Article

A Vast Repertoire of Dscam Binding Specificities Arises from Modular Interactions of Variable Ig Domains

Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095-1662, USA.
Cell (Impact Factor: 32.24). 09/2007; 130(6):1134-45. DOI: 10.1016/j.cell.2007.08.026
Source: PubMed

ABSTRACT

Dscam encodes a family of cell surface proteins required for establishing neural circuits in Drosophila. Alternative splicing of Drosophila Dscam can generate 19,008 distinct extracellular domains containing different combinations of three variable immunoglobulin domains. To test the binding properties of many Dscam isoforms, we developed a high-throughput ELISA-based binding assay. We provide evidence that 95% (>18,000) of Dscam isoforms exhibit striking isoform-specific homophilic binding. We demonstrate that each of the three variable domains binds to the same variable domain in an opposing isoform and identify the structural elements that mediate this self-binding of each domain. These studies demonstrate that self-binding domains can assemble in different combinations to generate an enormous family of homophilic binding proteins. We propose that this vast repertoire of Dscam recognition molecules is sufficient to provide each neuron with a unique identity and homotypic binding specificity, thereby allowing neuronal processes to distinguish between self and nonself.

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    • "In Drosophila and other invertebrates, self-avoidance is mediated by Dscam1 proteins—immunoglobulin superfamily members produced by alternative splicing of the DSCAM1 premRNA . This cell-autonomous and stochastic alternative splicing can theoretically produce up to 19,008 Dscam1 isoforms with distinct ectodomains, each of which have highly specific homophilic trans binding specificity (Hattori et al., 2008; Miura et al., 2013; Schmucker et al., 2000; Wojtowicz et al., 2007). Distinct cell-surface identities are generated in Drosophila by the stochastic expression of a small set of Dscam1 isoforms in each neuron (Miura et al., 2013). "
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    • "The assay works by detecting direct protein interactions with the bait protein immobilized in microtitre plates in an ELISA-style format (Bushell et al. 2008;Kerr and Wright 2012), or glass slides (Sun et al. 2012Sun et al. , 2015), that can be scaled to systematically test many thousands of interactions in parallel. Similar screening assays have been developed by others (Wojtowicz et al. 2007;Ozkan et al. 2013), but all share the two core principles: that the ectodomains are expressed in eukaryotic cells to ensure correct folding of the ectodomain region, and binding avidities are increased using multimerising tags. The application of these approaches is likely to make important contributions to elucidating the molecular basis of cellular recognition process in many different biological contexts, including mammalian gamete recognition. "
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