A PDI Family Network Acts Distinctly and Coordinately with ERp29 To Facilitate Polyomavirus Infection

Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Journal of Virology (Impact Factor: 4.44). 03/2011; 85(5):2386-96. DOI: 10.1128/JVI.01855-10
Source: PubMed


Endoplasmic reticulum (ER)-to-cytosol membrane transport is a decisive infection step for the murine polyomavirus (Py). We
previously determined that ERp29, a protein disulfide isomerase (PDI) member, extrudes the Py VP1 C-terminal arm to initiate
ER membrane penetration. This reaction requires disruption of Py's disulfide bonds. Here, we found that the PDI family members
ERp57, PDI, and ERp72 facilitate virus infection. However, while all three proteins disrupt Py's disulfide bonds in vitro, only ERp57 and PDI operate in concert with ERp29 to unfold the VP1 C-terminal arm. An alkylated Py cannot stimulate infection,
implying a pivotal role of viral free cysteines during infection. Consistent with this, we found that although PDI and ERp72
reduce Py, ERp57 principally isomerizes the virus in vitro, a reaction that requires viral free cysteines. Our mutagenesis study subsequently identified VP1 C11 and C15 as important
for infection, suggesting a role for these residues during isomerization. C11 and C15 also act together to stabilize interpentamer
interactions for a subset of the virus pentamers, likely because some of these residues form interpentamer disulfide bonds.
This study reveals how a PDI family functions coordinately and distinctly to promote Py infection and pinpoints a role of
viral cysteines in this process.

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Available from: Christopher P. Walczak, Feb 20, 2014
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    • "Thus, despite being in the same protein family, distinct PDI members execute unique roles in priming SV40 for ER membrane transport. In the case of the murine PyV, a noncatalytic PDI family member called ERp29 acts in concert with ERp57 and PDI to remodel the VP1 C-terminal arm (Walczak & Tsai, 2011), destabilizing the viral structure to generate a hydrophobic virus (Magnuson et al., 2005); the human JC PyV was also reported to hijack the activities of the ERp57-PDI-ERp29 triad during infection (Nelson et al., 2012). Another virus reported to reach the ER during infection is the human papillomavirus (HPV) (Disbrow et al., 2005; Zhang et al., 2014), raising the possibility that HPV might also penetrate the ER membrane to access the cytosol during entry. "
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    • "Virions are internalized into smooth endocytic vesicles [3], [6], [8], often positive for caveolin-1 [5], [6], and subsequently fuse with larger endosomes [3], [5], [6], [9]. Like other polyomaviruses, MPyV virions do not escape the endosomal system until they reach the lumen of smooth endoplasmic reticulum (ER) [5], [6], [9], [10], where lumenal enzymes facilitate virus capsid disassembly and uncoating of viral genomes prior to their import into the nucleus [11]–[13]. Regardless of the multiplicity of infection, only a few virions are able to deliver their genomic DNA into the cell nucleus [10]. Currently, two possible ways for viral genome delivery to the cell nucleus have been proposed: either partially disassembled virions translocate from ER to the cytosol and then are imported into the nucleus via nuclear pore complexes or, alternatively, they penetrate directly from ER to the nucleoplasm through the nuclear envelope (reviewed in [14]). "
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    • "In SV40 , cysteine 9 ( C9 ) and C104 form inter - pentameric disulfide bonds with adjacent pentamers to link the capsid together , and a disulfide bond at C15 has been shown to be important in mPy ( Schelhaas et al . , 2007 ; Walczak and Tsai , 2011 ) . Cysteine residues 104 and 257 are conserved in JCV ; however , JCV lacks the C9 , and likely engages these ER enzymes in a similar , but not identical fashion . "
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