title: A new mode of SAM domain mediated oligomerization observed in the CASKIN2 neuronal scaffolding protein.
abstract: CASKIN2 is a homolog of CASKIN1, a scaffolding protein that participates in a signaling network with CASK (calcium/calmodulin-dependent serine kinase). Despite a high level of homology between CASKIN2 and CASKIN1, CASKIN2 cannot bind CASK due to the absence of a CASK Interaction Domain and consequently, may have evolved undiscovered structural and functional distinctions.
  
  
  
  We demonstrate that the crystal structure of the Sterile Alpha Motif (SAM) domain tandem (SAM1-SAM2) oligomer from CASKIN2 is different than CASKIN1, with the minimal repeating unit being a dimer, rather than a monomer. Analytical ultracentrifugation sedimentation velocity methods revealed differences in monomer/dimer equilibria across a range of concentrations and ionic strengths for the wild type CASKIN2 SAM tandem and a structure-directed double mutant that could not oligomerize. Further distinguishing CASKIN2 from CASKIN1, EGFP-tagged SAM tandem proteins expressed in Neuro2a cells produced punctae that were distinct both in shape and size.
  
  
  
  This study illustrates a new way in which neuronal SAM domains can assemble into large macromolecular assemblies that might concentrate and amplify synaptic responses.
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.
authors.forename: Ekaterina
authors.initials: E
authors.lastname: Smirnova
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.
authors.forename: Jamie J
authors.initials: JJ
authors.lastname: Kwan
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.
authors.forename: Ryan
authors.initials: R
authors.lastname: Siu
authors.affiliation: Division of Computer, Computational Bioscience Research Center, Electrical and Mathematical Science and Engineering, King Abdullah University of Science and Technology, Thuwal, 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Xin
authors.initials: X
authors.lastname: Gao
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.|Department of Psychology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.
authors.forename: Georg
authors.initials: G
authors.lastname: Zoidl
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center at San Antonio, 7760 Floyd Curl Drive, San Antonio, TX, 78229-3900, USA.
authors.forename: Borries
authors.initials: B
authors.lastname: Demeler
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada.
authors.forename: Vivian
authors.initials: V
authors.lastname: Saridakis
authors.affiliation: Department of Biology, York University, 4700 Keele Street, Toronto, ON, M3J 1P3, Canada. logand@yorku.ca.
authors.forename: Logan W
authors.initials: LW
authors.lastname: Donaldson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D056004:Molecular Dynamics Simulation; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism; D000072417:Protein Domains; D055503:Protein Multimerization
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C499244:CASKIN2 protein, human; D009419:Nerve Tissue Proteins
keywords: Analytical ultracentrifugation; Cell signaling; Crystal structure; Neuroscience; Nuclear magnetic resonance; Protein structure; Scaffold protein