General structural features that regulate integrin affinity revealed by atypical αVβ8

Area of Science:

• Molecular and Structural Biology
• Cellular Adhesion Mechanisms
• Protein Dynamics and Interactions

Background:

• Integrins are crucial cell surface receptors involved in cell adhesion and signaling.
• Integrin αVβ8 and αVβ6 activate latent transforming growth factor-betas (TGF-βs), but αVβ8 has atypical properties.
• Understanding integrin structural dynamics is key to deciphering their function in biological processes.

Purpose of the Study:

• To structurally and dynamically compare integrin αVβ8 with αVβ6.
• To elucidate the molecular mechanisms underlying the distinct ligand-binding affinities of αVβ8 and αVβ6.
• To identify key structural features that regulate integrin affinity and signaling.

Main Methods:

• Crystal structure determination of integrins.
• Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to probe protein dynamics.
• Site-directed mutagenesis and affinity measurements to assess functional impact.

Main Results:

• Integrin αVβ8 lacks a divalent cation binding site and possesses a unique β6-α7 loop conformation, facilitating high-affinity states.
• Unlike other integrins, αVβ8's ligand binding involves α1/α1' helix movements without significant β6-α7 loop reshaping or α7-helix pistoning.
• Reciprocal βI domain swaps between αVβ6 and αVβ8 demonstrated that these domains regulate affinity and coupling to the hybrid domain.

Conclusions:

• Integrin αVβ8's atypical structure allows for efficient TGF-β activation through unique conformational dynamics.
• Specific structural elements within the βI domain and its coupling to the hybrid domain are critical determinants of integrin affinity.
• These findings provide insights into integrin structure-function relationships and their roles in TGF-β signaling pathways.