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 Phe343, 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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鉴定 SERPINB1 作为人颗粒酶 H 的生理抑制剂

颗粒酶/穿孔素途径是细胞毒性淋巴细胞清除病毒感染细胞和肿瘤细胞的主要机制。必须严格控制蛋白水解级联的激活和抑制之间的平衡以避免自身损伤。Granzyme H (GzmH) 在 NK 细胞中组成型表达并诱导靶细胞死亡；然而，如何调节 GzmH 活动仍然难以捉摸。我们较早地报道了单独的非活性 D102N-GzmH 及其与其合成底物和抑制剂复合的晶体结构，并定义了底物识别和酶激活的机制。在这项研究中，我们将 SERPINB1 鉴定为 GzmH 的有效细胞内抑制剂。在 Phe343 处的反应中心环断裂后，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。我们分别以 3.0 和 2.9 Å 分辨率测定了天然构象中活性 GzmH 和 SERPINB1（LM-DD 突变体）的晶体结构。分子模型揭示了 GzmH 中用于自杀抑制的可能构象变化。我们的发现为 SERPINB1 对人类 GzmH 的抑制机制提供了新的见解。