Unique charge-dependent constraint on collagen recognition by integrin α10β1

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Collagen-binding integrins are crucial cell surface receptors that mediate cell adhesion and signaling.
• The inserted (I) domain of integrins is responsible for direct collagen recognition.
• Specific collagen motifs, like GROGER, are recognized by integrins through interactions within the I domain, often involving metal ion-dependent binding sites.

Purpose of the Study:

• To investigate the molecular basis for the weak recognition of the GROGER motif by the α10β1 integrin, a key collagen receptor on chondrocytes.
• To understand the structural determinants of integrin-collagen interactions, particularly concerning the α10β1 integrin and collagen II.

Main Methods:

• Sequence alignment of integrin I domains.
• Molecular modeling to predict structural interactions.
• Site-directed mutagenesis of key amino acid residues in integrin α10β1.
• Assessment of integrin-ligand binding affinities.

Main Results:

• The α10β1 integrin exhibits weak binding to the GROGER motif found in collagens I and III.
• A structural clash between a unique arginine residue (R215) in the α10β1 I domain and the positively-charged GROGER motif was identified.
• Replacing R215 with glutamine restored α10β1 binding to GROGER.
• Mutating equivalent residues in α1 and α2 integrin I domains impaired their GROGER binding.
• Collagen II, lacking GROGER but containing GRSGET, is also not recognized by α10β1.

Conclusions:

• The R215 residue in α10β1 is critical for its specific interaction with collagen, explaining its weak recognition of GROGER.
• These findings suggest an evolutionary mechanism to maintain accessibility of collagen II's terminal domains in cartilage.
• This accessibility may be important during processes like endochondral ossification, where α10β1 is the primary collagen receptor on chondrocytes.