The C-terminal 18 Amino Acid Region of Dengue Virus NS5 Regulates its Subcellular Localization and Contains a Conserved Arginine Residue Essential for Infectious Virus Production.
Dengue virus NS5 is the most highly conserved amongst the viral non-structural proteins and is responsible for capping, methylation and replication of the flavivirus RNA genome. Interactions of NS5 with host proteins also modulate host immune responses. Although replication occurs in the cytoplasm, an unusual characteristic of DENV2 NS5 is that it localizes to the nucleus during infection with no clear role in replication or pathogenesis. We examined NS5 of DENV1 and 2, which exhibit the most prominent difference in nuclear localization, employing a combination of functional and structural analyses. Extensive gene swapping between DENV1 and 2 NS5 identified that the C-terminal 18 residues (Cter18) alone was sufficient to direct the protein to the cytoplasm or nucleus, respectively. The low micromolar binding affinity between NS5 Cter18 and the nuclear import receptor importin-alpha (Impα), allowed their molecular complex to be purified, crystallised and visualized at 2.2 Å resolution using x-ray crystallography. Structure-guided mutational analysis of this region in GFP-NS5 clones of DENV1 or 2 and in a DENV2 infectious clone reveal residues important for NS5 subcellular localization. Notably, the trans conformation adopted by Pro-884 allows proper presentation for binding Impα and mutating this proline to Thr, as present in DENV1 NS5, results in mislocalizaion of NS5 to the cytoplasm without compromising virus fitness. In contrast, a single mutation to alanine at NS5 position R888, a residue conserved in all flaviviruses, resulted in a completely non-viable virus, and the R888K mutation led to a severely attenuated phentoype, even though NS5 was located in the nucleus. R888 forms a hydrogen bond with Y838 that is also conserved in all flaviviruses. Our data suggests an evolutionarily conserved function for NS5 Cter18, possibly in RNA interactions that are critical for replication, that is independent of its role in subcellular localization.
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.
Moon Y F
MY
Tay
School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, New South Wales, Australia.
Kate
K
Smith
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.
Ivan H W
IH
Ng
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.|Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Kitti W K
KW
Chan
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.
Yongqian
Y
Zhao
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.|Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Eng Eong
EE
Ooi
School of Biological Sciences, Nanyang Technological University, Singapore.|UPMC UMRS CR7-CNRS ERL 8255-INSERM U1135 Centre d'Immunologie et des Maladies Infectieuses. Centre Hospitalier Universitaire Pitié-Salpêtrière, Faculté de Médecine Pierre et Marie Curie, Paris, France.
Julien
J
Lescar
Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.
Dahai
0000-0001-7637-7275
D
Luo
Nuclear Signalling Laboratory, Department of Biochemistry and Molecular Biology, Monash University, Melbourne, Victoria, Australia.
David A
DA
Jans
School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, New South Wales, Australia.
Jade K
JK
Forwood
Program in Emerging Infectious Diseases, Duke-NUS Medical School, Singapore.|Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Subhash G
0000-0002-5083-3831
SG
Vasudevan
D021581:Active Transport, Cell Nucleus; D019943:Amino Acid Substitution; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism* / Q000821:virology; D006224:Cricetinae; D003716:Dengue Virus / Q000502:physiology*; D006801:Humans; D020125:Mutation, Missense; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism*; D000072417:Protein Domains; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
C582223:NS5 protein, dengue virus; D019913:Nuclear Localization Signals; D017361:Viral Nonstructural Proteins