{"id":724,"date":"2024-11-27T02:40:56","date_gmt":"2024-11-27T02:40:56","guid":{"rendered":"http:\/\/wmtc2006.com\/?p=724"},"modified":"2024-11-27T02:40:56","modified_gmt":"2024-11-27T02:40:56","slug":"5g-i-unlabeled-fab-107-almost-abolished-binding-of-mab-24-to-the-native-agonist-preactivated-integrin","status":"publish","type":"post","link":"https:\/\/wmtc2006.com\/?p=724","title":{"rendered":"\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin"},"content":{"rendered":"<p>\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin. DISCUSSION The key finding in this report is that the function-blocking mAb 107 binds the MIDAS face of CD11bA in a manner similar to that of physiologic ligands and current ligand-mimetic antagonists but with two notable differences: (a) the mAb-derived GSK-2193874 ligand Asp107 stabilizes Ca2+ instead of Mg2+ at MIDAS, by binding to the metal ion bidentately instead of the usual monodentate binding mode seen with Mg2+\/ligand binding, and (b) ligation of MIDAS by the mAb did not elicit the conformational changes in CD11bA or in the holoreceptor that normally lead to cell adhesion. Of the two divalent cations Mg2+ and Ca2+ that are abundant in peripheral blood, the octahedral environment at MIDAS is ideally suited for binding Mg2+ (43). from several integrins in complex with ligands yielded an open conformation (12C14), where a ligand Asp\/Glu sidechain binds the MIDAS Mg2+ (or Mn2+) ion monodentately, completing the octahedral coordination sphere around the metal, and allowing the large conformational switch in the domain. Crystal structure of Ile316\/Gly CD11bA in complex with Fab 107 (Fig. 4A, Table 1) differs from the previously determined open structure of this domain (12) in two key features: each of the four CD11bA molecules in the asymmetric unit adopts the low-affinity conformation (Fig. 4B), and a Ca2+ ion is again found at MIDAS, bound GSK-2193874 bidentately by the ligand Asp107. The conformationally active 1 and 7 helices (Fig. 1A) in both low- and high-affinity CD11bA\/Fab107 complexes make discontinuous crystal contacts with symmetry-related molecules (combined respective interface areas of 444?2 and 468?2). It is unlikely that such contacts prevent the switch into the open conformation upon ligation of MIDAS by the ligand Asp107, since the CD11bA\/107 Fab complexes have been obtained by co-crystallization. Open in a separate window Figure 4 Crystal structure of Fab 107 in complex with high-affinity CD11bA and comparison with structures of closed and open CD11bA forms(A) Ribbon representation of high-affinity CD11bA\/Fab107 complex. D107 coordinates a MIDAS Ca2+ (cyan sphere) bidentately, but the high-affinity CD11bA assumes the low-affinity (closed) conformation. Orientation is as shown in Fig. 2A. The observed unraveling of the lower segment of the 7 helix (arrow) is caused by the helix-breaking I316\/G activating mutation. (B) Superposed crystal structures of low-and high-affinity CD11bA complexed with Fab 107, colored in cyan and magenta, respectively. Orientation is similar to (A). (C) Major interacting residues on the MIDAS face (shown as stick models) from Fab107\/low-affinity CD11bA (colored white), superposed on structure of closed CD11bA alone (1.jlm.pdb)(colored orange) and on that of open CD11bA alone (1ido.pdb)(colored gray). The MIDAS ion is colored in the respective color of each domain. MIDAS loops 1C3 GSK-2193874 (L1C3) are labeled. <a href=\"https:\/\/www.adooq.com\/gsk-2193874.html\">GSK-2193874<\/a> Orientation is the same as in Fig. 3A. Hydrogen- and metal ion bonds are represented with dashed red lines. See text for details. Our published kinetic studies revealed a ~7-fold lower affinity of mAb 107 to the open vs. closed CD11bA conformation (30). This difference may now be explained by the present structures: Should Fab 107 have approached open CD11bA, Ser144 from MIDAS loop 1 would likely clash with the ligand Asp107, and the sidechain of Glu244 (from MIDAS loops 3) would have to be sandwiched between Ser33 and Tyr31 of Fab 107 VL1 loop (Fig. 4C), which is energetically unfavorable. Effects of mAb 107 binding on conformational changes in the holoreceptor The effect of mAb107 binding on conformational switching of the domain in the context of the <a href=\"http:\/\/www.ncbi.nlm.nih.gov\/entrez\/query.fcgi?db=gene&#038;cmd=Retrieve&#038;dopt=full_report&#038;list_uids=1436\">CSF1R<\/a> full-length cellular integrin was next examined. We used binding of mAb 24 as the reporter of the conformational switch from the low- to high-affinity state in the A-domain (36, 37). Binding of Fab 107 to recombinant WT (low-affinity) CD11b\/CD18, stably expressed on K562 cells, in buffer containing physiologic concentrations of Ca2+ and Mg2+ (1 mM each), failed to switch the integrin to the high-affinity conformation; instead baseline binding of mAb 24 to the integrin was reduced significantly (Fig. 5A-C). Thus binding of mAb 107 to WT CD11bA MIDAS in the full-length integrin does not elicit the agonist-like activities observed upon binding of peptide- or nonpeptide small GSK-2193874 molecule ligand-mimetics to integrins (4). Open in a separate window Figure 5 Effect of Fab 107 on binding of the activation reporter mAb 24 to full-length CD11b\/CD18(A) Histograms (mean SD, n=3 independent experiments, each in triplicate) showing effect of absence and presence of unlabeled Fab 107 on binding of mAb 24 to the recombinant WT (low-affinity) integrin stably expressed on K562 cells. mAb 24 binding was expressed as a percentage of binding of the heterodimer-specific mAb IB4. The 45% drop in mAb.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin. DISCUSSION The key finding in this report is that the [&#8230;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[38],"tags":[],"class_list":["post-724","post","type-post","status-publish","format-standard","hentry","category-herg-channels"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin - Discovery and characterization of Histamine-2 Receptor Antagonists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/wmtc2006.com\/?p=724\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin - Discovery and characterization of Histamine-2 Receptor Antagonists\" \/>\n<meta property=\"og:description\" content=\"\ufeff5G-I, unlabeled Fab 107 almost abolished binding of mAb 24 to the native agonist-preactivated integrin. 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