TY - THES A1 - Imam, Nasir T1 - Molecular basis of collybistin conformational activation T1 - Molekulare Prinzipien der konformellen Aktivierung von Collybistin N2 - The nervous system relies on an orchestrated assembly of complex cellular entities called neurons, which are specifically committed to information management and transmission. Inter-neuronal communication takes place via synapses, membrane-membrane junctions which ensure efficient signal transfer. Synaptic neurotransmission involves release of presynaptic neurotransmitters and their reception by cognate receptors at postsynaptic terminals. Inhibitory neurotransmission is primarily mediated by the release of neurotransmitters GABA (γ-Aminobutyric acid) and glycine, which are precisely sensed by GABA type-A receptors (GABAARs) and glycine receptors (GlyRs), respectively. GABAAR assembly and maintenance is coordinated by various postsynaptic neuronal factors including the scaffolding protein gephyrin, the neuronal adaptor collybistin (CB) and cell adhesion proteins of the neuroligin (NL) family, specifically NL2 and NL4. At inhibitory postsynaptic specializations, gephyrin has been hypothesized to form extended structures underneath the plasma membrane, where its interaction with the receptors leads to their stabilization and impedes their lateral movement. Gephyrin mutations have been associated with various brain disorders, including autism, schizophrenia, Alzheimer’s disease, and epilepsy. Furthermore, gephyrin loss is lethal and causes mice to die within the first post-natal day. Gephyrin recruitment from intracellular deposits to postsynaptic membranes primarily relies on the adaptor protein CB. As a moonlighting protein, CB, a guanine nucleotide exchange factor (GEF), also catalyzes a nucleotide exchange reaction, thereby regenerating the GTP-bound state of the small GTPase Cdc42 from its GDP-bound form. The CB gene undergoes alternative splicing with the majority of CB splice variants featuring an N-terminal SH3 domain followed by tandem Dbl-homology (DH) and pleckstrin-homology (PH) domains. Previous studies demonstrated that the most widely expressed, SH3-domain containing splice variant (CB2SH3+) preferentially adopts a closed conformation, in which the N-terminally located SH3 domain forms intra-molecular interaction with the DH-PH domain tandem. Previous cell-based studies indicated that SH3 domain-encoding CB variants remain untargeted and colocalize with intracellular gephyrin deposits and hence require additional factors which interact with the SH3 domain, thus inducing an open or active conformation. The SH3 domain-deficient CB isoform (CB2SH3-), on the contrary, adopts an open conformation, which possess enhanced postsynaptic gephyrin-clustering and also effectively replenishes the GTP-bound small GTPase-Cdc42 from its GDP-bound state. Despite the fundamental role of CB as a neuronal adaptor protein maintaining the proper function of inhibitory GABAergic synapses, its interactions with the neuronal scaffolding protein gephyrin and other post synaptic neuronal factors remain poorly understood. Moreover, CB interaction studies with the small GTPase Cdc42 and TC10, a closely related member of Cdc42 subfamily, remains poorly characterized. Most importantly, the roles of the neuronal factors and small GTPases in CB conformational activation have not been elucidated. This PhD dissertation primarily focuses on delineating the molecular basis of the interactions between CB and postsynaptic neuronal factors. During the course of my PhD dissertation, I engineered a series of CB FRET (Förster Resonance Energy Transfer) sensors to characterize the CB interaction with its binding partners along with outlining their role in CB conformational activation. Through the aid of these CB FRET sensors, I analyzed the gephyrin-CB interaction, which, due to technical limitations remained unaddressed for more than two decades (refer Chapter 2 for more details). Subsequently, I also unraveled the molecular basis of the interactions between CB and the neuronal cell adhesion factor neuroligin 2 (refer chapter 2) and the small GTPases