A new mode of SAM domain mediated oligomerization observed in the CASKIN2 neuronal scaffolding protein

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Smirnova, Ekaterina
Kwan, Jamie J.
Siu, Ryan
Gao, Xin
Zoidl, Georg
Demeler, Borries
Saridakis, Vivian
Donaldson, Logan W.
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BioMed Central
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. Results 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. Conclusions This study illustrates a new way in which neuronal SAM domains can assemble into large macromolecular assemblies that might concentrate and amplify synaptic responses.
Open access article. Creative Commons Attribution 4.0 International License (CC BY 4.0) applies
Analytical ultracentrifugation , Cell signaling , Crystal structure , Neuroscience , Protein structure , Scaffold protein , CASKIN2 , Sterile Alpha Motif
Smirnova, E., Kwan, J. J., Siu, R., Gao, X., Zoidl, G., Demeler, B., Saridakis, V., & Donaldson, L. W. (2016). A new mode of SAM domain mediated oligomierization observed in the CASKIN2 neuronal scaffolding protein. Cell Communication and Signaling, 14(1), Article 17. https://doi.org/10.1186/s12964-016-0140-3