State Key Laboratory of Rice Biology and Ministry of Agriculture Key Laboratory of Molecular Biology of Crop Pathogens and Insects, Institute of Biotechnology, Zhejiang University, Hangzhou 310058, China.
State Key Laboratory for Managing Biotic and Chemical Threats to the Quality and Safety of Agro-Products, Institute of Virology and Biotechnology, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China.
Viruses. 2021 Sep 28;13(10):1949. doi: 10.3390/v13101949.
Most endolysins of dsDNA phages are exported by a holin-dependent mechanism, while in some cases endolysins are exported via a holin-independent mechanism. However, it is still unclear whether the same endolysins can be exported by both holin-dependent and holin-independent mechanisms. This study investigated the lysis system of OP2-like phage X2 infecting pv. , causing devastating bacterial leaf blight disease in rice. Based on bioinformatics and protein biochemistry methods, we show that phage X2 employs the classic "holin-endolysin" lysis system. The endolysin acts on the cell envelope and exhibits antibacterial effects in vitro, while the holin facilitates the release of the protein into the periplasm. We also characterized the role of the transmembrane domain (TMD) in the translocation of the endolysin across the inner membrane. We found that the TMD facilitated the translocation of the endolysin via the Sec secretion system. The holin increases the efficiency of protein release, leading to faster and more efficient lysis. Interestingly, in , the expression of either holin or endolysin with TMDs resulted in the formation of long rod shaped cells. We conclude that the TMD of X2-Lys plays a dual role: One is the transmembrane transport while the other is the inhibition of cell division, resulting in larger cells and thus in a higher number of released viruses per cell.
大多数双链 DNA 噬菌体的内溶素都是通过依赖于孔蛋白的机制进行输出的，而在某些情况下，内溶素是通过非依赖于孔蛋白的机制进行输出的。然而，目前仍不清楚是否可以通过依赖于孔蛋白和非依赖于孔蛋白的两种机制来共同输出相同的内溶素。本研究调查了感染 pv. 的 OP2 样噬菌体 X2 的裂解系统，这种噬菌体导致了水稻细菌性叶斑病的毁灭性爆发。通过生物信息学和蛋白质生化方法，我们表明噬菌体 X2 采用了经典的“孔蛋白-内溶素”裂解系统。内溶素作用于细胞包膜，并在体外表现出抗菌作用，而孔蛋白则促进蛋白释放到周质中。我们还研究了跨膜结构域（TMD）在内溶素跨内膜转运中的作用。我们发现 TMD 促进了内溶素通过 Sec 分泌系统的转运。孔蛋白提高了蛋白释放的效率，从而导致更快、更有效的裂解。有趣的是，在 pv. 中，带有 TMD 的孔蛋白或内溶素的表达都会导致长杆状细胞的形成。我们得出结论，X2-Lys 的 TMD 发挥了双重作用：一方面是跨膜转运，另一方面是抑制细胞分裂，导致细胞更大，从而使每个细胞释放的病毒数量更多。
