| Biography: Dr. Nikolai Soldatov received his Ph.D. degree in bioorganic chemistry in 1981 from Shemyakin Institute of Bioorganic Chemistry of the USSR Academy of Sciences, Moscow. In 1983, while on postdoctoral training in Shemyakin Institute, he initiated research directed to the identification and isolation of skeletal muscle dihydropyridine-sensitive calcium channel. In 1986 he joined the Institute of Medical Biotechnology led by cosmonaut Prof. B. Egorov and studied the relationship between calcium channels and primary and secondary messengers of human fibroblasts proliferation and memory, learning and nootropic effects in the brain. In 1990 he joined the laboratory of Dr. G. Blobel at the Rockefeller University, New York, as a HHMI Research Associate. He cloned the first human L-type calcium channel from fibroblasts and investigated its genomic structure. Since 1993 he has worked as an Assistant at the Department of Pharmacology of the University of Bern, Switzerland. He constructed a representative panel of human calcium channel splice variants and investigated, in collaboration with Prof. H. Reuter, their pharmacological and electrophysiological properties. In 1996 he moved to Georgetown University Medical Center, Washington, D.C., where he worked as an Assistant Professor of the Department of Pharmacology. He studied mechanisms of voltage- and calcium-induced inactivation, cross-talk between calcium channel and angiotensin receptor, and the role of C-terminal tail of the channel in calcium signaling in cardiac myocytes. In July 1999 Dr. Soldatov joined NIA as an Investigator. He is an Adjunct Associate Professor at Georgetown University and a member of the Editorial Advisory Board of the Journal of Pharmacology and Experimental Therapeutics. |
| Functional Architecture and Regulation of Human L-type Ca2+ Channel: Green fluorescent protein (GFP) has become a unique tool of investigation in molecular biology because it can be genetically fused to many proteins without significantly affecting their functional properties. Spectral characteristics of the enhanced cyan (ECFP) and yellow (EYFP) variants of GFP are well suited for measurements of molecular rearrangements by fluorescence resonance energy transfer (FRET). Because FRET depends on the distance and angular orientation between the fluorescent partners, relative change of these parameters may be measured when the functional state of the Ca2+ channel (resting, open, inactivated) is stabilized by voltage clamp. This idea of differential voltage-gated FRET was successfully implemented by combining FRET microscopy with a patch clamp to study molecular dynamics of the human vascular L-type Ca2+ channel in real time and in the live cell. The Ca2+ channel a1C pore-forming subunit was genetically fused with N-terminal EYFP and C-terminal ECFP and the labeled channel was functionally expressed in COS1 cells. This revealed voltage-gated mobility of the cytoplasmic tails of the Cav1.2 channel and its essential regulatory role in intracellular signaling. Anchoring of the C-terminal tail to the plasma membrane caused an inhibition of its state-dependent mobility, channel inactivation, and CREB-mediated transcription. Release of the tail restored these functions suggesting a direct role for voltage-gated mobility of the C-terminal tail in Ca2+ signaling. Future investigation of the functional architecture of this and other ion channels using voltage-gated differential FRET microscopy of various functional parts and subunits may complement crystallographic studies by providing characterization of the dynamic molecular changes associated with distinct functional states of ion channels in live cell. |
| Molecular Determinant of the Voltage-dependent Inactivation: Currents through the Ca2+ channel inactivate by fast and slow mechanisms. We previously described the naturally occurring A752T mutation at the cytoplasmic pore region of the human channel (Soldatov, Proc Natl Acad Sci USA, 1992). This mutation prevented a large (~25%) fraction of the current from inactivation. Incorporation of similar mutations in the analogous positions of the four repeats of the a1C subunit completely inhibited both Ca2+-dependent and slow inactivation. The mechanisms of functional targeting of the outlined annular determinant of slow inactivation by C-terminal Ca2+ sensors of inactivation and regulatory b-subunit are the subjects of ongoing investigation using electrophysiology, immunochemistry, FRET, and transgenic animal models. |
| Calcium Sensors of Calcium Channel: The voltage-gated L-type Ca2+ channel is inhibited by permeating Ca2+ but not Ba2+ ions. This Ca2+-induced inactivation serves as an important feedback mechanism in Ca2+ signal transduction that generates great variety of cellular responses. The C-terminal tail of the channel is crucial for Ca2+-induced inactivation. Two C-terminal motifs, LA and K, were identified. LA serves as a Ca2+ sensor site that binds calmodulin (CaM) at low resting free Ca2+ concentration, and K as the binding site for the Ca2+-loaded CaM. A Ca2+-dependent transfer of CaM from LA to the K-motif removes CaM from the inner mouth of the pore and thus eliminates slow inactivation by facilitating the constriction of the pore. The mobile C-tail then shuttles the Ca2+/CaM complex with the K-motif to a downstream target of the Ca2+ signaling cascade, where Ca2+ is released as an activating stimulus. Apo-CaM rebinds to LA and returns to the pore region for a new cycle of Ca2+-signal transduction. This model predicts strong modulation of the Ca2+ channel open probability and the C-tail-mediated signal transduction by intracellular Ca2+ release because of the inhibition of the dissociation of Ca2+ from the complex of CaM with locus K. In addition, cross-linking by CaMLA, similar to that which occurs in the pore, might have a role in regulation by the channel C-tail of downstream targets such as ryanodine receptor. These factors might have important physiological implications for the relationship between Ca2+-induced inactivation and Ca2+signal transduction in complex systems such as cardiac muscle. |
| Recent Publications: |
- Woo SH, Soldatov NM, Morad M. Modulation of Ca2+ signalling in rat atrial myocytes: possible role of the a1C carboxyl terminal. J. Physiol. 552(Pt 2): 437-47, 2003.
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- He LP, Cleemann L, Soldatov NM, Morad M. Molecular determinants of cAMP-mediated regulation of the Na+-Ca2+ exchanger expressed in human cell lines. J. Physiol. 548(Pt 3): 677-689, 2003.
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- Soldatov NM. Ca2+ channel moving tail: link between Ca2+-induced inactivation and Ca2+ signal transduction. Trends Pharmacol. Sci. 24(4): 167-171, 2003.
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- Kobrinsky E, Schwartz E, Abernethy DR, Soldatov NM. Voltage-gated mobility of the Ca2+ channel cytoplasmic tails and its regulatory role. J. Biol. Chem. 278(7): 5021-5028, 2003.
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- Shi C, Soldatov NM. Molecular determinants of voltage-dependent slow inactivation of the Ca2+ channel. J. Biol. Chem. 277(9): 6813-6821, 2002.
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