title: Neurotrypsin cleaves agrin locally at the synapse.
abstract: The synaptic serine protease neurotrypsin is considered to be essential for the establishment and maintenance of cognitive brain functions, because humans lacking functional neurotrypsin suffer from severe mental retardation. Neurotrypsin cleaves agrin at two homologous sites, liberating a 90-kDa and a C-terminal 22-kDa fragment from the N-terminal moiety of agrin. Morphological analyses indicate that neurotrypsin is contained in presynaptic terminals and externalized in association with synaptic activity, while agrin is localized to the extracellular space at or in the vicinity of the synapse. Here, we present a detailed biochemical analysis of neurotrypsin-mediated agrin cleavage in the murine brain. In brain homogenates, we found that neurotrypsin exclusively cleaves glycanated variants of agrin. Studies with isolated synaptosomes obtained by subcellular fractionation from brains of wild-type and neurotrypsin-overexpressing mice revealed that neurotrypsin-dependent cleavage of agrin was concentrated at synapses, where the most heavily glycanated variants of agrin predominate. Because agrin has been shown to play an important role in the formation and the maintenance of excitatory synapses in the central nervous system, its local cleavage at the synapse implicates the neurotrypsin/agrin system in the regulation of adaptive reorganizations of the synaptic circuitry in the context of cognitive functions, such as learning and memory.
authors.affiliation: Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Stephan
authors.forename: José María
authors.initials: JM
authors.lastname: Mateos
authors.forename: Serguei V
authors.initials: SV
authors.lastname: Kozlov
authors.forename: Paolo
authors.initials: P
authors.lastname: Cinelli
authors.forename: Andreas David
authors.initials: AD
authors.lastname: Kistler
authors.forename: Stefan
authors.initials: S
authors.lastname: Hettwer
authors.forename: Thomas
authors.initials: T
authors.lastname: Rülicke
authors.forename: Peter
authors.initials: P
authors.lastname: Streit
authors.forename: Beat
authors.initials: B
authors.lastname: Kunz
authors.forename: Peter
authors.initials: P
authors.lastname: Sonderegger
mesh_terms: D018171:Agrin / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001923:Brain Chemistry; D003071:Cognition; D051379:Mice; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D011134:Polysaccharides / Q000032:analysis; D012697:Serine Endopeptidases / Q000032:analysis / Q000378:metabolism*; D013569:Synapses / Q000737:chemistry / Q000378:metabolism*
chemical_list: D018171:Agrin; C000602450:C-terminal agrin fragment; D010446:Peptide Fragments; D011134:Polysaccharides; D012697:Serine Endopeptidases; C108493:neurotrypsin