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

作者：Ramalingam Latha; Lu Jingping; Hudmon Andy; Thurmond Debbie C^*

来源：Biochemical Journal, 2014, 464(2): 251-258.

DOI：10.1042/BJ20140845

• Doc2b
• insulin exocytosis
• islet beta-cell
• Munc18-1
• Munc 18c
• soluble N-ethylmaleimide-sensitive fusion protein-attachment
• protein receptor (SNARE) protein

Biphasic glucose-stimulated insulin secretion (GSIS) from pancreatic beta-cells involves soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor (SNARE) protein-regulated exocytosis. SNARE complex assembly further requires the regulatory proteins Munc 18c, Munc18-1 and Doc2b. Munc18-1 and Munc 18c are required for first- and second-phase GSIS respectively. These distinct Munc18-1 and Munc 18c 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 of GSIS, yet the molecular basis for this remains unresolved. Because Doc2b binds to Munc18-1 and Munc 18c via its distinct C2A and C2B domains respectively, we hypothesized that Doc2b may provide a plasma membrane-localized scaffold/platform for transient docking of these Munc 18 isoforms during GSIS. Towards this, macromolecular complexes composed of Munc 18c, Doc2b and Munc18-1 were detected in beta-cells. In vitro interaction assays indicated that Doc2b is required to bridge the interaction between Munc 18c and Munc 18-1 in the macromolecular complex; Munc 18c and Munc 18-1 failed to associate in the absence of Doc2b. Competition-based GST Doc2b interaction assays revealed that Doc2b could simultaneously bind both Munc18-1 and Munc 18c. Hence these data support a working model wherein Doc2b functions as a docking platform/scaffold for transient interactions with the multiple Munc 18 isoforms operative in insulin release, promoting SNARE assembly.

• 出版日期2014-12-1