module: dmel_copii_coat
title: COPII coat in Drosophila melanogaster
label: COPII coat
module_type: PROTEIN_COMPLEX
description: >-
  The COPII coat forms vesicles and tubules that export secretory cargo from
  endoplasmic reticulum exit sites to the Golgi apparatus. The small GTPase
  Sar1, activated by its ER-membrane exchange factor, inserts into the
  membrane and recruits the inner coat, a heterodimer of Sec23 and Sec24.
  Sec24 binds cargo sorting signals, and Sec23 is the GTPase-activating
  protein for Sar1. The inner coat then recruits the outer coat of Sec13 and
  Sec31, which forms a cage around the bud and stimulates Sec23 GAP activity.
  Drosophila has two Sec24 paralogs, Sec24AB and Sec24CD.
summary: >-
  Sar1, Sec23-Sec24 and Sec13-Sec31 coat that packages cargo into vesicles at
  ER exit sites for transport to the Golgi.
concepts:
  - {id: GO:0030127, label: COPII vesicle coat}
cellular_components:
  - {id: GO:0005789, label: endoplasmic reticulum membrane}
notes: >-
  Boundary. The module contains Sar1 and the inner and outer coat proteins.
  The Sar1 exchange factor (Sec12 homolog), Sec16 and the TANGO1 machinery for
  large cargo organize exit sites and are context, not parts. The two Sec24
  paralogs are modelled as alternative inner-coat variants; their cargo
  preferences in Drosophila are not fully mapped.
parts:
  - id: sar1_gtpase
    label: Sar1 GTPase
    role: coat recruitment GTPase
    genes: [Sar1]
    complex: false
    function: {id: GO:0003924, label: GTPase activity}
    processes:
      - {id: GO:0006888, label: endoplasmic reticulum to Golgi vesicle-mediated transport}
  - id: inner_coat
    label: Sec23-Sec24 inner coat
    role: cargo selection and Sar1 GTPase activation
    variant_sets:
      - id: sec24_variants
        label: Sec23 with Sec24AB or Sec24CD
        selection: ONE_OR_MORE
        variants:
          - id: sec23_sec24ab
            label: Sec23-Sec24AB inner coat
            genes: [Sec23, Sec24AB]
            unit_functions:
              Sec23: {id: GO:0005096, label: GTPase activator activity}
          - id: sec23_sec24cd
            label: Sec23-Sec24CD inner coat
            genes: [Sec23, Sec24CD]
            unit_functions:
              Sec23: {id: GO:0005096, label: GTPase activator activity}
  - id: outer_coat
    label: Sec13-Sec31 outer coat
    role: outer cage
    genes: [Sec13, Sec31]
connections:
  - source: sar1_gtpase
    target: inner_coat
    connection_type: PRECEDES
    description: GTP-bound Sar1 recruits the Sec23-Sec24 inner coat to the ER membrane.
  - source: inner_coat
    target: outer_coat
    connection_type: PRECEDES
    description: The inner coat recruits the Sec13-Sec31 outer coat.
  - source: inner_coat
    target: sar1_gtpase
    connection_type: NEGATIVELY_REGULATES
    description: Sec23 stimulates GTP hydrolysis by Sar1, driving coat turnover.