title: Structural basis for a Munc13-1 homodimer to Munc13-1/RIM heterodimer switch.
abstract: C(2) domains are well characterized as Ca(2+)/phospholipid-binding modules, but little is known about how they mediate protein-protein interactions. In neurons, a Munc13-1 C(2)A-domain/RIM zinc-finger domain (ZF) heterodimer couples synaptic vesicle priming to presynaptic plasticity. We now show that the Munc13-1 C(2)A domain homodimerizes, and that homodimerization competes with Munc13-1/RIM heterodimerization. X-ray diffraction studies guided by nuclear magnetic resonance (NMR) experiments reveal the crystal structures of the Munc13-1 C(2)A-domain homodimer and the Munc13-1 C(2)A-domain/RIM ZF heterodimer at 1.44 A and 1.78 A resolution, respectively. The C(2)A domain adopts a beta-sandwich structure with a four-stranded concave side that mediates homodimerization, leading to the formation of an eight-stranded beta-barrel. In contrast, heterodimerization involves the bottom tip of the C(2)A-domain beta-sandwich and a C-terminal alpha-helical extension, which wrap around the RIM ZF domain. Our results describe the structural basis for a Munc13-1 homodimer-Munc13-1/RIM heterodimer switch that may be crucial for vesicle priming and presynaptic plasticity, uncovering at the same time an unexpected versatility of C(2) domains as protein-protein interaction modules, and illustrating the power of combining NMR spectroscopy and X-ray crystallography to study protein complexes.
authors.affiliation: Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Lu
authors.forename: Mischa
authors.initials: M
authors.lastname: Machius
authors.forename: Irina
authors.initials: I
authors.lastname: Dulubova
authors.forename: Han
authors.initials: H
authors.lastname: Dai
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Südhof
authors.forename: Diana R
authors.initials: DR
authors.lastname: Tomchick
authors.forename: Josep
authors.initials: J
authors.lastname: Rizo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray / Q000379:methods; D019281:Dimerization; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology*; D011485:Protein Binding; D011487:Protein Conformation; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D051381:Rats; D016415:Sequence Alignment; D013572:Synaptic Vesicles / Q000378:metabolism; D016335:Zinc Fingers
chemical_list: D009419:Nerve Tissue Proteins; C484282:Rims2 protein, rat; C103912:Unc13a protein, rat