Channel Catfish Virus Gene 50 Encodes a Secreted, Mucin-like Glycoprotein

Abstract

Cells infected with the wild-type (WT) strain of channel catfish virus (CCV) secreted a glycoprotein with an apparent molecular mass (MM) superior to 200 kDa into the culture medium. This protein, designated gp250, was the sole viral glycoprotein detected in the culture medium after [3H]mannose labeling of the infected cells. When cells were infected with the attenuated V60 strain, a glycoprotein of 135 kDa (designated gp135) was detected instead of gp250. Because WT gene 50 is predicted to encode a secreted, mucin-type glycoprotein, we expressed this gene transiently and detected a glycoprotein of the same apparent MM as gp250 in the culture medium of transfected catfish cells. The increased mobility in SDS-PAGE of the secreted V60 glycoprotein correlated with the presence of a major deletion in V60 gene 50. Therefore, we concluded that gp250 in the WT and gp135 in the V60 strains are both likely encoded by gene 50. An important shift in the relative mobility of gp250 in SDS-PAGE was observed after tunicamycin treatment of infected cells labeled with [3H]glucosamine, confirming the presence of N-linked sugars on gp250. We observed variations in the size of PCR products derived from gene 50 amplification in three different field isolates. Such genetic variations are a characteristic feature of mucin genes and are linked to crossing-over events between internal repeated sequences, such as those present in gene 50.

Systemic herpes-like virus in catfishIctalurus melas(Italy) differs from Ictalurid herpesvirus 1 (North America)

“…All the remaining herpesviruses known from fish are currently unassigned members of the family Herpesviridae. The entire genome of 1 CCV isolate has been sequenced, and in-depth studies have investigated both the structure and function of selected genes and gene products of the virus (Davison 1992, 1998, 2002, Hanson et al 1994, Davison & Davison 1995, Booy et al 1996, Kucuktas & Brady 1999, Vanderheijden et al 1999.…”

Relaxed Selection and the Evolution of RNA Virus Mucin-Like Pathogenicity Factors

“…This virus is a herpesvirus encoding a mucin that exhibits a repeat structure reminiscent of those of eukaryotic mucins. The channel catfish virus mucin may also be a pathogenicity factor, as a strain lacking this gene is attenuated (20,21). The nonrepetitive viral MLRs described here may represent a novel way in which viruses can evolve pathogenicity factors.…”

Herpesviruses of Fish, Amphibians and Invertebrates

“…Based on the localization of the structural proteins in the different virion compartments, several of these proteins could be functionally characterized. Two alloherpesvirus proteins have been characterized in more detail: IcHV-1 ORF50 has been shown to encode a secreted mucin-like glycoprotein (Vanderheijden et al, 1999), and CyHV-3 ORF81 has been identified as an envelope protein (Rosenkranz et al, 2008).…”