Cdc42 and TC10 (refer chapter 3) and describe how these binding partners induce a conformational activation of CB. In summary, this PhD dissertation provides strong evidence of a closely knit CB communication network with gephyrin, neuroligin and the small GTPase TC10, wherein CB activation from closed/inactive to open/active states is effectively triggered by these ligands. N2 - Das Nervensystem ist eine komplexe Ansammlung zellulärer Einheiten, darunter sind die Neuronen, die speziell für die Verarbeitung und Übertragung von Informationen zuständig sind. Die Kommunikation zwischen Neuronen erfolgt über Synapsen, spezialisierte Membran-Membran-Kontakte, die eine effiziente Signalübertragung gewährleisten. Die synaptische Neurotransmission umfasst die präsynaptische Freisetzung von Neurotransmitters und deren Empfang durch entsprechende Rezeptoren in den Postsynapsen. Die inhibitorische Neurotransmission wird in erster Linie durch die Freisetzung der Neurotransmitter GABA (γ-Aminobuttersäure-Typ) und Glycin vermittelt, die von GABA-Typ-A-Rezeptor (GABAAR) bzw. Glycinrezeptoren (GlyR) präzise wahrgenommen werden. Der Aufbau und die Aufrechterhaltung von GABAAR Clustern wird durch verschiedene postsynaptische neuronale Faktoren koordiniert, darunter das Gerüstprotein Gephyrin, das neuronale Adaptorprotein Collybistin (CB) und Zelladhäsionsproteine der Neuroligin (NL)-Familie, insbesondere NL2 und NL4. Es wird angenommen, dass Gephyrin an hemmenden postsynaptischen Spezialisierungen ausgedehnte Strukturen unterhalb der Plasmamembran bildet, und durch Interaktion mit den Rezeptoren deren laterale Diffusion verhindert. Gephyrin-Mutationen wurden mit verschiedenen Hirnkrankheiten in Verbindung gebracht, darunter Autismus, Schizophrenie, Alzheimer und Epilepsie. Der Verlust von Gephyrin ist tödlich und führt dazu, dass Mäuse innerhalb des ersten postnatalen Tages sterben. Die Rekrutierung von Gephyrin aus intrazellulären Ablagerungen zu postsynaptischen Membranen hängt in erster Linie von CB ab. Als Moonlighting-Protein katalysiert CB, ein Guanin-Nukleotid-Austauschfaktor (GEF), auch den Nukleotidaustausch und somit die Reaktivierung der kleinen GTPase Cdc42 . Das CB-Gen wird durch alternatives Spleißen modifiziert; die meisten CB-Spleißvarianten weisen eine N-terminale SH3-Domäne auf, gefolgt von Tandem aus einer Dbl-Homologie (DH)- und einer Pleckstrin-Homologie (PH)-Domäne. Frühere Studien zeigten, dass die am häufigsten exprimierte Spleißvariante, die eine SH3-Domäne enthält (CB2SH3+), vorzugsweise eine geschlossene Konformation annimmt, bei der die N-terminal gelegene SH3-Domäne eine intra-molekulare Interaktion mit dem DH-PH- Tandem eingeht. Zellbasierte Studien zeigten, dass CB-Varianten, die für die SH3-Domäne kodieren, sich innerhalb der Zelle nicht an spezifischen Orten anreichern und stattdessen mit intrazellulären Gephyrin-Ablagerungen kolokalisieren. Zusätzliche Faktoren werden benötigt, die mit der SH3-Domäne interagieren und so eine offene oder aktive Konformation hervorrufen. Die SH3-Domänen-defiziente CB-Isoform (CB2SH3-) hingegen nimmt eine offene Konformation an, die eine verstärkte postsynaptische Gephyrin-Anhäufung aufweist und die GTP-gebundene kleine GTPase Cdc42 aus ihrem GDP-gebundenen Zustand effektiv wieder regeneriert. Trotz der grundlegenden Rolle von CB als neuronales Adaptorprotein, das die ordnungsgemäße Funktion hemmender GABAerger Synapsen aufrechterhält, ist seine Interaktion mit dem neuronalen Gerüstprotein Gephyrin und anderen post-synaptischen neuronalen Faktoren nach wie vor unzureichend verstanden. Darüber hinaus sind die Interaktionsstudien von CB mit der kleinen GTPase Cdc42 und TC10, einem eng verwandten Mitglied der Cdc42-Unterfamilie, noch immer unzureichend charakterisiert. Somit war die Frage, ob diese neuronalen Faktoren sowie die kleinen GTPasen an der CB-Konformationsaktivierung beteiligt sind. Diese Dissertation konzentriert sich in erster Linie auf die Beschreibung der molekularen Grundlagen der Interaktion von CB mit postsynaptischen neuronalen Faktoren. Im Rahmen meiner Dissertation habe ich eine Reihe von CB-FRET-Sensoren (Förster-Resonanz-Energie-Transfer) entwickelt, um die CB-Interaktion mit seinen Bindungspartnern zu charakterisieren und ihre Rolle bei der CB-Konformationsaktivierung zu beschreiben. Mit Hilfe der CB-FRET-Sensoren entschlüsselte ich das langjährige Rätsel der Gephyrin-CB-Interaktion, das aufgrund technischer Beschränkungen mehr als zwei Jahrzehnte lang ungelöst blieb (siehe Kapitel 2 für weitere Einzelheiten). In der Folge habe ich auch die molekularen Grundlagen der CB-Wechselwirkung und damit ihre konformelle Aktivierung durch den neuronalen Zelladhäsionsfaktor Neuroligin 2 (siehe Kapitel 2) und die kleinen GTPasen Cdc42 und TC10 (siehe Kapitel 3) analysiertt. Zusammengefasst liefert diese Dissertation starke Beweise für ein engmaschiges CB-Kommunikationsnetzwerk mit Gephyrin, Neuroligin und der kleinen GTPase TC10, in dem der CB-Konformationswechsel vom geschlossenen/inaktiven zum offenen/aktiven Zustand effektiv durch die Liganden ausgelöst wird. KW - Guanine nucleotide exchange factor (GEF) KW - Rho GTPasw KW - inhibitory postsynapse KW - Autoinhibition KW - conformational activation KW - collybistin KW - fluorescence resonance energy transfer (FRET) KW - gephyrin KW - neurologin-2 KW - time-correlated single photon counting (TCSPC) Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-311458 ER - TY - JOUR A1 - Imam, Nasir A1 - Choudhury, Susobhan A1 - Heinze, Katrin G. A1 - Schindelin, Hermann T1 - Differential modulation of collybistin conformational dynamics by the closely related GTPases Cdc42 and TC10 JF - Frontiers in Synaptic Neuroscience N2 - Interneuronal synaptic transmission relies on the proper spatial organization of presynaptic neurotransmitter release and its reception on the postsynaptic side by cognate neurotransmitter receptors. Neurotransmitter receptors are incorporated into and arranged within the plasma membrane with the assistance of scaffolding and adaptor proteins. At inhibitory GABAergic postsynapses, collybistin, a neuronal adaptor protein, recruits the scaffolding protein gephyrin and interacts with various neuronal factors including cell adhesion proteins of the neuroligin family, the GABAA receptor α2-subunit and the closely related small GTPases Cdc42 and TC10 (RhoQ). Most collybistin splice variants harbor an N-terminal SH3 domain and exist in an autoinhibited/closed state. Cdc42 and TC10, despite sharing 67.4% amino acid sequence identity, interact differently with collybistin. Here, we delineate the molecular basis of the collybistin conformational activation induced by TC10 with the aid of recently developed collybistin FRET sensors. Time-resolved fluorescence-based FRET measurements reveal that TC10 binds to closed/inactive collybistin leading to relief of its autoinhibition, contrary to Cdc42, which only interacts with collybistin when forced into an open state by the introduction of mutations destabilizing the closed state of collybistin. Taken together, our data describe a TC10-driven signaling mechanism in which collybistin switches from its autoinhibited closed state to an open/active state. KW - autoinhibition KW - fluorescence resonance energy transfer (FRET) KW - gephyrin KW - guanine nucleotide exchange factor (GEF) KW - inhibitory postsynapse KW - Rho GTPase Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-282816 SN - 1663-3563 VL - 14 ER - TY - JOUR A1 - Kasaragod, Vikram Babu A1 - Schindelin, Hermann T1 - Structure of Heteropentameric GABAA Receptors and Receptor-Anchoring Properties of Gephyrin JF - Frontiers in Molecular Neuroscience N2 - γ-Aminobutyric acid type A receptors (GABAARs) mediate the majority of fast synaptic inhibition in the central nervous system (CNS). GABAARs belong to the Cys-loop superfamily of pentameric ligand-gated ion channels (pLGIC) and are assembled from 19 different subunits. As dysfunctional GABAergic neurotransmission manifests itself in neurodevelopmental disorders including epilepsy and anxiety, GABAARs are key drug targets. The majority of synaptic GABAARs are anchored at the inhibitory postsynaptic membrane by the principal scaffolding protein gephyrin, which acts as the central organizer in maintaining