Divalent cations and ligands induce conformational changes that are highly divergent among beta1 integrins

Area of Science:

• Cell biology
• Molecular and structural biology
• Immunology

Background:

• Beta1 integrins are crucial cell surface receptors involved in cell adhesion and migration.
• Conformational changes in integrins regulate their ligand-binding activity.
• Understanding integrin regulation is key to deciphering cellular processes and disease mechanisms.

Purpose of the Study:

• To investigate and compare the conformational regulation of different beta1 integrin subtypes.
• To assess the utility of specific monoclonal antibodies (mAbs) as reporters of integrin activation.
• To elucidate the role of calcium and specific amino acid residues in alpha4beta1 integrin function.

Main Methods:

• Stimulation of various alpha/beta1 integrin pairs with manganese (Mn2+) and soluble ligands.
• Detection of conformational changes using beta1-specific mAbs (9EG7 and 15/7).
• Analysis of integrin responses upon calcium chelation (EGTA/EDTA) and site-directed mutagenesis (alpha4 D698E).

Main Results:

• Significant differences in 9EG7 epitope induction were observed among beta1 integrins upon Mn2+ or ligand stimulation, indicating varying conformational flexibilities.
• Alpha4beta1 integrin exhibited an atypical response to calcium, with calcium supporting constitutive 9EG7 epitope expression, unlike other beta1 integrins.
• A D698E mutation in alpha4 abrogated this constitutive 9EG7 expression, highlighting Asp-698's role in alpha4beta1 calcium sensitivity.

Conclusions:

• Monoclonal antibodies 9EG7 and 15/7 have limited diagnostic value for assessing beta1 integrin activation status.
• Beta1 integrins display distinct conformational flexibilities, with alpha4beta1 > alpha5beta1 > alpha2beta1 > alpha6beta1 > alpha3beta1.
• Alpha4beta1 integrin possesses a unique calcium-dependent regulatory mechanism involving Asp-698, suggesting differential inside-out signaling pathways among beta1 integrins.