Flaviviruses enter their host cells by receptor-mediated endocytosis, a well-orchestrated process of receptor recognition, penetration and uncoating. Recent findings on these early steps in the life cycle of flaviviruses are the focus of this review.
Keywords
FLAVIVIRUS; CELL ENTRY; RECEPTOR; ENDOCYTOSIS; ENVELOPE PROTEIN; PH ENVIRONMENT; STRUCTUREThe Flaviviridae are a family of small, enveloped RNA viruses that is comprised of three genera: Flavivirus, Hepacivirus, and Pestivirus. More than 70 viruses have been classified in the genus Flavivirus [1]. The genus includes various noteworthy mosquito-and tick-borne human pathogens, such as Yellow Fever virus (YFV), dengue virus (DENV), Tick-borne Encephalitis Virus (TBEV), and West Nile virus (WNV), that are subclassified into several antigenic complexes and phylogenetic groups [2]. Flaviviruses are typically associated with mild systemic disease, but can also cause severe symptoms such as hemorrhagic fever, encephalitis or death. Many of these viruses are resurgent, are spreading to new environments and are responsible for substantial morbidity and mortality around the globe. Flaviviruses are primarily transmitted through arthropod vectors. Humans and other mammals are not known to commonly develop infectious-level viremias and thus are probably incidental hosts with the exceptions of YFV, DENV and TBEV that are sufficiently well-adapted to a mammalian host.
The flavivirus lifecycleThe basic stages of the flavivirus life cycle include attachment to the cell surface, internalization into the host cell, transfer of the viral RNA genome into the cytoplasm, translation of the viral proteins, replication of the genomic RNA, assembly and maturation of the virions, and ultimately the release of progeny viruses from the cell.Flaviviruses are lipid-enveloped viruses (Fig. 1A). After recognition and attachment to specific receptor molecules on the surface of the cell, the virus is internalized into the host * Correspondence should be addressed to M.G.R. (mr@purdue.edu, Tel. 765-494-4911, FAX 765-496-1189).Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. . The polyprotein is subsequently glycosylated by cellular glycosyltransferases and cleaved by a combination of viral and host proteases to release three structural (C, prM, and E) and seven non-structural proteins (NS1, NS2a, NS2b, NS3, NS4a, NS4b, and NS5). NS3 and NS5 are the bestcharacterized non-structural proteins that assemble with several other viral and host proteins to form the replication complex. NS3 combines helicase/NTPase, serine protease, and RNA triphosphatase...