Integrin alpha(2)I domain recognizes type I and type IV collagens by different mechanisms

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Integrins are cell surface receptors that mediate cell adhesion.
• The alpha(2)I domain of integrin alpha(2)beta(1) binds to collagen.
• A conserved helix alphaC in alpha(2)I domains is proposed to be involved in collagen binding.

Purpose of the Study:

• To investigate the role of helix alphaC in type I collagen binding by the alpha(2)I domain.
• To determine the function of charged amino acid residues near the metal ion-dependent adhesion site in collagen recognition.

Main Methods:

• Site-directed mutagenesis to delete helix alphaC and introduce point mutations in the alpha(2)I domain.
• Real-time biosensor assays to measure binding affinity to type I collagen.
• Cell spreading assays using Chinese hamster ovary cells expressing mutated alpha(2)beta(1) integrin.

Main Results:

• Deletion of helix alphaC significantly reduced the affinity of the alpha(2)I domain for type I collagen.
• Mutations in Asp(219), Asp(259), Asp(292), and Glu(299) also weakened type I collagen binding.
• Double mutations D219N/D292N in alpha(2)beta(1) integrin resulted in slower cell spreading on type I collagen but not type IV collagen.

Conclusions:

• Helix alphaC is crucial for the high-affinity binding of the alpha(2)I domain to type I collagen.
• Specific charged residues near the metal ion-dependent adhesion site contribute to type I collagen recognition.
• The alpha(2)I domain employs distinct binding mechanisms for type I and type IV collagen.