Structural Insights into Allosteric Modulation of NMDA Receptors Through the Amino-Terminal Domain

Majority of fast excitatory synaptic transmission in the mammalian brain is mediated by a class of molecules called ionotropic glutamate receptors, which include N-methyl-D-aspartate (NMDA) receptors. NMDA receptors are hetero-tetrameric ion channels that are composed of two NR1 subunits and two NR2 (A-D) subunits or NR3 subunits. NMDA receptors play key roles in numbers of important processes including synaptic plasticity and development in normal state, whereas aberrant activity of NMDA receptors is associated with ischemic brain injury and neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. Activity of NMDA receptor is tightly controlled through multiple pathways. One such mechanism is allosteric modulation through binding of small molecules to the extracellular amino terminal domain (ATD) in a subtype specific manner, i.e. polyamines and protons bind NR1, Zn2+ binds both NR2A and NR2B, and phenylethanolamine compounds bind NR2B. To understand the molecular mechanism of the ATD-dependent allosteric modulation of NMDA receptors, we have solved the structures of NR2B ATD in the zinc-bound and -free forms. The structures reveal an overall clamshell architecture with a unique domain orientation distinct from the non-NMDA receptor ATDs and molecular determinants for the zinc binding site, ion binding sites, and the architecture of the putative phenylethanolamine binding site

Induction of expressions of HLA class I and class II antigens by interferon on human renal cell carcinoma or bladder cancer cell lines

Interferon-induced expressions of HLA class I and class II (DR, DP, DQ) antigens on human renal cell carcinoma (RCC) cell lines and bladder cancer cell lines were analyzed by flowcytometry. Class I antigen was present on all six different RCC cell lines and the expression was enhanced with IFN-γ treatment except one cell line, Caki-2. Although no RCC cell lines expressed class II antigens without IFN-γ treatment, the treatment induced the expression of DR antigen in all cell lines except Caki-2. DP antigen was induced on KPK-1 and KPK-13 with exposure to IFN-γ. On the other hand, bladder cancer cell lines studied showed surface expression of class I antigen and enhanced expression of class I antigen with IFN-γ treatment. However, IFN-γ didn't enhance the expression of class II antigens on any of those bladder cancer cell lines. The minimum concentrations of IFN-γ to increase the expression of class I and DR andtigens on both KPK-13 and ACHN were 4 IU/ml and 100 IU/ml, respectively. The incubation time with IFN-γ to get the maximal expression of class I and DR antigens on KPK-13 were 36 hr and 48 hr, respectively. Meanwhile, although the expression of class I antigen on RCC cell lines was enhanced by IFN-α, IFN-α could not give any effect in class II antigens. Our results demonstrate the obvious effect of IFN-γ to enhance the expression of not only HLA class I antigen but also class II antigens on RCC cell lines

Excitatory and inhibitory D-serine binding to the NMDA receptor

N-methyl-D-aspartate receptors (NMDARs) uniquely require binding of two different neurotransmitter agonists for synaptic transmission. D-serine and glycine bind to one subunit, GluN1, while glutamate binds to the other, GluN2. These agonists bind to the receptor's bi-lobed ligand-binding domains (LBDs), which close around the agonist during receptor activation. To better understand the unexplored mechanisms by which D-serine contributes to receptor activation, we performed multi-microsecond molecular dynamics simulations of the GluN1/GluN2A LBD dimer with free D-serine and glutamate agonists. Surprisingly, we observed D-serine binding to both GluN1 and GluN2A LBDs, suggesting that D-serine competes with glutamate for binding to GluN2A. This mechanism is confirmed by our electrophysiology experiments, which show that D-serine is indeed inhibitory at high concentrations. Although free energy calculations indicate that D-serine stabilizes the closed GluN2A LBD, its inhibitory behavior suggests that it either does not remain bound long enough or does not generate sufficient force for ion channel gating. We developed a workflow using pathway similarity analysis to identify groups of residues working together to promote binding. These conformation-dependent pathways were not significantly impacted by the presence of N-linked glycans, which act primarily by interacting with the LBD bottom lobe to stabilize the closed LBD

