Mechanisms of BMP Receptor Kinase Dysregulation in Skeletal Dysplasias

描述(由申请人提供)： 项目概述最近发现，人类四种骨形态发生蛋白(BMP)受体(ACVR1、ALK2)中的一个(617G&GT；A；Arg206His)突变与人类已知的最严重的继发性(异位)骨形成障碍有关。由于这种与组氨酸相同的替代，所有具有经典FOP(进展性骨化性纤维发育不良)特征的儿童最终会被第二个异位骨骼包裹，并阻止他们的行动。由于受体超家族(转化生长因子-2，转化生长因子-2)的细胞质结构域具有高度的同源性，先前确定的转化生长因子-2 I型受体(T2RI)激动域与抑制蛋白FKBP12和ATP类似的小分子抑制剂的复合体的晶体结构导致了可靠的基于结构的同源模型，用于解释FOP中BMP受体激酶功能改变的结构基础。在这种情况下，Arg206似乎与Asp269形成了高度保守的离子对，位于富含甘氨酸-丝氨酸(GS)的调节区，毗邻抑制蛋白(FKBP12)结合界面。由于组氨酸质子酸和去质子酸的侧链咪唑在生理pH范围内，His-Asp离子对在健康和疾病中发挥着独特的作用，充当pH敏感的开关，通过血红蛋白结合和释放O2和CO2，并在P53肿瘤抑制基因的pH敏感分子缺陷中发挥作用，这种缺陷与巴西一种罕见的遗传性疾病有关。因此，被组氨酸取代，并且只被组氨酸取代，预计会在蛋白质骨架中诱导对pH敏感的构象变化，导致在缺氧的炎症条件下受体的配体无关的激活，这被认为是引发爆炸性骨生长或软组织损伤引起的“突发事件”的潜在触发因素。我们将：(1)通过与BMP激酶和FKBP12的体外相互作用分析，通过表面等离子体共振(SPR，Biacore)分析来验证这一假想的pH依赖的自抑制丧失机制，以及(2)确定野生型和Arg206His BMP激酶在生理和低氧pH下的晶体结构，以准确确定突变是如何扰乱酶的三维结构的。这些结构将允许通过合理设计最近确定的抑制物(多索吗啡；一种吡唑并嘧啶三磷酸腺苷的竞争者)作为针对突变激酶的治疗药物来进行优化，以阻止FOP中骨骼外骨骼的积累，以及前列腺癌的骨转移，前列腺癌是男性最常见的恶性肿瘤，通常由BMP受体激酶的刺激引起。

DESCRIPTION (provided by applicant): Project Summary An single mutation (617G>A; Arg206His) within the kinase domain of just one of four human bone morphogenetic protein (BMP) receptors (ACVR1, ALK2) has recently been linked to the most catastrophic disorder of secondary (heterotopic) bone formation known to mankind. As a result of this identical substitution with histidine, all children presenting with features of classic FOP (Fibrodysplasia Ossificans Progressiva) eventually become encased in, and their movement blocked by, a second heterotopic skeleton. Because the cytoplasmic domains of the superfamily (TGF-2, transforming growth factor-2) of receptors are highly homologous, previously determined crystal structures of the TGF-2 type I receptor (T2RI) kinase domain in complex with the inhibitory protein FKBP12 and an ATP-analog small molecule inhibitor have lead to reliable structure-based homology models for interpreting the structural basis of altered BMP receptor kinase function in FOP. In this context, Arg206 appears to form a highly conserved ion pair with Asp269, situated in the glycine-serine rich (GS) regulatory region adjacent to the inhibitory protein (FKBP12) binding interface. Because the sidechain imidazole of histidine protonates and deprotonates within the physiological pH range, His-Asp ion pairs play unique roles in health and disease, acting as pH-sensitive switches for binding and release of O2 and CO2 by hemoglobin, and in a pH-sensitive molecular defect in the p53 tumor suppressor linked to a rare genetic disorder afflicting children in Brazil. Thus substitution with histidine, and only histidine, is predicted to induce a pH-sensitive conformational change in the protein backbone that leads to ligand-independent activation of the receptor under the hypoxic conditions of inflammation, postulated as an underlying trigger of episodes of explosive bone growth or "flare-ups" resulting from injuries to soft tissues. We will: (1) test this hypothetical pH-dependent mechanism of loss of autoinhibition by in vitro interaction analyses with the BMP kinase and FKBP12 by Surface Plasmon Resonance (SPR, BIAcore) assays, and (2) determine the crystal structures of the wildtype and Arg206His BMP kinases at physiological and hypoxic pH to identify precisely how the mutation perturbs the three- dimensional structure of the enzyme. These resulting structures will allow for optimization by rational design of a recently identified inhibitor (Dorsomorphin; a pyrrazolopyrimidine ATP-competitor) as a therapeutic drug targeted at the mutant kinase to block accumulation of extraskeletal bone in FOP, as well as the skeletal metastases of prostate cancer, the most common malignancy in men often resulting from stimulation of BMP receptor kinases.