title: A PDI family network acts distinctly and coordinately with ERp29 to facilitate polyomavirus infection.
abstract: 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.
authors.affiliation: Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Walczak
authors.forename: Billy
authors.initials: B
authors.lastname: Tsai
mesh_terms: D000818:Animals; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000235:genetics / Q000378:metabolism / Q000821:virology; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D011120:Polyomavirus / Q000502:physiology*; D027601:Polyomavirus Infections / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism*
chemical_list: C491738:ERP29 protein, human; D006360:Heat-Shock Proteins; D008562:Membrane Glycoproteins; C062477:endoplasmic reticulum glycoprotein p72; D019704:Protein Disulfide-Isomerases; C085868:PDIA3 protein, human