The granzyme/perforin pathway is a major mechanism for cytotoxic lymphocytes to eliminate virus-infected and tumor cells. The balance between activation and inhibition of the proteolytic cascade must be tightly controlled to avoid self damage. Granzyme H (GzmH) is constitutively expressed in NK cells and induces target cell death; however, how GzmH activity is regulated remains elusive. We reported earlier the crystal structures of inactive D102N-GzmH alone and in complex with its synthetic substrate and inhibitor, as well as defined the mechanisms of substrate recognition and enzymatic activation. In this study, we identified SERPINB1 as a potent intracellular inhibitor for GzmH. Upon cleavage of the reactive center loop at Phe(343), SERPINB1 forms an SDS-stable covalent complex with GzmH. SERPINB1 overexpression suppresses GzmH- or LAK cell-mediated cytotoxicity. We determined the crystal structures of active GzmH and SERPINB1 (LM-DD mutant) in the native conformation to 3.0- and 2.9-Å resolution, respectively. Molecular modeling reveals the possible conformational changes in GzmH for the suicide inhibition. Our findings provide new insights into the inhibitory mechanism of SERPINB1 against human GzmH.

中文翻译：

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SERPINB1作为人类颗粒酶H的生理抑制剂的鉴定。

颗粒酶/穿孔素途径是细胞毒性淋巴细胞消除病毒感染和肿瘤细胞的主要机制。必须严格控制蛋白水解级联反应的激活和抑制之间的平衡，以避免自身损坏。颗粒酶H（GzmH）在NK细胞中组成性表达，并诱导靶细胞死亡。但是，如何调节GzmH活性仍然不清楚。我们更早地报道了无活性的D102N-GzmH的晶体结构及其合成底物和抑制剂的复合物，以及底物识别和酶促活化的机制。在这项研究中，我们确定了SERPINB1是GzmH的有效细胞内抑制剂。在Phe（343）处的反应性中心环裂解后，SERPINB1与GzmH形成SDS稳定的共价复合物。SERPINB1过表达抑制GzmH或LAK细胞介导的细胞毒性。我们确定了天然构象分别为3.0-和2.9-Å分辨率的活性GzmH和SERPINB1（LM-DD突变体）的晶体结构。分子建模揭示了GzmH对自杀抑制可能的构象变化。我们的发现为SERPINB1抑制人GzmH的机制提供了新的见解。