Characterization of the structure and function of the glycoprotein of the novel rhabdovirus Mangala virus and identification of its cellular receptor
Final Report Abstract
The goal of the present project was to characterize the structural and functional requirements of the glycoprotein of the novel rhabdovirus Bas-Congo virus (BASV, formerly known as Mangala virus) and to identify its cellular receptor. BASV was discovered by next-generation sequencing in a hemorrhagic fever patient in the Democratic Republic of Congo. While a link between BASV infection and the observed symptomatic disease still needs to be established, it was shown as part of this project that serological evidence for BASV exposure is detectable in a fraction of the human population in Central Africa. For this purpose, serological assays for the specific detection of antibodies against the BASV glycoprotein (G), nucleoprotein (N), and matrix protein (M) were developed, and 2,430 serum samples from five Central African countries were screened for BASV- specific antibodies. These novel serological assays may become useful tools in future surveillance and diagnostic efforts. The structural analysis of BASV-G revealed several similarities with other rhabdovirus glycoproteins, such as an essential bipartite fusion loop motif and the requirement of low pH for fusion activation. The conformational changes induced in BASV-G by low pH were fully reversible, and the main route of BASV-G mediated cell entry was endocytosis. It was further determined that BASV-G contains complex, high-mannose N-linked glycans that contribute about 14% of its molecular weight. In contrast to closely related arthropod-borne rhabdovirus glycoproteins, BASV-G required temperatures ≥ 37°C for optimal fusogenic activity, suggesting a strong adaptation to mammalian or avian hosts. Another distinctive feature of BASV-G is its use of cellular lectins as attachment factors, which may have important implications for BASV transmission between hosts and dissemination within infected individuals. While the identity of the cellular BASV receptor could not be revealed by the end of this funding period, several hints at its molecular characteristics could be established. It was found that N-linked glycans on the cell surface play an important role in BASV-G mediated cell entry, while a proteinaceous component was required as well. Evidence further suggests that the putative BASV receptor relies on divalent cations for its structural stability. BASV-G binding to Vero cells may further involve attachment factors that are not essential for BASV-G mediated cell entry. Taken together the results obtained in the present project substantially increase our understanding of the epidemiology and molecular biology of the novel rhabdovirus BASV and create new starting points for follow-up studies, such as the identification of the natural BASV reservoir and a possible application of BASV-G in gene therapy.
Publications
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(2013) Characterization of the Bas-Congo virus glycoprotein and its function in pseudotyped viruses. J Virol., 87(17):9558-68
Steffen I, Liss NM, Schneider BS, Fair JN, Chiu CY, Simmons G
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(2015) Emerging Rhabdoviruses. In Biology and Pathogenesis of Rhabdo- and Filoviruses, Editors: A. K. Pattnaik and M. A. Whitt, World Scientific, p. 311-334
Steffen I and Simmons G
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(2016) Pseudotyping viral vectors with emerging virus envelope proteins. Current Gene Therapy, 16(1):47-55
Steffen I and Simmons G
