The DI–DII linker of human parainfluenza virus type 3 fusion protein is critical for the virus
Human parainfluenza virus type 3 (HPIV3) causes the majority of childhood viral pneumonia around the world. Fusing the viral and target cell membranes is crucial for its entry into target cells, and the fusion process requires the concerted actions of two viral glycoproteins: hemagglutinin-neuraminidase (HN) and fusion (F) protein. After binding to the cell surface receptor, sialic acids, HN triggers F to undergo large conformational rearrangements to execute the fusion process. Although it has been reported that several domains of F had important impacts on regulating the membrane fusion activity, what role the DI–DII linker (residues 369–374, namely L1 linker) of the HPIV3 F protein plays in the fusion process still remains confused. We have obtained three chimeric mutant proteins (Ch-NDV-L1, Ch-MV-L1, Ch-HPIV1-L1) containing the full length of HPIV3 F protein but their corresponding DI–DII linker derived from the F protein of Newcastle disease virus (NDV), Measles virus (MV), and Human parainfluenza virus type 1 (HPIV1), respectively. One deletion mutant protein (De-L1), whose DI–DII linker was deleted, has been established simultaneously. Then vaccinia virus-T7 RNA polymerase transient expression system and standard plasmid system were utilized to express the mutant F proteins in BHK-21 cells. These four mutants were determined for membrane fusogenic activity, cell surface expression level, and total mutant F protein expression. All of them resulted in a significant reduction in fusogenic activity in all steps of cell–cell membrane fusion process. There was no significant difference in cell surface protein expression level for the mutants compared with wild-type F. The mutant proteins with inability in fusogenic activity were all at the form of precursor protein, F0, which were not hydrolyzed by intracellular protease furin. The results above suggest that the involvement of the DI–DII linker region is necessary for the complete fusion of the membranes.
KeywordsHuman parainfluenza virus type 3 Fusion protein Membrane fusion Mutation analysis
We gratefully acknowledge Dr. Ronald Iorio for providing the recombinant plasmid vectors and Dr. Bernard Moss for the recombinant vaccinia virus, vTF7-3. BHK-21 cells were kindly provided by the Center for Disease Control and Prevention, Shandong, China.
Designed study: YL, MC, ZW. Performed research: YL, MC, NL. Analyzed data: YL, MC, ZW. Prepared/Evaluated experiment: YL, HLW, LZ, YYS. Wrote the paper: YL. Revised manuscript: ZW.
This study was funded by the National Natural Science Foundation of China (Nos. 81672011, 81271806) and the Fundamental search Funds of Shandong University (2015JC044).
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interest.
Present paper does not contain any studies with human participants or animals performed by any of the authors. Ethics Committee of School of Public Health, Shandong University approved this study.
Informed consent was obtained from all individual participants in the study.
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