The hydrophobic contacts between the center of the βI domain and the α1/α7 helices are crucial for the low-affinity state of integrin α4 β7

Mechanically Regulated Outside-In Activation of an I-Domain-Containing Integrin

Integrins are heterodimeric transmembrane proteins that mediate cellular adhesion and bidirectional mechanotransductions through their conformational allostery. The allosteric pathway of an I-domain-containing integrin remains unclear because of its complexity and lack of effective experiments. For a typical I-domain-containing integrin α_Xβ₂, molecular dynamics simulations were employed here to investigate the conformational dynamics in the first two steps of outside-in activation, the bindings of both the external and internal ligands. Results showed that the internal ligand binding is a prerequisite to the allosteric transmission from the α- to β-subunits and the exertion of external force to integrin-ligand complex. The opening state of αI domain with downward movement and lower half unfolding of α₇-helix ensures the stable intersubunit conformational transmission through external ligand binding first and internal ligand binding later. Reverse binding order induces a, to our knowledge, novel but unstable swingout of β-subunit Hybrid domain with the retained close states of both αI and βI domains. Prebinding of external ligand greatly facilitates the following internal ligand binding and vice versa. These simulations furthered the understanding in the outside-in activation of I-domain-containing integrins from the viewpoint of internal allosteric pathways.

Structural Basis for Differences in Dynamics Induced by Leu Versus Ile Residues in the CD Loop of Kir Channels

The effect of the conserved Leu/Ile site in the CD loop on the gating dynamics of Kir channels and corresponding micro-structural mechanism remains unclear. Molecular dynamics simulations were performed to investigate the structural mechanism of chicken Kir2.2. Compared to WT, the I223L mutant channel bound to PIP₂ more strongly, was activated more rapidly, and maintained the activation state more stably after PIP₂ dissociation. Cellular electrophysiology assays of mouse Kir2.1 and human Kir2.2 indicated that, consistent with simulations, the Leu residue increased the channel responses to PIP₂ through increased binding affinity and faster activation kinetics, and the deactivation kinetics decreased upon PIP₂ inhibition. The Ile residue induced the opposite responses. This difference was attributed to the distinct hydrophobic side chain symmetries of Leu and Ile; switching between these residues caused the interaction network to redistribute and offered effective conformation transduction in the Leu systems, which had more rigid and independent subunits.

The Role of Integrin Expressing Cells in Modulating Disease Susceptibility and Progression (January 2016)

In this review we have summarized the role of gut homing molecules with a focus on the heterodimeric integrin α4β7 since the α4β7 has been shown to be important in modulating SIV transmission, disease susceptibility and progression. This review provides an overview of integrins, their structure and function to provide a general background upon which the role of the α4β7 integrin can best be understood. We also describe integrins and their cognate receptors and their potential role in modulating disease that we hope provides some food for thought on how such knowledge can be utilized for vaccine formulation.