Fig. 4
From: A loop region of BAFF controls B cell survival and regulates recognition by different inhibitors
Increase and rescue of BAFF activity by cross-linking. a Model of the role of the flap of BAFF for activation of BAFFR signaling: flap–flap interactions for which residue E223 is important mediate interactions between receptor-bound BAFF 3-mers. This promotes BAFFR signaling. Flap–flap interactions for which residues E223 and H218 are both required can further lead to assembly of BAFF 60-mer. b Sequence alignment of BAFF from different vertebrates in regions relevant for 3-mer to 3-mer interactions. Residue numbering is for human BAFF. Brackets link residues with symmetric interactions (e.g., K216 of one BAFF 3-mer interacts with E223 of another BAFF 3-mer and vice-versa, see also Fig. 1a), where acidic residues are shown in magenta, basic residues in blue, and the tyrosine that pairs with His218 in turquoise. Hs: Homo sapiens; Mm: Mus musculus; Md: Monodelphis domestica; Gg: Gallus gallus; Ac: Anolis carolinensis; Xt: Xenopus tropicalis; Lc: Latimeria chalumnae; Lo: Lepisosteus oculatus; Om: Oncorhynchus mykiss; Pf: Poecilia formosa; Dr: Danio rerio; Cm: Callorhinchus milii; Pm: Petromyzon marinus. c Cell viability measured in BAFFR:Fas reporter cells exposed to the indicated concentrations of FLAG-hBAFF WT or mutants in the presence of a fixed concentration of a control antibody (EctoD1) or of an anti-FLAG cross-linking antibody. The experiment was performed twice. d Same as panel c, but for FLAG-mBAFF. The experiment was performed twice. e Same as panel d, but for FLAG-mBAFF E247K in the presence of a constant concentration of a control antibody (EctoD1), of a cross-linking antibody (anti-FLAG), or of cross-linking anti-mBAFF monoclonal antibodies (5A8 and Sandy-5). The experiment was performed twice. f Cell viability of primary splenic mouse B cells cultured for 3 days in the presence of titrated amounts of FLAG-mBAFF WT or E247K, alone or in the presence of fixed amounts of control (EctoD1) or cross-linking (5A8, Sandy-5) antibodies. Each point is the mean ± SEM of technical triplicates. Experiment performed once in this format (and once with less titration points)