Current status of intestinal transplantation in children

Purpose: A clinical trial of intestinal transplantation (Itx) under tacrolimus and prednisone immunosuppression was initiated in June 1990 in children with irreversible intestinal failure and who were dependent on total parenteral nutrition (TPN). Methods: Fifty-five patients (28 girls, 27 boys) with a median age of 3.2 years (range, 0.5 to 18 years) received 58 intestinal transplants that included isolated small bowel (SB) (n = 17), liver SB (LSB) (n = 33), and multivisceral (MV) (n = 8) allografts. Nine patients also received bone marrow infusion, and there were 20 colonic allografts. Azathioprine, cyclophosphamide, or mycophenolate mofetil were used in different phases of the series. Indications for Itx included: gastroschisis (n = 14), volvulus (n = 13), necrotizing enterocolitis (n = 6), intestinal atresia (n = 8), chronic intestinal pseudoobstruction (n = 5), Hirschsprung's disease (n = 4), microvillus inclusion disease (n = 3), multiple polyposis (n = 1), and trauma (n = 1). Results: Currently, 30 patients are alive (patient survival, 55%; graft survival, 52%). Twenty-nine children with functioning grafts are living at home and off TPN, with a mean follow-up of 962 (range, 75 to 2,424) days. Immunologic complications have included liver allograft rejection (n = 18), intestinal allograft rejection (n = 52), posttransplant lymphoproliferative disease (n = 16), cytomegalovirus (n = 16) and graft-versus-host disease (n = 4). A combination of associated complications included intestinal perforation (n = 4), biliary leak (n = 3), bile duct stenosis (n = 1), intestinal leak (n = 6), dehiscence with evisceration (n = 4), hepatic artery thrombosis (n = 3), bleeding (n = 9), portal vein stenosis (n = 1), intraabdominal abscess (n = 11), and chylous ascites (n = 4). Graft loss occurred as a result of rejection (n = 8), infection (n = 12), technical complications (n = 8), and complications of TPN after graft removal (n = 3). There were four retransplants (SB, n = 1; LSB n = 3). Conclusions: Intestinal transplantation is a valid therapeutic option for patients with intestinal failure suffering complications of TPN. The complex clinical and immunologic course of these patients is reflected in a higher complication rate as well as patient and graft loss than seen after heart, liver, and kidney transplantation, although better than after lung transplantation

Development and characterization of functional antibodies targeting NMDA receptors

N-methyl-D-aspartate receptors (NMDARs) are critically involved in basic brain functions and neurodegeneration as well as tumor invasiveness. Targeting specific subtypes of NMDARs with distinct activities has been considered an effective therapeutic strategy for neurological disorders and diseases. However, complete elimination of off-target effects of small chemical compounds has been challenging and thus, there is a need to explore alternative strategies for targeting NMDAR subtypes. Here we report identification of a functional antibody that specifically targets the GluN1-GluN2B NMDAR subtype and allosterically down-regulates ion channel activity as assessed by electrophysiology. Through biochemical analysis, x-ray crystallography, single-particle electron cryomicroscopy, and molecular dynamics simulations, we show that this inhibitory antibody recognizes the amino terminal domain of the GluN2B subunit and increases the population of the non-active conformational state. The current study demonstrates that antibodies may serve as specific reagents to regulate NMDAR functions for basic research and therapeutic objectives

Urgent revascularization of liver allografts after early hepatic artery thrombosis

Between April 1993 and May 1995, 17 adult orthotopic liver transplant recipients were found to have early hepatic artery thrombosis (HAT) after a median of 7 postoperative days (mean, 11). The HAT was diagnosed in all cases by duplex ultrasound. Thrombectomy was performed with urgent revascularization (UR), using an interposition arterial graft procured from the cadaveric liver donor, and arterial patency was verified with intraoperative angiography. In seven cases, intra-arterial urokinase was administered after the thrombectomy. Fifteen (88%) of the livers remained arterialized throughout the follow-up period (median, 15 months); the remaining two patients developed recurrent HAT after 6 and 8 months. Although there was a high rate of subsequent complications, 11 (65%) of the patients are alive without retransplantation, with a mean follow-up of 17 months. Despite having a patent hepatic artery, the remaining six patients (35%) died from infectious complications that usually were present before the UR. Thus, UR effectively restored arterial inflow in 88% of the patients with early HAT. The ultimate outcome was determined mainly by the presence of intra- abdominal complications at the time of UR. In conclusion, UR, rather than retransplantation, should be considered the prime treatment option for patients who develop early posttransplant HAT

Production of Heteromeric Transmembrane Receptors with Defined Subunit Stoichiometry

Signal transduction across cell membranes often requires assembly of heteromeric receptors with defined stoichiometry. In this issue of Structure, Morales-Perez et al. (2016) present elegant methods for the expression of heteromeric nicotinic acetylcholine receptors with a defined α4β2 stoichiometry involving controlled baculovirus-mediated transduction and subunit counting by measurement of two fluorescent signals