module: dmel_troponin_complex
title: Troponin complex in Drosophila melanogaster
label: Troponin complex
module_type: PROTEIN_COMPLEX
description: >-
  Troponin is the calcium sensor of the thin filament in striated muscle. It is a
  complex of three subunits bound to tropomyosin: troponin C binds calcium,
  troponin I inhibits actomyosin interaction at rest, and troponin T anchors the
  complex to tropomyosin. When calcium binds troponin C, the inhibition by troponin
  I is relieved and tropomyosin moves to expose myosin-binding sites on actin,
  allowing contraction. Drosophila has single genes for troponin I (wings up A,
  wupA) and troponin T (upheld, up), each producing many muscle-specific isoforms by
  alternative splicing, and five troponin C genes expressed in different muscles; in
  the indirect flight muscle TpnC4 and TpnC41C are used, with TpnC4 linked to
  stretch activation.
summary: >-
  Calcium-sensing troponin C, I and T complex of the striated muscle thin filament.
concepts:
  - {id: GO:0005861, label: troponin complex}
parts:
  - id: troponin_c
    label: Troponin C
    role: calcium-binding subunit
    description: >-
      Each troponin complex contains one troponin C; the paralog used depends on the
      muscle type.
    variant_sets:
      - id: troponin_c_variants
        label: Troponin C paralogs
        selection: EXACTLY_ONE
        variants:
          - {id: tpnc41c, label: TpnC41C, genes: [TpnC41C], function: {id: GO:0005509, label: calcium ion binding}}
          - {id: tpnc4, label: TpnC4, genes: [TpnC4], function: {id: GO:0005509, label: calcium ion binding}}
          - {id: tpnc73f, label: TpnC73F, genes: [TpnC73F], function: {id: GO:0005509, label: calcium ion binding}}
          - {id: tpnc47d, label: TpnC47D, genes: [TpnC47D], function: {id: GO:0005509, label: calcium ion binding}}
          - {id: tpnc25d, label: TpnC25D, genes: [TpnC25D], function: {id: GO:0005509, label: calcium ion binding}}
  - id: troponin_i
    label: Troponin I
    role: inhibitory subunit
    genes: [wupA]
    processes:
      - {id: GO:0006942, label: regulation of striated muscle contraction}
  - id: troponin_t
    label: Troponin T
    role: tropomyosin-binding subunit
    genes: [up]
    processes:
      - {id: GO:0006942, label: regulation of striated muscle contraction}
connections:
  - source: troponin_c
    target: troponin_i
    connection_type: NEGATIVELY_REGULATES
    description: >-
      Calcium-bound troponin C relieves the inhibition of actomyosin interaction by
      troponin I.
notes: >-
  Tropomyosins (Tm1, Tm2) and actin are thin filament context and not parts. TpnC
  paralogs are modelled as an EXACTLY_ONE choice per complex; the muscle-specific
  expression pattern of TpnC25D and TpnC47D is not described here.
group: TPN-C