the architecture of the inhibitory postsynaptic density (iPSD). This interaction is mediated by the long intracellular loop located in between transmembrane helices 3 and 4 (M3–M4 loop) of the receptors and a universal receptor-binding pocket residing in the C-terminal domain of gephyrin. In 2014, the crystal structure of the β3-homopentameric GABAAR provided crucial information regarding the architecture of the receptor; however, an understanding of the structure and assembly of heteropentameric receptors at the atomic level was lacking. This review article will highlight recent advances in understanding the structure of heteropentameric synaptic GABAARs and how these structures have provided fundamental insights into the assembly of these multi-subunit receptors as well as their modulation by diverse ligands including the physiological agonist GABA. We will further discuss the role of gephyrin in the anchoring of synaptic GABAARs and glycine receptors (GlyRs), which are crucial for maintaining the architecture of the iPSD. Finally, we will also summarize how anti-malarial artemisinin drugs modulate gephyrin-mediated inhibitory neurotransmission. KW - GABAA KW - gephyrin KW - diazepam KW - GABA KW - PIP2 KW - artemisinin KW - Cryo-EM KW - inhibitory neurotransmission Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-189308 SN - 1662-5099 VL - 12 ER - TY - JOUR A1 - Kasaragod, Vikram Babu A1 - Schindelin, Hermann T1 - Structure of heteropentameric GABA\(_A\) receptors and receptor-anchoring properties of gephyrin JF - Frontiers in Molecular Neuroscience N2 - γ-Aminobutyric acid type A receptors (GABA\(_A\)Rs) mediate the majority of fast synaptic inhibition in the central nervous system (CNS). GABA\(_A\)Rs belong to the Cys-loop superfamily of pentameric ligand-gated ion channels (pLGIC) and are assembled from 19 different subunits. As dysfunctional GABAergic neurotransmission manifests itself in neurodevelopmental disorders including epilepsy and anxiety, GABA\(_A\)Rs are key drug targets. The majority of synaptic GABA\(_A\)Rs are anchored at the inhibitory postsynaptic membrane by the principal scaffolding protein gephyrin, which acts as the central organizer in maintaining the architecture of the inhibitory postsynaptic density (iPSD). This interaction is mediated by the long intracellular loop located in between transmembrane helices 3 and 4 (M3–M4 loop) of the receptors and a universal receptor-binding pocket residing in the C-terminal domain of gephyrin. In 2014, the crystal structure of the β3-homopentameric GABA\(_A\)R provided crucial information regarding the architecture of the receptor; however, an understanding of the structure and assembly of heteropentameric receptors at the atomic level was lacking. This review article will highlight recent advances in understanding the structure of heteropentameric synaptic GABA\(_A\)Rs and how these structures have provided fundamental insights into the assembly of these multi-subunit receptors as well as their modulation by diverse ligands including the physiological agonist GABA. We will further discuss the role of gephyrin in the anchoring of synaptic GABA\(_A\)Rs and glycine receptors (GlyRs), which are crucial for maintaining the architecture of the iPSD. Finally, we will also summarize how anti-malarial artemisinin drugs modulate gephyrin-mediated inhibitory neurotransmission. KW - GABAA receptors KW - gephyrin KW - diazepam KW - GABA KW - PIP2 KW - artemisinin KW - Cryo-EM KW - inhibitory neurotransmission Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201886 VL - 12 IS - 191 ER - TY - JOUR A1 - Khayenko, Vladimir A1 - Maric, Hans Michael T1 - Targeting GABA\(_A\)R-associated proteins: new modulators, labels and concepts JF - Frontiers in Molecular Neuroscience N2 - γ-aminobutyric acid type A receptors (GABA\(_A\)Rs) are the major mediators of synaptic inhibition in the brain. Aberrant GABA\(_A\)R activity or regulation is observed in various neurodevelopmental disorders, neurodegenerative diseases and mental illnesses, including epilepsy, Alzheimer’s and schizophrenia. Benzodiazepines, anesthetics and other pharmaceutics