Home » Key Scientific Articles » The putative herpes simplex virus 1 chaperone protein UL32 modulates disulfide bond formation during infection

The putative herpes simplex virus 1 chaperone protein UL32 modulates disulfide bond formation during infection

Albright BS1, Kosinski A1, Szczepaniak R1, Cook EA2, Stow ND2, Conway JF3, Weller SK4.

J Virol. 2015 Jan;89(1):443-53.

1Department of Molecular Biology and Biophysics and the Molecular Biology and Biochemistry Graduate Program, University of Connecticut Health Center, Farmington, Connecticut, USA.and

2MRC-University of Glasgow Centre for Virus Research (CVR), Glasgow, United Kingdom.and

3Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.and

4Department of Molecular Biology and Biophysics and the Molecular Biology and Biochemistry Graduate Program, University of Connecticut Health Center, Farmington, Connecticut, USA.

Contact: [email protected]

 

Abstract

During DNA encapsidation, herpes simplex virus 1 (HSV-1) procapsids are converted to DNA-containing capsids by a process involving activation of the viral protease, expulsion of the scaffold proteins, and the uptake of viral DNA. Encapsidation requires six minor capsid proteins (UL6, UL15, UL17, UL25, UL28, and UL33) and one viral protein, UL32, not found to be associated with capsids. Although functions have been assigned to each of the minor capsid proteins, the role of UL32 in encapsidation has remained a mystery. Using an HSV-1 variant containing a functional hemagglutinin-tagged UL32, we demonstrated that UL32 was synthesized with true late kinetics and that it exhibited a previously unrecognized localization pattern. At 6 to 9 h postinfection (hpi), UL32 accumulated in viral replication compartments in the nucleus of the host cell, while at 24 hpi, it was additionally found in the cytoplasm. A newly generated UL32-null mutant was used to confirm that although B capsids containing wild-type levels of capsid proteins were synthesized, these procapsids were unable to initiate the encapsidation process. Furthermore, we showed that UL32 is redox sensitive and identified two highly conserved oxidoreductase-like C-X-X-C motifs that are essential for protein function. In addition, the disulfide bond profiles of the viral proteins UL6, UL25, and VP19C and the viral protease, VP24, were altered in the absence of UL32, suggesting that UL32 may act to modulate  disulfide bond formation during procapsid assembly and maturation.

IMPORTANCE:

Although functions have been assigned to six of the seven required packaging proteins of HSV, the role of UL32 in encapsidation has remained a mystery. UL32 is a cysteine-rich viral protein that contains C-X-X-C motifs reminiscent of those in proteins that participate in the regulation of disulfide bond formation. We have previously demonstrated that  disulfide bonds are required for the formation and stability of the viral capsids and  are also important for the formation and stability of the UL6 portal ring. In this report, we demonstrate that the disulfide bond profiles of the viral proteins UL6, UL25, and VP19C and the viral protease, VP24, are altered in cells infected with a newly isolated UL32-null mutant virus, suggesting that UL32 acts as a chaperone capable of modulating disulfide bond formation. Furthermore, these results suggest that proper regulation of disulfide bonds is essential for initiating encapsidation.

Copyright © 2015, American Society for Microbiology. All Rights Reserved.

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