Department of Biological Sciences, School of Medical and Life Sciences, Sunway University, Bandar Sunway 47500, Malaysia.
Department of Medical Sciences, School of Medical and Life Sciences, Sunway University, Bandar Sunway 47500, Malaysia.
Toxins (Basel). 2023 Jun 13;15(6):396. doi: 10.3390/toxins15060396.
actinoporin-like toxin 4 (HALT-4) differs from other actinoporins due to its N-terminal propart that contains approximately 103 additional residues. Within this region, we identified five dibasic residues and assumed that, when cleaved, they could potentially exhibit HALT-4's cytolytic activity. We created five truncated versions of HALT-4 (tKK1, tKK2, tRK3, tKK4 and tKK5) to investigate the role of the N-terminal region and potential cleavage sites on the cytolytic activity of HALT-4. However, our results demonstrated that the propart-containing HALT-4 (proHALT-4), as well as the truncated versions tKK1 and tKK2, exhibited similar cytolytic activity against HeLa cells. In contrast, tRK3, tKK4 and tKK5 failed to kill HeLa cells, indicating that cleavage at the KK1 or KK2 sites did not enhance cytolytic activity but may instead facilitate the sorting of tKK1 and tKK2 to the regulated secretory pathway for eventual deposition in nematocysts. Moreover, RK3, KK4 and KK5 were unlikely to serve as proteolytic cleavage sites, as the amino acids between KK2 and RK3 are also crucial for pore formation.
肌动蛋白样毒素 4（HALT-4）因其 N 端前导区含有约 103 个额外的残基而有别于其他肌动蛋白。在这个区域内，我们鉴定了五个双碱性残基，并假设它们在被切割时可能会表现出 HALT-4 的细胞毒性活性。我们构建了 HALT-4 的五个截断版本（tKK1、tKK2、tRK3、tKK4 和 tKK5），以研究 N 端区域和潜在切割位点对 HALT-4 细胞毒性活性的作用。然而，我们的结果表明，含有前导区的 HALT-4（proHALT-4）以及截断版本 tKK1 和 tKK2，对 HeLa 细胞表现出相似的细胞毒性活性。相比之下，tRK3、tKK4 和 tKK5 未能杀死 HeLa 细胞，表明在 KK1 或 KK2 位点的切割并没有增强细胞毒性活性，但可能会促进 tKK1 和 tKK2 向调节性分泌途径的分拣，以便最终沉积在刺丝囊中。此外，RK3、KK4 和 KK5 不太可能作为蛋白水解切割位点，因为 KK2 和 RK3 之间的氨基酸对于孔形成也很关键。
