Irina I. Serysheva, Ph.D.
Associate Professor, Biochemistry & Molecular Biology
National Center for Macromolecular Imaging
- Ph.D., Biochemistry, 1984, A. N. Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, Russia.
- M.Sc., Biochemistry (specialization: Molecular Virology), 1978, M. V. Lomonosov State University, Moscow, Russia.
Our research aims to understand molecular mechanisms underlying transport of molecules into and out of the cell across the surface membrane, or between different intracellular compartments through structure-functional studies of integral membrane proteins known as ion channels and the macromolecular complexes they form. Ion channels regulate many diverse biological functions that include muscle contraction, hormone secretion, gene transcription, metabolic regulation, neurotransmitter release, fertilization and apoptosis. The knowledge about the 3-D architecture of ion channels is required to understand molecular basis of the gating (opening/closing) process and how this process is controlled by a wide variety of endogenous molecules and pharmacological modifies. Another essential question in the field of ion channel studies is how do channel pores discriminate between various molecules. To answer these questions we use a combination of electron microscopy and computer reconstruction techniques in conjunction with biochemical, electrophysiological and molecular biological approaches.
Our current research efforts include several components: (a) purification of ion channels from natural sources or from high-level expression systems; (b) electron cryomicroscopy (cryo-EM) of the purified channel assemblies in the form of either individual particles or two dimensional crystals; (c) computer image processing and three dimensional reconstruction; (d) structure analysis and annotation using combination of visualization and computational tools; (e) prediction of functional roles of the identified structural domains via computational and bioinformatics approaches.
Recent focus has been on structural analysis of integral membrane Ca2+ channels that mediate ligand-gated release of Ca2+ from intracellular stores: the ryanodine-sensitive Ca2+ release channel (RyR), the primary Ca2+ channel in muscle cells, and the inositol 1,4,5-trisphosphate-sensitive Ca2+ release channel (IP3R), localized in the endoplasmic reticulum. Both channels are large homotetrameric protein complexes with a molecular mass of ~2.3 MDa for RyRs and 1.2 MDa for IP3Rs. We also pursue the structural studies of the L-type voltage-gated Ca2+ channel (~430 kDa) which is a hetero-oligomeric protein complex composed of five subunits. We propose that the skeletal type excitation-contraction coupling is be regulated through bi-directional signaling between the L-type Ca2+ channel and the RyR1/Ca2+ channel. Defects in these channel proteins cause abnormal regulation of cell Ca2+ level underlying numerous human diseases: Malignant Hyperthermia, Central Core disease, cardiac hypertrophy, heart failure, hereditary ataxias, Huntington’s disease, Alzheimer’s disease, osteoporosis, atherosclerosis and some migraines. Another avenue of our research is the TRPC channels that belong to the family of the transient receptor potential protein (TRP) channels localized in the plasma membrane. TRPC channels are nonspecific cation channels that are activated in response to G protein-coupled receptor activation and/or depletion of intracellular Ca2+ stores. Several lines of evidence support a conformational coupling model with an essential role for interaction between TRPC channels and intracellular Ca2+ release channels.
The membrane protein assemblies are among the most difficult targets for structural analysis for numerous reasons, including possible conformational heterogeneity in the sample representing a mixture of different functional states, possible structural flexibility of the channel, and poor image contrast due to the presence of detergent in the protein samples. Complex nature of ion channels hinders their structural determination by standard structural techniques such as X-ray crystallography or NMR spectroscopy, while cryo-EM is able to tackle both, large macromolecular assemblies as well as molecules in different functional states. The ultimate goal of our research is extending structural analysis of ion channels to a resolution beyond 8 Å in order to build an anatomic model of these molecular complexes at well-defined functional states.