Integrin αvβ8Adopts a High Affinity State for Soluble Ligands Under Physiological Conditions.
It has been proposed that integrins adopt a low affinity conformation under physiological conditions. Integrin can either be activated through cytoplasm or by binding of cations such as Mn2+to the head domain. The cytoplasmic activation pathway, that is, inside-out signaling has been regarded as the physiological pathway for integrin activation. Integrin β8is important for neuron vascular development. However, due to the highly divergent cytoplasmic domain, this integrin probably does not rely on inside-out signaling for affinity regulation. We therefore hypothesized that the β8integrin uniquely assumes a constitutively high affinity state under physiological conditions. We discovered that β8indeed exhibited high binding to soluble vitronectin in the presence of Ca2+and the ligand binding could not be further enhanced by addition of Mn2+. The lower ectodomain stalk of the integrin, which is comprised by the integrin epidermal growth factor-like (I-EGF) domains and βTD domain, is critical for this high affinity conformation. In addition, we found that unlike other integrins, Mg2+at low concentration inhibited β8ligand binding. Mutagenesis studies indicated that β8integrin possesses a unique cation binding site which might contribute to the ligand binding affinity. Our study showed that both the β8lower ectodomain stalk and the head domain play an important role in its high affinity state under physiological conditions. J. Cell. Biochem. 118: 2044-2052, 2017. © 2016 Wiley Periodicals, Inc.
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana.
Ping
P
Hu
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana.
Bing-Hao
BH
Luo
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002413:Cations, Divalent; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D039482:Integrin alpha5 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D039641:Integrin beta Chains / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D008274:Magnesium / Q000737:chemistry / Q000378:metabolism; D008345:Manganese / Q000737:chemistry / Q000378:metabolism; D009154:Mutation; D011485:Protein Binding; D000072417:Protein Domains; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012995:Solubility; D012996:Solutions; D019096:Vitronectin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D002413:Cations, Divalent; D039482:Integrin alpha5; D039641:Integrin beta Chains; D008024:Ligands; D011993:Recombinant Fusion Proteins; D012996:Solutions; D019096:Vitronectin; C094865:integrin beta8; D008345:Manganese; D008274:Magnesium; D002118:Calcium
HIGH AFFINITY CONFORMATION; INTEGRIN; METAL ION BINDING; SIGNALING; SITE AFFINITY REGULATION