targeting these receptors find broad clinical use, but their inherent lack of receptor subtype specificity causes unavoidable side effects, raising a need for new or adjuvant medications. In this review article, we introduce a new strategy to modulate GABAeric signaling: targeting the intracellular protein interactors of GABA\(_A\)Rs. Of special interest are scaffolding, anchoring and supporting proteins that display high GABA\(_A\)R subtype specificity. Recent efforts to target gephyrin, the major intracellular integrator of GABAergic signaling, confirm that GABA\(_A\)R-associated proteins can be successfully targeted through diverse molecules, including recombinant proteins, intrabodies, peptide-based probes and small molecules. Small-molecule artemisinins and peptides derived from endogenous interactors, that specifically target the universal receptor binding site of gephyrin, acutely affect synaptic GABA\(_A\)R numbers and clustering, modifying neuronal transmission. Interference with GABA\(_A\)R trafficking provides another way to modulate inhibitory signaling. Peptides blocking the binding site of GABA\(_A\)R to AP2 increase the surface concentration of GABA\(_A\)R clusters and enhance GABAergic signaling. Engineering of gephyrin binding peptides delivered superior means to interrogate neuronal structure and function. Fluorescent peptides, designed from gephyrin binders, enable live neuronal staining and visualization of gephyrin in the post synaptic sites with submicron resolution. We anticipate that in the future, novel fluorescent probes, with improved size and binding efficiency, may find wide application in super resolution microscopy studies, enlightening the nanoscale architecture of the inhibitory synapse. Broader studies on GABA\(_A\)R accessory proteins and the identification of the exact molecular binding interfaces and affinities will advance the development of novel GABA\(_A\)R modulators and following in vivo studies will reveal their clinical potential as adjuvant or stand-alone drugs. KW - GABAA receptors KW - gephyrin KW - collybistin KW - protein-protein interaction (PPI) KW - super resolution microscopy KW - fluorescent probes KW - dimeric peptide KW - peptide inhibitor design Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201876 VL - 12 IS - 162 ER - TY - THES A1 - Pacios Michelena, Anabel T1 - Molecular insights into the complex formed by the actin cytoskeleton related protein VASP and the inhibitory postsynaptic scaffolding protein gephyrin T1 - Molekulare Einblicke in den Komplex, der durch das mit dem Aktin-Zytoskelett verwandte Protein VASP und Gephyrin, einem Gerüstprotein inhibitorischer postsynaptischer Strukturen, gebildet wird N2 - Gephyrin is a 93 kDa moonlighting protein, which is involved in the last two steps of the molybdenum cofactor (Moco) biosynthesis pathway while at the same time playing a central role in the anchoring, clustering and stabilization of glycine receptors (GlyRs) ... N2 - Gephyrin ist ein multifunktionales 93 kDa-Protein. Dieses Protein katalysiert die letzten beiden Schritte des Biosynthesewegs des Molybdän-Cofaktors (Moco). Gleichzeitig spielt es eine zentrale Rolle bei der Verankerung, Clusterbildung und Stabilisierung sowohl von Glycinrezeptoren (GlyRs) als auch von ... KW - gephyrin KW - vasp KW - Inhibitory-postsynapse KW - Actin cytoskeleton-related protein Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-213373 ER - TY - JOUR A1 - Piro, Inken A1 - Eckes, Anna-Lena A1 - Kasaragod, Vikram Babu A1 - Sommer, Claudia A1 - Harvey, Robert J. A1 - Schaefer, Natascha A1 - Villmann, Carmen T1 - Novel Functional Properties of Missense Mutations in the Glycine Receptor β Subunit in Startle Disease JF - Frontiers in Molecular Neuroscience N2 - Startle disease is a rare disorder associated with mutations in GLRA1 and GLRB, encoding glycine receptor (GlyR) α1 and β subunits, which enable fast synaptic inhibitory transmission in the spinal cord and brainstem. The GlyR β subunit is important for synaptic localization via interactions with gephyrin and contributes to agonist binding and ion channel conductance. Here, we