Meza-Padilla Isaac, McConkey Brendan J, Nissimov Jozef I
Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada.
Virus Evol. 2024 Sep 26;10(1):veae082. doi: 10.1093/ve/veae082. eCollection 2024.
Horizontal gene transfer events between viruses and hosts are widespread across the virosphere. In cyanophage-host systems, such events often involve the transfer of genes involved in photosynthetic processes. The genome of the lytic cyanophage Ma-LMM01 infecting the toxic, bloom-forming, freshwater NIES-298 contains a homolog of the () gene, which was probably transferred from a cyanobacterial host. The function of the NblA protein is to disassemble phycobilisomes, cyanobacterial light-harvesting complexes that can comprise up to half of the cellular soluble protein content. NblA thus plays an essential dual role in cyanobacteria: it protects the cell from high-light intensities and increases the intracellular nitrogen pool under nutrient limitation. NblA has previously been shown to interact with phycocyanin, one of the main components of phycobilisomes. Using structural modeling and protein-protein docking, we show that the NblA dimer of Ma-LMM01 is predicted to have a significantly higher binding affinity for NIES-298 phycocyanin (αβ) hexamers, compared to the host homolog. Protein-protein docking suggests that the viral NblA structural model is able to bind deeper into the phycocyanin groove. The main structural difference between the virus and host NblA appears to be an additional α-helix near the N-terminus of the viral NblA, which interacts with the inside of the phycocyanin groove and could thus be considered partly responsible for this deeper binding. Interestingly, phylogenetic analyses indicate that this longer was probably acquired from a different host. Based on infection experiments and previous findings, we propose that a higher binding affinity of the viral NblA to the host phycocyanin may represent a selective advantage for the virus, whose infection cycle requires an increased phycobilisome degradation rate that is not fulfilled by the NblA of the host.
病毒与宿主之间的水平基因转移事件在整个病毒圈中广泛存在。在噬蓝藻病毒-宿主系统中，此类事件通常涉及光合过程相关基因的转移。感染有毒、能形成水华的淡水蓝藻NIES-298的裂解性噬蓝藻病毒Ma-LMM01的基因组包含一个（）基因的同源物，该基因可能是从蓝藻宿主转移而来。NblA蛋白的功能是拆解藻胆体，藻胆体是蓝藻的光捕获复合体，其含量可占细胞可溶性蛋白的一半。因此，NblA在蓝藻中起着至关重要的双重作用：它保护细胞免受高光强度影响，并在营养限制条件下增加细胞内氮库。此前已证明NblA与藻胆体的主要成分之一藻蓝蛋白相互作用。通过结构建模和蛋白质-蛋白质对接，我们发现，与宿主同源物相比，Ma-LMM01的NblA二聚体预计对NIES-298藻蓝蛋白（αβ）六聚体具有显著更高的结合亲和力。蛋白质-蛋白质对接表明，病毒NblA的结构模型能够更深入地结合到藻蓝蛋白凹槽中。病毒和宿主NblA的主要结构差异似乎在于病毒NblA N端附近有一个额外的α螺旋，它与藻蓝蛋白凹槽内部相互作用，因此可能部分导致了这种更深的结合。有趣的是，系统发育分析表明，这个更长的片段可能是从不同的宿主获得的。基于感染实验和先前的研究结果，我们提出，病毒NblA对宿主藻蓝蛋白的更高结合亲和力可能代表了病毒的一种选择优势，因为病毒的感染周期需要提高藻胆体降解速率，而宿主的NblA无法满足这一要求。
