Boogaard Bob, van Lent Jan W M, Theilmann David A, Erlandson Martin A, van Oers Monique M
Laboratory of Virology, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB Wageningen, the Netherlands.
Summerland Research and Development Centre, Agriculture and Agri-Food Canada, 4200 Highway #97, Summerland, BC, Canada.
J Gen Virol. 2017 Dec;98(12):3101-3110. doi: 10.1099/jgv.0.000974.
Baculoviruses orally infect caterpillars in the form of occlusion-derived viruses (ODVs). The ODV-envelope contains a number of proteins which are essential for oral infectivity, called infectivity factors (PIFs). Most of these PIFs are involved in the formation of an ODV-entry complex that consists of a stable core, formed by PIF1, PIF2, PIF3 and PIF4, and the more loosely associated PIFs P74 (PIF0) and P95 (PIF8). PIF1, PIF2 and PIF3 are essential for formation of the stable core, whereas deletion of the gene results in the formation of a smaller complex. P74 is not needed for formation of the stable core. We show here in larva-derived ODVs of the multicapsid nucleopolyhedrovirus that PIF-proteins are degraded by host-derived proteases after deletion of a single -gene. Constituents of the stable core-complex appeared to be more resistant to proteases as part of the complex than as monomer, as in ODVs of a deletion mutant only the stable core was found but no PIF monomers. When the stable core lacks PIF4, it lost its proteolytic resistance as the resulting smaller core complex was degraded in a deletion mutant. We also identified PIF6 as a loosely associated component of the entry complex that appeared nevertheless important for the proteolytic resistance of the stable core, which was degraded after deletion of . We conclude from these results that an intact entry-complex in the ODV-envelope is prerequisite for proteolytic resistance of PIF-proteins under the alkaline conditions of the larval midgut.
杆状病毒以包涵体衍生病毒（ODV）的形式经口感染毛虫。ODV包膜包含许多对经口感染至关重要的蛋白质，称为感染因子（PIF）。这些PIF中的大多数参与形成ODV进入复合体，该复合体由PIF1、PIF2、PIF3和PIF4形成的稳定核心以及关联较松散的PIF P74（PIF0）和P95（PIF8）组成。PIF1、PIF2和PIF3对稳定核心的形成至关重要，而该基因的缺失会导致形成较小的复合体。稳定核心的形成不需要P74。我们在此展示，在多粒包埋核多角体病毒的幼虫衍生ODV中，缺失单个基因后，PIF蛋白会被宿主衍生的蛋白酶降解。稳定核心复合体的成分作为复合体的一部分似乎比作为单体更能抵抗蛋白酶，如在一个缺失突变体的ODV中，只发现了稳定核心，而没有PIF单体。当稳定核心缺乏PIF4时，它失去了蛋白水解抗性，因为在一个缺失突变体中，由此产生的较小核心复合体被降解。我们还确定PIF6是进入复合体的一个松散关联成分，然而它似乎对稳定核心的蛋白水解抗性很重要，在缺失后该核心会被降解。我们从这些结果得出结论，在幼虫中肠的碱性条件下，ODV包膜中完整的进入复合体是PIF蛋白具有蛋白水解抗性的先决条件。
