Structural and functional studies of sTALL-1

TALL-1最近被确定为肿瘤坏死因子（TNF）配体家族的一员，其刺激B细胞增殖和免疫球蛋白的分泌。小鼠中TALL-1的过度表达导致自身免疫样表现，如成熟B细胞数量增加、类风湿因子水平升高、循环免疫复合物、抗DNA自身抗体和肾中Ig沉积。目前已鉴定出两种TALL-1受体，分别为BCMA和TACI。BCMA是TNF受体家族（TNFR）的孤儿受体，由B细胞或B细胞衍生细胞特异性表达，仅含有一个富含半胱氨酸的基序，而其他家族成员则含有3到4个基序。在3.0埃下测定了TALL-1 （sTALL-1）的功能可溶性部分的结构。sTALL-1通过新型三聚体-三聚体相互作用形成病毒样结构。这种病毒样结构也存在于溶液中。我们推测这种新结构可能是TALL-1在体内的功能单位。最后，TNF/TNFR从细胞膜外到细胞膜内的信号转导尚不清楚。本课题的目的是通过x射线晶体学阐明TALL-1和TALL-1受体的独特调控机制以及TNF/TNFR超家族成员的普遍机制。其他方法，如电子显微镜、单分子跟踪3-D显微镜重建技术、诱变、动态光散射和超离心也将被使用。提出了三个具体目标。目的1:sTALL-1的结构和功能表征。目的2：确定sTALL-1与BCMA和TACI胞外结构域相互作用的结构基础。目的3：表征TALL-1 BCMA或TACI通过细胞膜的信号转导机制。来自上述目标的所有信息可用于确定药物开发的分子靶点，以治疗由TALL-1或其他TNF家族成员功能障碍诱导的自身免疫性疾病和癌症。

TALL-1 was recently identified as a member of the tumor necrosis factor (TNF) ligand family, which stimulates B cell proliferation, and the secretion of immunoglobulins. Overexpression of TALL-1 in mice lead to autoimmune-like manifestations such as increased number of mature B cells, high levels of rheumatoid factors, circulating immune complexes, anti- DNA autoantibodies, and Ig deposition in the kidney. Two receptors for the TALL-1 have been identified, which are BCMA and TACI. BCMA, an orphan receptor of the TNF receptor family (TNFR), is specifically expressed by B cells or B cell derived cells and contains only one cysteine rich motif contrasting three to four motifs in other family members. The structure of the functional soluble portion of TALL-1 (sTALL-1) has been determined at 3.0 Angstrom units. sTALL-1 forms a virus-like structure through novel trimer-trimer interactions. This virus- like structure also exists in solution. We speculate that this novel structure could be the functional unit for TALL-1 in vivo. Finally, signal transduction from outside the cell membrane to inside the cell membrane by TNF/TNFR is not clearly understood. The goal of this proposal is to elucidate the unique regulation mechanisms of TALL-1 and TALL-1 receptors and universal mechanisms for the whole TNF/TNFR super family members through x- ray crystallography. Other approaches such as electron microscopy, single molecule tracking 3-D microscopy rebuilding techniques, mutagenisis, dynamic light scattering, and ultracentrifugation will also be used. Three specific aims are proposed. Aim 1: Structural and functional characterization of sTALL-1. Aim 2: Determining the structural basis of sTALL-1 interaction with extra cellular domains of BCMA and TACI. Aim 3: Characterizing the signal transduction mechanisms of TALL-1 BCMA or TACI through the cell membrane. All information derived from the above goal can be used to identify molecular targets for drug development against autoimmune diseases and cancer induced by TALL-1 or other TNF family member malfunctioning.