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The structure of Rap1 in complex with RIAM reveals specificity determinants and recruitment mechanism

Hao Zhang1, Yu-Chung Chang, Mark L Brennan

  • 1Developmental Therapeutics Program, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.

Journal of Molecular Cell Biology
|November 30, 2013
PubMed

Insights

Researchers elucidated how Rap1 GTPase specifically binds to RIAM, a key molecule in cell adhesion and tumor metastasis. This discovery reveals critical interactions, offering potential therapeutic targets for diseases involving hyperactive integrins.

Area of Science:

  • Molecular Biology
  • Structural Biology
  • Cell Biology

Background:

  • The small GTPase Rap1 activates integrins through the Rap1-interacting adaptor molecule (RIAM).
  • Understanding Rap1-RIAM interaction is crucial for targeting diseases linked to hyperactive integrins, such as tumor metastasis.
  • The precise molecular recognition mechanism between Rap1 and RIAM is not well understood.

Purpose of the Study:

  • To determine the crystal structure of the Rap1 GTPase domain bound to the RIAM RA-PH module.
  • To elucidate the molecular basis for the specific recognition and interaction between Rap1 and RIAM.
  • To understand how this interaction mediates Rap1-induced integrin activation.

Main Methods:

  • X-ray crystallography to obtain the 1.65 Å crystal structure of Rap1-GTP bound to the RIAM RA-PH module.
  • Biochemical assays to investigate the role of specific amino acid residues in Rap1-RIAM binding.
  • Cell-based assays to assess the functional consequences of disrupting the Rap1-RIAM interaction on cell adhesion and co-clustering.

Main Results:

  • The crystal structure reveals that Rap1 specifically recognizes RIAM through side-chain interactions.
  • Rap1 residue Lys31, unique among related GTPases, forms a critical salt bridge with RIAM residue Glu212, serving as the key specificity determinant.
  • Disruption of these identified interactions significantly reduces Rap1:RIAM association, co-clustering, and cell adhesion.

Conclusions:

  • The study elucidates the molecular mechanism of Rap1:RIAM interaction, highlighting Lys31 as the crucial specificity determinant.
  • This detailed structural insight explains how RIAM mediates Rap1-induced integrin activation.
  • The findings provide a structural basis for understanding the specific recruitment of effector proteins containing RA-PH modules by small GTPases.
Keywords:
RA–PHRIAMRap1crystal structureinside-out signalingintegrin signaling

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