Non-photochemical quenching (NPQ) plays an important role for phototrophs in decreasing photo-oxidative damage. qH is a sustained form of NPQ and depends on the plastid lipocalin (LCNP). A thylakoid membrane-anchored protein SUPPRESSOR OF QUENCHING1 (SOQ1) prevents qH formation by inhibiting LCNP. SOQ1 suppresses qH with its lumen-located thioredoxin (Trx)-like and NHL domains. Here we report structural data, genetic modification and biochemical characterization of Arabidopsis SOQ1 lumenal domains. Our results show that the Trx-like and NHL domains are associated together, with the cysteine motif located at their interface. Residue E859, required for SOQ1 function, is pivotal for maintaining the Trx–NHL association. Importantly, the C-terminal region of SOQ1 forms an independent β-stranded domain that has structural homology to the N-terminal domain of bacterial disulfide bond protein D and is essential for negative regulation of qH. Furthermore, SOQ1 is susceptible to cleavage at the loops connecting the neighbouring lumenal domains both in vitro and in vivo, which could be a regulatory process for its suppression function of qH.

非光化学猝灭 (NPQ) 在光养生物减少光氧化损伤方面起着重要作用。qH 是 NPQ 的一种持续形式，取决于质体脂质运载蛋白 (LCNP)。类囊体膜锚定蛋白 SUPPRESSOR OF QUENCHING1 (SOQ1) 通过抑制 LCNP 来防止 qH 形成。SOQ1 通过其位于内腔的硫氧还蛋白 (Trx) 样和 NHL 结构域抑制 qH。在这里，我们报告了拟南芥的结构数据、遗传修饰和生化特性SOQ1 腔域。我们的结果表明 Trx 样结构域和 NHL 结构域关联在一起，半胱氨酸基序位于它们的界面。SOQ1 功能所需的残基 E859 对于维持 Trx-NHL 关联至关重要。重要的是，SOQ1 的 C 端区域形成一个独立的 β 链结构域，该结构域与细菌二硫键蛋白 D 的 N 端结构域具有结构同源性，对于 qH 的负调节至关重要。此外，SOQ1 在体外和体内都容易在连接相邻管腔结构域的环处发生裂解，这可能是其抑制 qH 功能的调节过程。