Fig. 1

The structure and functions of ITGB1. A The α- and β-subunits of the integrin family have 18 and 8 different isoforms, respectively, which are combined with each other to produce 24 heterodimers. The first eight combinations (αvβ1, αvβ3, αvβ5, αvβ6, αvβ8, αIIIbβ3, α5β1, and α8β1) all recognize the amino acid binding pattern RGD in their endogenous ligands and are referred to as the RGD binding family. The second is a combination of integrins (α4β1, α4β7, α9β7, αEβ7, αLβ2, αDβ2, αMβ2, and αXβ2) that can identify the short peptide sequence Leu-Asp-Val and are expressed on leukocytes. In addition, a third combination (α1β1, α2β1, α3β1, α6β1, α7β1, α10β1, α11β1, α6β4) can bind to collagen or laminin. B Half of the 18 α-subunits (α1, α2, α10, α11, αD, αL, αM, αX, and αE subunits) have an additional 200 aa of I-domain in the β-propeller domain. The I-like domain is a metal ion-dependent adhesion site (MIDAS). β-subunits usually include a PSI domain, a hybrid domain with an I-like domain (βI), an integrated I-EGF domain, and a β-tail domain. C Integrin activation can be divided into three stages: in the first stage, the extracellular segment of integrins is curved and the cytoplasmic tails of the α and β subunits are closed. In the second stage, the TM and extracellular structural domains of the β integrin are forced to unfold upon binding to the adaptor proteins Talin and/or Kindlin, an integrin-binding cofactor. This creates an accessible ligand-binding pocket (poor affinity). In the third stage, when the integrin contacts the ECM, its extracellular segment straightens, while the intracellular segment separates further in the tail. This conformational change helps to regulate the correlation between receptors, cytoskeletal proteins and signal transducers (with high affinity)