viruses Article Parvovirus B19 Uncoating Occurs in the Cytoplasm without Capsid Disassembly and It Is Facilitated by Depletion of Capsid-Associated Divalent Cations 1 1 1, 1 2 Oliver Caliaro , Andrea Marti , Nico Ruprecht y, Remo Leisi , Suriyasri Subramanian , Susan Hafenstein 2,3 and Carlos Ros 1,* 1 Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland;
[email protected] (O.C.);
[email protected] (A.M.);
[email protected] (N.R.);
[email protected] (R.L.) 2 Department of Medicine, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA;
[email protected] (S.S.);
[email protected] (S.H.) 3 Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802, USA * Correspondence:
[email protected]; Tel.: +41-31-6314331 Present address: Department of Diagnostic, Interventional and Pediatric Radiology, University Hospital, y University of Bern, 3010 Bern, Switzerland. Received: 17 April 2019; Accepted: 9 May 2019; Published: 10 May 2019 Abstract: Human parvovirus B19 (B19V) traffics to the cell nucleus where it delivers the genome for replication. The intracellular compartment where uncoating takes place, the required capsid structural rearrangements and the cellular factors involved remain unknown. We explored conditions that trigger uncoating in vitro and found that prolonged exposure of capsids to chelating agents or to buffers with chelating properties induced a structural rearrangement at 4 ◦C resulting in capsids with lower density. These lighter particles remained intact but were unstable and short exposure to 37 ◦C or to a freeze-thaw cycle was sufficient to trigger DNA externalization without capsid disassembly.