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Journal of Virology, February 2009, p. 1511-1522, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01381-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Low-pH Triggering of Human Metapneumovirus Fusion: Essential Residues and Importance in Entry{triangledown}

Rachel M. Schowalter,1 Andres Chang,1 Jessica G. Robach,2 Ursula J. Buchholz,3 and Rebecca Ellis Dutch1*

Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, Kentucky 40536-0509,1 Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern University, Evanston, Illinois 60208,2 Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892-80073

Received 2 July 2008/ Accepted 13 November 2008

Human metapneumovirus (HMPV) is a significant respiratory pathogen classified in the Pneumovirinae subfamily of the paramyxovirus family. Recently, we demonstrated that HMPV F protein-promoted cell-cell fusion is stimulated by exposure to low pH, in contrast to what is observed for other paramyxovirus F proteins. In the present study, we examined the potential role of histidine protonation in HMPV F fusion and investigated the role of low pH in HMPV viral entry. Mutagenesis of the three ectodomain histidine residues of the HMPV F protein demonstrated that the mutation of a histidine in the heptad repeat B linker domain (H435) ablated fusion activity without altering cell surface expression or proteolytic processing significantly. Modeling of the HMPV F protein revealed several basic residues surrounding this histidine residue, and the mutation of these residues also reduced fusion activity. These results suggest that electrostatic repulsion in the heptad repeat B linker region may contribute to the triggering of HMPV F. In addition, we examined the effect of inhibitors of endosomal acidification or endocytosis on the entry of a recombinant green fluorescent protein-expressing HMPV. Interestingly, chemicals that raise the pH of endocytic vesicles resulted in a 30 to 50% decrease in HMPV infection, while the inhibitors of endocytosis reduced infection by as much as 90%. These data suggest that HMPV utilizes an endocytic entry mechanism, in contrast to what has been hypothesized for most paramyxoviruses. In addition, our results indicate that HMPV uses the low pH of the endocytic pathway to enhance infectivity, though the role of low pH likely differs from classically described mechanisms.

* Corresponding author. Mailing address: Department of Molecular and Cellular Biochemistry, University of Kentucky College of Medicine, Biomedical Biological Sciences Research Building, 741 South Limestone, Lexington, KY 40536-0509. Phone: (859) 323-1795. Fax: (859) 323-1037. E-mail: rdutc2{at}uky.edu

{triangledown} Published ahead of print on 26 November 2008.

Journal of Virology, February 2009, p. 1511-1522, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01381-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Qin, Z.-l., Zheng, Y., Kielian, M. (2009). Role of Conserved Histidine Residues in the Low-pH Dependence of the Semliki Forest Virus Fusion Protein. J. Virol. 83: 4670-4677 [Abstract] [Full Text]  


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