Chaperone-Mediated In Vitro Disassembly of Polyoma- and Papillomaviruses

Abstract

Hsp70 chaperones play a role in polyoma-and papillomavirus assembly, as evidenced by their interaction in vivo with polyomavirus capsid proteins at late times after virus infection and by their ability to assemble viral capsomeres into capsids in vitro. We studied whether Hsp70 chaperones might also participate in the uncoating reaction. In vivo, Hsp70 coimmunoprecipitated with polyomavirus virion VP1 at 3 h after infection of mouse cells. In vitro, prokaryotic and eukaryotic Hsp70 chaperones efficiently disassembled polyoma-and papillomavirus-like particles and virions in energy-dependent reactions. These observations support a role for cell chaperones in the disassembly of these viruses.The Papillomaviridae and Polyomaviridae are small, nonenveloped DNA viruses that have structurally similar 50-to 55-nm-diameter capsids comprised of 72 capsomeres arranged in a T ϭ 7 icosahedral lattice (2). Each capsomere is a pentamer of the major capsid protein: L1 for papillomavirus and VP1 for polyomavirus. The carboxy terminus of L1 or VP1 mediates interpentameric contacts in the assembled capsid (13,16,17,22). These contacts are stabilized by disulfide bonds for papillomaviruses (15,21,29) or by both disulfide bonds and calcium bridges for polyomaviruses (4,5,14).

How Viruses Use the Endoplasmic Reticulum for Entry, Replication, and Assembly

“…Furthermore, although there is evidence implicating the proteasome at this stage (Schelhaas et al 2007;Jiang et al 2009b;, it is unlikely to play a direct role. If cytosol release and virus disassembly are coupled, the cytosolic chaperone Hsc70 may be the ideal candidate for catalyzing the release step as it disassembles Py in vitro (Chromy et al 2006). Because all of these proposed cytosolic factors play many other cellular functions, whether they execute a direct role in catalyzing Py release into the cytosol remains inconclusive.…”

Replication and Assembly of Human Papillomaviruses

“…These same experiments utilizing L2-deficient native virions depicted a role for L2 in DNA encapsidation and/or structural stability of the virions, since fewer DNase-resistant genomes were detected in the L2-deficient samples when compared with the wild-type native virions (Holmgren et al, 2005). Over the years, many publications have cited the appearance of viral and/or cellular factors that co-purify with native virions, such as E2, E4, E5, E7, and histones (Doorbar and Gallimore, 1987;Larsen et al, 1987;Heino et al, 2000;Fligge et al, 2001;Chromy et al, 2003Chromy et al, , 2006Gu et al, 2004;Bordeaux et al, 2006;Richards et al, 2006;Kondo et al, 2007;Bird et al, 2008;Buck et al, 2008).…”

“…Also housed within the virion is a histone-associated, 8-kb, circular viral genome which has been shown to alter the final structure of the virion (Sapp et al, 1998;Fligge et al, 2001). In addition to L2 and viral DNA, a minority population of unknown viral and/or cellular proteins/factors such as molecular chaperones and karyopherins may also exist which influence the final structure of native virions (Chromy et al, 2003(Chromy et al, , 2006Bird et al, 2008).…”

“…that may either directly or indirectly affect the structure of the capsid (Doorbar and Gallimore, 1987;Larsen et al, 1987;Heino et al, 2000;Fligge et al, 2001;Chromy et al, 2003Chromy et al, , 2006Gu et al, 2004;Bordeaux et al, 2006;Richards et al, 2006;Kondo et al, 2007;Bird et al, 2008;Buck et al, 2008). Many other unknown viral and/or cellular factors are undoubtedly necessary for the proper assembly of native virions regarding regulation of redox states within the cell, proper cellular localization and initial interaction of capsid proteins, the correct formation/regulation of disulfide bonds, and regulation of capsid protein expression.…”

“…Similarly, the L1 and L2 capsid proteins are expressed only in terminally differentiated keratinocytes (Barksdale and Baker, 1993). Studies with both papillomaviruses and polyomaviruses suggest that, once expressed, capsid proteins assemble into icosahedral capsids via assistance from chaperone proteins (Buck et al, 2005;Chromy et al, 2003Chromy et al, , 2006Bird et al, 2008). It is unknown if encapsidation of the viral genome takes place during capsid assembly or after; however, encapsidation is assisted by L2 and may be facilitated by E2 proteins (Heino et al, 2000;Gu et al, 2004;Holmgren et al, 2005).…”