Autoantibodies against leucine-rich glioma inactivated 1 (LGI1) are found in patients with limbic encephalitis and focal seizures. Here, we generate patient-derived monoclonal antibodies (mAbs) against LGI1. We explore their sequences and binding characteristics, plus their pathogenic potential using transfected HEK293T cells, rodent neuronal preparations, and behavioural and electrophysiological assessments in vivo after mAb injections into the rodent hippocampus. In live cell-based assays, LGI1 epitope recognition was examined with patient sera (n = 31), CSFs (n = 11), longitudinal serum samples (n = 15), and using mAbs (n = 14) generated from peripheral B cells of two patients. All sera and 9/11 CSFs bound both the leucine-rich repeat (LRR) and the epitempin repeat (EPTP) domains of LGI1, with stable ratios of LRR:EPTP antibody levels over time. By contrast, the mAbs derived from both patients recognized either the LRR or EPTP domain. mAbs against both domain specificities showed varied binding strengths, and marked genetic heterogeneity, with high mutation frequencies. LRR-specific mAbs recognized LGI1 docked to its interaction partners, ADAM22 and ADAM23, bound to rodent brain sections, and induced internalization of the LGI1-ADAM22/23 complex in both HEK293T cells and live hippocampal neurons. By contrast, few EPTP-specific mAbs bound to rodent brain sections or ADAM22/23-docked LGI1, but all inhibited the docking of LGI1 to ADAM22/23. After intrahippocampal injection, and by contrast to the LRR-directed mAbs, the EPTP-directed mAbs showed far less avid binding to brain tissue and were consistently detected in the serum. Post-injection, both domain-specific mAbs abrogated long-term potentiation induction, and LRR-directed antibodies with higher binding strengths induced memory impairment. Taken together, two largely dichotomous populations of LGI1 mAbs with distinct domain binding characteristics exist in the affinity matured peripheral autoantigen-specific memory pools of individuals, both of which have pathogenic potential. In human autoantibody-mediated diseases, the detailed characterization of patient mAbs provides a valuable method to dissect the molecular mechanisms within polyclonal populations.

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Interleukin-2 tyrosine kinase, Itk, is an important member of the Tec family of non-receptor tyrosine kinases that play a central role in signaling through antigen receptors such as the T-cell receptor, B-cell receptor, and Fc⑀. Selective inhibition of Itk may be an important way of modulating many diseases involving heightened or inappropriate activation of the immune system. In addition to an unliganded nonphophorylated Itk catalytic kinase domain, we determined the crystal structures of the phosphorylated and nonphosphorylated kinase domain bound to staurosporine, a potent broad-spectrum kinase inhibitor. These structures are useful for the design of novel, highly potent and selective Itk inhibitors and provide insight into the influence of inhibitor binding and phosphorylation on the conformation of Itk.The Tec kinases are a family of five non-receptor tyrosine kinases that play a central role in signaling through antigenreceptors such as the T-cell receptor (TCR), 1 B-cell receptor, and Fc⑀ (1) and are essential for T-cell activation. Three members of the family, Itk, Rlk, and Tec, are activated downstream of antigen receptor engagement in T-cells and transmit signals to downstream effectors, including PLC-␥. A fourth member, Btk, appears to act independently of T-cell signaling and is essential for B-cell development and activation. Btk-deficient murine mast cells have reduced degranulation and decreased production of proinflammatory cytokines following Fc⑀RI crosslinking (2). Btk deletion in mice has a profound effect on B-cell proliferation induced by anti-IgM and inhibits immune responses to thymus-independent type II antigens (3, 4). A biological role for the final member of this family, Bmx, has not been identified.Itk is a key member of this family, and a number of factors point to the importance of this kinase in immune disease.Deletion of Itk in mice results in reduced TCR-induced proliferation and secretion of the cytokines IL-2, IL-4, IL-5, IL-10, and interferon-␥ (5-7). Also, the immunological symptoms of allergic asthma are attenuated in ItkϪ/Ϫ mice, and lung inflammation, eosinophil infiltration, and mucous production are drastically reduced in response to challenge with the allergen OVA (8). Furthermore, the Itk gene is reported to be more highly expressed in peripheral blood T-cells from patients with moderate or severe atopic dermatitis than in controls or patients with mild atopic dermatitis (9).In certain cell types, the role of Itk may be intricately linked with other members of the family. For example, in mast cells, Btk and Itk are both expressed and activated by Fc⑀RI crosslinking (10). Splenocytes from RlkϪ/Ϫ mice secrete half the IL-2 produced by wild type animals in response to TCR engagement (5), whereas the combined deletion of Itk and Rlk in mice leads to a profound inhibition of TCR-induced responses, including proliferation and production of the cytokines IL-2, IL-4, IL-5, and interferon-␥ (5, 7). Furthermore, intracellular signaling following TCR engagement is affected in Itk...

MurG is an essential bacterial glycosyltransferase enzyme in Pseudomonas aeruginosa performing one of the key membrane steps of peptidoglycan synthesis catalyzing the transfer of N-acetyl glucosamine (GlcNAc) from its donor substrate, UDP-GlcNAc, to the acceptor substrate Lipid I. We have solved the crystal structure of the complex between Pseudomonas aeruginosa MurG and UDP-GlcNAc and compared it with the previously solved complex from E. coli. The structure reveals a large-scale conformational change in the relative orientations of the N- and C-terminal domains, which has the effect of widening the cofactor binding site and displacing the UDP-GlcNAc donor. These results suggest new opportunities to design potent inhibitors of peptidoglycan biosynthesis.

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