Doc2b serves as a scaffolding platform for concurrent binding of multiple Munc18 isoforms in pancreatic islet β-cells

Latha Ramalingam, Jingping Lu, Andy Hudmon, Debbie C. Thurmond

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Biphasic glucose-stimulated insulin secretion (GSIS) from pancreatic β-cells involves soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor (SNARE) proteinregulated exocytosis. SNARE complex assembly further requires the regulatory proteinsMunc18c,Munc18-1 and Doc2b. Munc18-1 and Munc18c are required for first-and second-phase GSIS respectively. These distinct Munc18-1 and Munc18c roles are related to their transient high-affinity binding with their cognate target (t-)SNAREs, Syntaxin 1A and Syntaxin 4 respectively. Doc2b is essential for both phases ofGSIS, yet the molecular basis for this remains unresolved. Because Doc2b binds to Munc18-1 and Munc18c via its distinct C2A and C2B domains respectively, we hypothesized that Doc2b may provide a plasma membranelocalized scaffold/platform for transient docking of theseMunc18 isoforms during GSIS. Towards this, macromolecular complexes composed of Munc18c, Doc2b and Munc18-1 were detected in β-cells. In vitro interaction assays indicated that Doc2b is required to bridge the interaction between Munc18c andMunc18-1 in the macromolecular complex; Munc18c and Munc18-1 failed to associate in the absence of Doc2b. Competitionbased GST-Doc2b interaction assays revealed that Doc2b could simultaneously bind both Munc18-1 and Munc18c. Hence these data support a working model wherein Doc2b functions as a docking platform/scaffold for transient interactions with the multiple Munc18 isoforms operative in insulin release, promoting SNARE assembly.

Original languageEnglish (US)
Pages (from-to)251-258
Number of pages8
JournalBiochemical Journal
Volume464
Issue number2
DOIs
StatePublished - Dec 1 2014

Keywords

  • Doc2b
  • Insulin exocytosis
  • Islet β-cell
  • Munc18-1
  • Munc18c
  • Soluble N-ethylmaleimide-sensitive fusion proteinattachment protein receptor (SNARE) protein

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology
  • Medicine(all)

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