FRET detection of cellular alpha4-integrin conformational activation

Area of Science:

• Biochemistry
• Cell Biology
• Biophysics

Background:

• Integrins are crucial cell adhesion receptors involved in various biological processes.
• Integrins are known to exist in different conformational and affinity states.
• The dynamic structural changes of integrins upon activation are not fully understood.

Purpose of the Study:

• To investigate the dynamic structural transformations of alpha4-integrins upon activation.
• To correlate changes in integrin structure with its binding affinity.
• To elucidate the mechanism behind integrin-mediated cell adhesion.

Main Methods:

• Utilized fluorescence resonance energy transfer (FRET) to measure distances between a peptide donor and membrane-bound acceptors on live cells.
• Generated different integrin affinity states using divalent ions (Mn2+) and chemokine receptor activation.
• Employed confocal microscopy to analyze the lateral organization of FRET components.

Main Results:

• A significant change in the distance of closest approach of alpha4-integrins was observed upon activation.
• Mn2+ activation led to an approximate 50 Å change, while chemokine activation resulted in a ~25 Å change.
• FRET efficiency changes were primarily attributed to the vertical extension of the integrin.

Conclusions:

• Integrin activation involves significant vertical extension, directly correlating with changes in binding affinity.
• This structural change provides a mechanism supporting the 'catch-bond' concept in cell adhesion.
• The findings offer insights into the molecular mechanisms governing integrin function.