Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre, Kharghar, Navi Mumbai 410210, India.
Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai 400094, India.
Biochem J. 2019 May 21;476(10):1445-1463. doi: 10.1042/BCJ20190224.
High-temperature requirement protease A4 (HtrA4) is a secretary serine protease whose expression is up-regulated in pre-eclampsia (PE) and hence is a possible biomarker of PE. It has also been altered in cancers such as glioblastoma, breast carcinoma, and prostate cancer making it an emerging therapeutic target. Among the human HtrAs, HtrA4 is the least characterized protease pertaining to both structure and its functions. Although the members of human HtrA family share a significant structural and functional conservation, subtle structural changes have been associated with certain distinct functional requirements. Therefore, intricate dissection of HtrA4 structural and functional properties becomes imperative to understand its role in various biological and pathophysiological processes. Here, using inter-disciplinary approaches including , biochemical and biophysical studies, we have done a domain-wise dissection of HtrA4 to delineate the roles of the domains in regulating oligomerization, stability, protease activity, and specificity. Our findings distinctly demonstrate the importance of the N-terminal region in oligomerization, stability and hence the formation of a functional enzyme. structural comparison of HtrA4 with other human HtrAs, enzymology studies and cleavage assays with X-linked inhibitor of apoptosis protein (XIAP) show overall structural conservation and allosteric mode of protease activation, which suggest functional redundancy within this protease family. However, significantly lower protease activity as compared with HtrA2 indicates an additional mode of regulation of the protease activity in the cellular milieu. Overall, these studies provide first-hand information on HtrA4 and its interaction with antiapoptotic XIAP thus implicating its involvement in the apoptotic pathway.
高温需求蛋白酶 A4（HtrA4）是一种分泌丝氨酸蛋白酶，其在子痫前期（PE）中表达上调，因此可能是 PE 的生物标志物。它在神经胶质瘤、乳腺癌和前列腺癌等癌症中也发生了改变，使其成为一个新兴的治疗靶点。在人类 HtrA 中，HtrA4 是结构和功能方面研究最少的蛋白酶。尽管人类 HtrA 家族的成员具有显著的结构和功能保守性，但细微的结构变化与某些特定的功能需求有关。因此，对 HtrA4 结构和功能特性的精细剖析对于理解其在各种生物学和病理生理学过程中的作用至关重要。在这里，我们使用包括生化和生物物理研究在内的跨学科方法，对 HtrA4 进行了域分解，以阐明各结构域在调节寡聚化、稳定性、蛋白酶活性和特异性方面的作用。我们的研究结果清楚地表明，N 端区域在寡聚化、稳定性以及功能性酶的形成中起着重要作用。与其他人类 HtrA 的结构比较、凋亡抑制蛋白（XIAP）的酶学研究和切割实验表明，该蛋白酶家族具有整体结构保守性和变构的蛋白酶激活模式，这表明其具有功能冗余性。然而，与 HtrA2 相比，其蛋白酶活性显著降低，这表明在细胞环境中存在对该蛋白酶活性的额外调节模式。总的来说，这些研究为 HtrA4 及其与抗凋亡 XIAP 的相互作用提供了第一手资料，从而表明其参与了细胞凋亡途径。
