Apo and InsP3-bound crystal structures of the ligand-binding domain of an InsP3 receptor

Department of Physiology, Howard Hughes Medical Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Nature Structural & Molecular Biology (Impact Factor: 13.31). 09/2011; 18(10):1172-4. DOI: 10.1038/nsmb.2112
Source: PubMed

ABSTRACT We report the crystal structures of the ligand-binding domain (LBD) of a rat inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) in its apo and InsP3-bound conformations. Comparison of these two conformations reveals that LBD's first β-trefoil fold (β-TF1) and armadillo repeat fold (ARF) move together as a unit relative to its second β-trefoil fold (β-TF2). Whereas apo-LBD may spontaneously transition between gating conformations, InsP3 binding shifts this equilibrium towards the active state.

  • Source
    • "and B) [15] [16]. Other evidence for interactions between the ligand-binding domains and IP 3 -induced conformational changes comes from NMR and small-angle X-ray scattering studies performed when these domains are expressed as independent entities [55]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The ability of cells to maintain low levels of Ca(2+) under resting conditions and to create rapid and transient increases in Ca(2+) upon stimulation is a fundamental property of cellular Ca(2+) signaling mechanism. An increase of cytosolic Ca(2+) level in response to diverse stimuli is largely accounted for by the inositol 1,4,5-trisphosphate receptor (IP3R) present in the endoplasmic reticulum membranes of virtually all eukaryotic cells. Extensive information is currently available on the function of IP3Rs and their interaction with modulators. Very little, however, is known about their molecular architecture and therefore most critical issues surrounding gating of IP3R channels are still ambiguous, including the central question of how opening of the IP3R pore is initiated by IP3 and Ca(2+). Membrane proteins such as IP3R channels have proven to be exceptionally difficult targets for structural analysis due to their large size, their location in the membrane environment, and their dynamic nature. To date, a 3D structure of complete IP3R channel is determined by single-particle cryo-EM at intermediate resolution, and the best crystal structures of IP3R are limited to a soluble portion of the cytoplasmic region representing ∼15% of the entire channel protein. Together these efforts provide the important structural information for this class of ion channels and serve as the basis for further studies aiming at understanding of the IP3R function.
    Cell Calcium 09/2014; 56(3). DOI:10.1016/j.ceca.2014.08.002 · 4.21 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Although adenophostin A (AdA), the most potent agonist of d-myo-inositol 1,4,5-trisphosphate receptors (IP(3)R), is thought to mimic IP(3), the relative roles of the different phosphate groups and the adenosine motif have not been established. We synthesized all three possible bisphosphate analogues of AdA and glucose 3,4-bisphosphate (7, AdA lacking the 2'-AMP). 2'-Dephospho-AdA (6) was prepared via a novel regioselective dephosphorylation strategy. Assessment of the abilities of these bisphosphates to stimulate intracellular Ca(2+) release using recombinant rat type 1 IP(3)R (IP(3)R1) revealed that 6, a mimic of Ins(4,5)P(2), is only 4-fold less potent than IP(3), while 7 is some 400-fold weaker and even 3″-dephospho-AdA (5) is measurably active, despite missing one of the vicinal bisphosphate groups normally thought to be crucial for IP(3)-like activity. Compound 6 is the most potent bisphosphate yet discovered with activity at IP(3)R. Thus, adenosine has a direct role independent of the 2'-phosphate group in contributing toward the potency of adenophostins, the vicinal bisphosphate motif is not essential for activity at the IP(3)R, as always thought, and it is possible to design potent agonists with just two of the three phosphates. A model with a possible adenine-R504 interaction supports the activity of 5 and 6 and also allows a reappraisal of the unexpected activity previously reported for the AdA regioisomer 2″-phospho-3″-dephospho-AdA 40.
    Journal of Medicinal Chemistry 02/2012; 55(4):1706-20. DOI:10.1021/jm201571p · 5.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Inositol 1,4,5-trisphosphate receptors (InsP3R) and ryanodine receptors (RyR) are tetrameric intracellular Ca2+ channels1. For each, the pore is formed by C-terminal transmembrane domains and regulated by signals detected by the large cytosolic structures. InsP3R gating is initiated by InsP3 binding to the InsP3-binding core (IBC, residues 224-604 of InsP3R1)2 and it requires the suppressor domain (SD, residues 1-223)2-8. We present structures of the N-terminal region (NT) of InsP3R1 with (3.6 Å) and without (3.0 Å) InsP3 bound. The arrangement of the three NT domains, the SD, IBC-β and IBC-α, identifies two discrete interfaces (α and β) between the IBC and SD. Similar interfaces occur between equivalent domains (A, B and C) in RyR19. The orientations of the three domains docked into a tetrameric structure of InsP3R10 and of the ABC domains in RyR9 are remarkably similar. The importance of the α-interface for activation of InsP3R and RyR is confirmed by mutagenesis and, for RyR, by disease-causing mutations9,11,12. InsP3 causes partial closure of the clam-like IBC, disrupting the β-interface and pulling the SD towards the IBC. This reorients an exposed SD loop (HS-loop) that is essential for InsP3R activation7. The loop is conserved in RyR and includes mutations associated with malignant hyperthermia and central core disease9,11,12. The HS-loop interacts with an adjacent NT, suggesting that activation re-arranges inter-subunit interactions. The A-domain of RyR functionally replaced the SD in a full-length InsP3R, and an InsP3R in which its C-terminal transmembrane region was replaced by that from RyR1 was gated by InsP3 and blocked by ryanodine. Activation mechanisms are conserved between InsP3R and RyR. Allosteric modulation of two similar domain interfaces within an N-terminal subunit re-orients the first domain (SD or A-domain), allowing it, via interactions of the second domain of an adjacent subunit (IBC-β or B-domain), to gate the pore.
    Nature 03/2012; 483(7387):108-12. DOI:10.1038/nature10751 · 42.35 Impact Factor
Show more