title: Crystal structure of the agrin-responsive immunoglobulin-like domains 1 and 2 of the receptor tyrosine kinase MuSK.
abstract: Muscle-specific kinase (MuSK) is a receptor tyrosine kinase expressed exclusively in skeletal muscle, where it is required for formation of the neuromuscular junction. MuSK is activated by agrin, a neuron-derived heparan sulfate proteoglycan. Here, we report the crystal structure of the agrin-responsive first and second immunoglobulin-like domains (Ig1 and Ig2) of the MuSK ectodomain at 2.2 A resolution. The structure reveals that MuSK Ig1 and Ig2 are Ig-like domains of the I-set subfamily, which are configured in a linear, semi-rigid arrangement. In addition to the canonical internal disulfide bridge, Ig1 contains a second, solvent-exposed disulfide bridge, which our biochemical data indicate is critical for proper folding of Ig1 and processing of MuSK. Two Ig1-2 molecules form a non-crystallographic dimer that is mediated by a unique hydrophobic patch on the surface of Ig1. Biochemical analyses of MuSK mutants introduced into MuSK(-/-) myotubes demonstrate that residues in this hydrophobic patch are critical for agrin-induced MuSK activation.
authors.affiliation: Structural Biology Program, Skirball Institute of Biomolecular Medicine and Department of Pharmacology, New York University School of Medicine, New York, NY 10016, USA.
authors.forename: Amy L
authors.initials: AL
authors.lastname: Stiegler
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Burden
authors.forename: Stevan R
authors.initials: SR
authors.lastname: Hubbard
mesh_terms: D018171:Agrin / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D007136:Immunoglobulins / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry* / Q000235:genetics; D011950:Receptors, Cholinergic / Q000737:chemistry* / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics
chemical_list: D018171:Agrin; D007136:Immunoglobulins; D011950:Receptors, Cholinergic; D011994:Recombinant Proteins; C475048:MuSK protein, rat; D020794:Receptor Protein-Tyrosine Kinases