Low-affinity integrin states have faster ligand-binding kinetics than the high-affinity state

eLife

Jing Li¹  Jiabin Yan¹  Timothy A Springer¹ 

[1] Program in Cellular and Molecular Medicine, Boston Children’s Hospital, Boston, United States;Department of Biological Chemistry and Molecular Pharmacology and Department of Pediatrics, Harvard Medical School, Boston, United States;

关键词: integrin α4β1;    integrin α5β1;    binding kinetics;    cytoskeletal force;    None;   

DOI  :  10.7554/eLife.73359

来源: eLife Sciences Publications, Ltd

【 摘 要 】

Integrin conformational ensembles contain two low-affinity states, bent-closed and extended-closed, and an active, high-affinity, extended-open state. It is widely thought that integrins must be activated before they bind ligand; however, one model holds that activation follows ligand binding. As ligand-binding kinetics are not only rate limiting for cell adhesion but also have important implications for the mechanism of activation, we measure them here for integrins α4β1 and α5β1 and show that the low-affinity states bind substantially faster than the high-affinity state. On- and off-rates are similar for integrins on cell surfaces and as ectodomain fragments. Although the extended-open conformation’s on-rate is ~20-fold slower, its off-rate is ~25,000-fold slower, resulting in a large affinity increase. The tighter ligand-binding pocket in the open state may slow its on-rate. Low-affinity integrin states not only bind ligand more rapidly, but are also more populous on the cell surface than high-affinity states. Thus, our results suggest that integrin binding to ligand may precede, rather than follow, activation by ‘inside-out signaling.’

【 授权许可】

CC BY