| Integrin alphaLbeta2 is one of three beta2 integrin adhesion proteins. The non-covalent heterodimer of 180kD aL/CD11a and 95kD b2/CD18 integrin subunits is expressed on virtually all leukocytes. The ligand binding site of LFA-1 is in the N-terminal head region, formed by an interaction of the vWFA (I, I-like) domains from each subunit, and the aL betapropeller structure. The aL subunit contains domains termed thigh, calf-1 and calf-2, while the b2 subunit contains a PSI region and four cysteine-rich I-EGF folds. Each subunit has a transmembrane sequence and a short cytoplasmic tail connected to the cytoskeleton. Upon activation by ''inside-out signaling, clustering, or Mg2+ or Mn2+ binding to metal ion-dependent adhesion sites within the vWFA domains, the molecule unfolds from its inactive, ''closed conformation to expose ligand binding sites. Active aLb2 binds ICAM-1/CD54, ICAM-2, ICAM-3 and JAM-A. The adhesion stabilizes interactions between T cells and antigen-presenting cells, decreases the T cell activation threshold and facilitates leukocyte transendothelial migration to sites of inflammation. A constitutively active construct severely impairs immune responses, demonstrating that both activation and de-activation are important. Mutations of b2, especially in the vWFA domain, cause leukocyte adhesion deficiency (LAD-1) and susceptibility to bacterial infections. The 1088aa human aL/CD11b is 73-74% aa identical to mouse and rat, and 79-80% aa identical to bovine, porcine, ovine, goat and canine. The 678aa human b2/CD18 shares 81-83% aa sequence identity with mouse, rat, bovine, canine, goat, ovine and porcine b2 ECD. A second human aL isoform has 53 aa inserted after aa 954 in the ECD. The 678 aa human b 2/CD18 ECD shares 81-83% aa sequence identity with mouse, rat, bovine, canine, goat, ovine and porcine b2 ECD. Source: Human Integrin alpha L (Tyr26-Met1089) acidic tail, ~121.7kD, Accession P20701 Human Integrin beta2 (Gln23-Asn700) basic tail, ~79kD, Accession P05107 expressed in Chinese hamster ovary (CHO) cells. Molecular Mass: Based on N-terminal sequencing, the recombinant human Integrin aL subunit starts at Tyr 26 and has a calculated molecular mass of approximately 121.7kD. The N-terminal sequence of the b2 subunit was blocked, suggesting that the b2 subunit may start at the predicted Gln 23 and has a calculated molecular mass of approximately 79kD. As a result of glycosylation, the recombinant proteins migrate as approximately 160 and 100kD protein bands in SDS-PAGE under reducing conditions. SDS-PAGE: ~160kD and 100kD under reducing conditions. Predicted MW: 121.7kD (Integrin aL), 79kD (Integrin b2) Biological Activity: Measured by the ability of the immobilized protein to support the adhesion of CHO cells transfected with human ICAM-1. When 5x10e4 cells/well are added to Integrin aLb2-coated plates (5ug/ml, 100ul/well), 60-80% of the cells will adhere after 1 hour at 37C in the presence of 1mM MnCl2. Storage and Stability: Lyophilized and reconstituted products are stable for 12 months after receipt at -20C. Reconstitute with sterile PBS. Aliquot to avoid repeated freezing and thawing. Store at -20C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Further dilutions can be made in assay buffer. |
