malfunction |
the gain of function mutation 3/V132A as well as the mutations in the NS4A-kink region expose the TEV cleavage site suggesting a destabilization of the NS3/4A-kink interaction. Single mutations at the NS3/4A-kink interface allow for polyprotein processing and RNA replication. The gain of function mutation 3/V132A can be functionally substituted by the single mutations 4A/L45A or 4A/Y47A in NS2-3-independent virion morphogenesis. The replication-deficient NS3/4A double mutant 4A/L45-Y47-AA is functional in viral packaging when supplied in trans. Analysis of NS3 and NS2 mutations combined, overview |
Classical swine fever virus |
metabolism |
upon infection of the host cell the viral RNA genome is translated into a polyprotein that is processed by cellular and viral proteases into the mature structural (SP) and nonstructural (NS) proteins. For members of the genus Pestivirus the array in the polyprotein is the following: NH2-Npro (N-terminal autoprotease), C (capsid protein, core), Erns (envelope protein RNase secreted), E1, E2, p7, NS2-3 (NS2 and NS3), NS4A, NS4B, NS5A, NS5B-COOH. The N-terminal autoprotease Npro generates its own C-terminus and thereby the N-terminus of the capsid protein core (C). Further cleavages releasing the structural proteins C, Erns, E1 and E2 as well as p7 are mediated by proteases residing in the endoplasmatic reticulum (ER). The cleavage between NS2 and NS3 is catalyzed by an autoprotease in NS2. The activity of the NS2 protease is temporally regulated by a cellular cofactor leading to significant amounts of uncleaved NS2-3 in pestivirus infected cells. The cleavages downstream of NS3, NS4A, NS4B and NS5A are catalyzed by the serine protease domain of NS3 which requires NS4A as cofactor for full proteolytic activity and is termed NS3-4A protease |
Classical swine fever virus |
additional information |
structure-function analysis suggests that NS3/4A can adopt two different conformations in the infected cell, a closed form that is used in RNA replication complexes and a more open conformation functional in viral assembly. Furthermore, the NS2-3/4A complex, required for virion assembly of prototype pestiviruses, displays a similar open conformation. CSFV NS3/4A complex crystal structure analysis, overview |
Classical swine fever virus |
physiological function |
cleavages downstream of NS3, NS4A, NS4B and NS5A, former parts of the viral polyprotein, are catalyzed by the serine protease domain of NS3 which requires NS4A as cofactor for full proteolytic activity and is termed NS3-4A protease. A special feature of pestiviruses is the existence of significant amounts of uncleaved NS2-3 in the infected cell and its essential role in virion formation, temporal restriction of NS2-3 processing by the NS2 autoprotease, mostly restricted to the early phase of infection. NS2-3 translated at later time points is only inefficiently processed leading to the accumulation of uncleaved NS2-3 which temporally correlates with the onset of virion morphogenesis. Downregulation of NS2-3 processing plays a crucial role for the non-cytopathogenic (ncp) biotype of pestiviruses in cell culture |
Classical swine fever virus |