have studied three GLRB missense mutations, Y252S, S321F, and A455P, identified in startle disease patients. For Y252S in M1 a disrupted stacking interaction with surrounding aromatic residues in M3 and M4 is suggested which is accompanied by an increased EC\(_{50}\) value. By contrast, S321F in M3 might stabilize stacking interactions with aromatic residues in M1 and M4. No significant differences in glycine potency or efficacy were observed for S321F. The A455P variant was not predicted to impact on subunit folding but surprisingly displayed increased maximal currents which were not accompanied by enhanced surface expression, suggesting that A455P is a gain-of-function mutation. All three GlyR β variants are trafficked effectively with the α1 subunit through intracellular compartments and inserted into the cellular membrane. In vivo, the GlyR β subunit is transported together with α1 and the scaffolding protein gephyrin to synaptic sites. The interaction of these proteins was studied using eGFP-gephyrin, forming cytosolic aggregates in non-neuronal cells. eGFP-gephyrin and β subunit co-expression resulted in the recruitment of both wild-type and mutant GlyR β subunits to gephyrin aggregates. However, a significantly lower number of GlyR β aggregates was observed for Y252S, while for mutants S321F and A455P, the area and the perimeter of GlyR β subunit aggregates was increased in comparison to wild-type β. Transfection of hippocampal neurons confirmed differences in GlyR-gephyrin clustering with Y252S and A455P, leading to a significant reduction in GlyR β-positive synapses. Although none of the mutations studied is directly located within the gephyrin-binding motif in the GlyR β M3-M4 loop, we suggest that structural changes within the GlyR β subunit result in differences in GlyR β-gephyrin interactions. Hence, we conclude that loss- or gain-of-function, or alterations in synaptic GlyR clustering may underlie disease pathology in startle disease patients carrying GLRB mutations. KW - glycine receptor KW - hyperekplexia KW - startle disease KW - gephyrin Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-246676 SN - 1662-5099 VL - 14 ER - TY - JOUR A1 - Tretter, Verena A1 - Mukherjee, Jayanta A1 - Maric, Hans-Michael A1 - Schindelin, Hermann A1 - Sieghart, Werner A1 - Moss, Stephen J. T1 - Gephyrin, the enigmatic organizer at GABAergic synapses JF - Frontiers in Cellular Neuroscience N2 - GABA(A) receptors are clustered at synaptic sites to achieve a high density of postsynaptic receptors opposite the input axonal terminals. This allows for an efficient propagation of GABA mediated signals, which mostly result in neuronal inhibition. A key organizer for inhibitory synaptic receptors is the 93 kDa protein gephyrin that forms oligomeric superstructures beneath the synaptic area. Gephyrin has long been known to be directly associated with glycine receptor beta subunits that mediate synaptic inhibition in the spinal cord. Recently, synaptic GABA(A) receptors have also been shown to directly interact with gephyrin and interaction sites have been identified and mapped within the intracellular loops of the GABA(A) receptor alpha 1, alpha 2, and alpha 3 subunits. Gephyrin-binding to GABA(A) receptors seems to be at least one order of magnitude weaker than to glycine receptors (GlyRs) and most probably is regulated by phosphorylation. Gephyrin not only has a structural function at synaptic sites, but also plays a crucial role in synaptic dynamics and is a platform for multiple protein-protein interactions, bringing receptors, cytoskeletal proteins and downstream signaling proteins into close spatial proximity. KW - scaffolding protein gephyryrin KW - containing GABA(A) receptors KW - GABA(A) receptors KW - inhibitory synapse KW - gamma-aminobutyric-acid KW - receptor-beta subunits KW - molybdenum cofactor biosynthesis KW - temporal-lobe epilepsy KW - cultured hippocampal-neurons KW - exchange factor collybistin KW - rat spinal-cord KW - glycine KW - gephyrin KW - receptor clustering KW - synapse formation Y1 - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-133356 VL - 6 IS - 23 ER -