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The I domain in integrins evolved from a collagen-binding domain, enabling ligand binding and preserving function despite blocking the ancestral pocket. This molecular exaptation expanded cellular communication in vertebrates.

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Area of Science:

  • Biochemistry
  • Evolutionary Biology
  • Structural Biology

Background:

  • Integrins are cell surface receptors crucial for cell adhesion and signaling.
  • Ligand binding induces conformational changes in integrins for signal transmission.
  • The evolution of the integrin alpha (α) subunit's inserted (I) domain presented a challenge to conventional activation mechanisms.

Purpose of the Study:

  • To elucidate how the I domain in integrins preserves function despite obstructing the ancestral ligand-binding pocket.
  • To investigate the evolutionary origin and mechanism of I domain-mediated integrin activation.
  • To understand the role of the I domain in expanding cellular communication in vertebrates.

Main Methods:

  • Comparative analysis of cryo-electron microscopy structures of αEβ7 and α4β7 integrins.
  • Determination of apo and ligand-bound states for both integrin types.
  • Tracing the evolutionary history of the I domain.

Main Results:

  • The I domain intrinsically mimics an extrinsic ligand to maintain integrin activation.
  • The I domain's origin was traced to an ancestral collagen-collagen interaction domain.
  • This ancient molecular exaptation allowed for immediate integrin activation upon I domain insertion.

Conclusions:

  • The evolution of the I domain represents a key adaptation in integrin function.
  • Molecular exaptation of a collagen-binding domain facilitated integrin activation and expanded signaling.
  • These findings provide insight into the evolutionary and biochemical basis of vertebrate cellular communication.