004||Cellular and Molecular Neurobiology|