Correlation between structure, protein composition, morphogenesis and cytopathology of Glossina pallidipes salivary gland hypertrophy virus

Henry M. Kariithi, Jan W. M. van Lent, Sjef Boeren, Adly M. M. Abd-Alla, İkbal Agah İnce, Monique M. van Oers, Just M. Vlak

¹Laboratory of Virology, Wageningen University, 6708 PB Wageningen, The Netherlands

²Insect Pest Control Laboratory, International Atomic Energy Agency, A-1400 Vienna, Austria

³Laboratory of Biochemistry, Wageningen University, 6703 HA Wageningen, The Netherlands

⁴Department of Genetics and Bioengineering, Yeditepe University, 34755, Istanbul, Turkey

⁵Department of Biosystems Engineering, Faculty of Engineering, Giresun University, 28100, Giresun, Turkey

Correspondence
Monique M. van Oers monique.vanoers{at}wur.nl

Abstract

The Glossina pallidipes salivary gland hypertrophy virus (GpSGHV) is a dsDNA virus with rod-shaped, enveloped virions. Its 190 kb genome contains 160 putative protein-coding ORFs. Here, the structural components, protein composition and associated aspects of GpSGHV morphogenesis and cytopathology were investigated. Four morphologically distinct structures: the nucleocapsid, tegument, envelope and helical surface projections, were observed in purified GpSGHV virions by electron microscopy. Nucleocapsids were present in virogenic stroma within the nuclei of infected salivary gland cells, whereas enveloped virions were located in the cytoplasm. The cytoplasm of infected cells appeared disordered and the plasma membranes disintegrated. Treatment of virions with 1 % NP-40 efficiently partitioned the virions into envelope and nucleocapsid fractions. The fractions were separated by SDS-PAGE followed by in-gel trypsin digestion and analysis of the tryptic peptides by liquid chromatography coupled to electrospray and tandem mass spectrometry. Using the MaxQuant program with Andromeda as a database search engine, a total of 45 viral proteins were identified. Of these, ten and 15 were associated with the envelope and the nucleocapsid fractions, respectively, whilst 20 were detected in both fractions, most likely representing tegument proteins. In addition, 51 host-derived proteins were identified in the proteome of the virus particle, 13 of which were verified to be incorporated into the mature virion using a proteinase K protection assay. This study provides important information about GpSGHV biology and suggests options for the development of future anti-GpSGHV strategies by interfering with virus–host interactions.