Modulation of agrin function by alternative splicing and Ca2+ binding.
Stetefeld J, Alexandrescu AT, Maciejewski MW, Jenny M, Rathgeb-Szabo K, Schulthess T, Landwehr R, Frank S, Ruegg MA, Kammerer RA.
Department of Biophysical Chemistry, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland. joerg.stetefeld@unibas.ch
The aggregation of acetylcholine receptors on postsynaptic membranes is a key step in neuromuscular junction development. This process depends on alternatively spliced forms of the proteoglycan agrin with "B-inserts" of 8, 11, or 19 residues in the protein's globular C-terminal domain, G3. Structures of the neural B8 and B11 forms of agrin-G3 were determined by X-ray crystallography. The structure of G3-B0, which lacks inserts, was determined by NMR. The agrin-G3 domain adopts a beta jellyroll fold. The B insert site is flanked by four loops on one edge of the beta sandwich. The loops form a surface that corresponds to a versatile interaction interface in the family of structurally related LNS proteins. NMR and X-ray data indicate that this interaction interface is flexible in agrin-G3 and that flexibility is reduced by Ca(2+) binding. The plasticity of the interaction interface could enable different splice forms of agrin to select between multiple binding partners.
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PMID: 15016366 [PubMed - indexed for MEDLINE]