Capsid assembly is regulated by amino acid residues asparagine 47 and 48 in the VP2 protein of porcine parvovirus

Jucai Wang,Yunchao Liu,Yumei Chen,Teng Zhang,Aiping Wang,Qiang Wei,Dongmin Liu,Fangyu Wang,Gaiping Zhang

doi:10.1016/j.vetmic.2020.108974

Abstract

Porcine parvovirus (PPV) is a major cause of reproductive failure in swine and has caused substantial losses throughout the world. Viral protein 2 (VP2) of PPV is a major structural protein that can self-assemble into virus-like particles (VLP) with hemagglutination (HA) activity. In order to identify the essential residues involved in the mechanism of capsid assembly and to further understand the function of HA, we analyzed a series of deletion mutants and site-directed mutations within the N-terminal of VP2 using the Escherichia coli system. Our results showed that deletion of the first 47 amino acids from the N-terminal of the VP2 protein did not affect capsid assembly, and further truncation to residue 48 Asparagine (Asn, N) caused detrimental effects. Site-directed mutagenesis experiments demonstrated that residue 47Asn reduced the assembly efficiency of PPV VLP, while residue 48Asn destroyed the stability, hemagglutination, and self-assembly characteristics of the PPV VP2 protein. Results from native PAGE inferred that macromolecular polymers were critical intermediates of the VP2 protein during the capsid assembly process. Site-directed mutation at 48Asn did not affect the ability of monomers to form into oligomers, but destroyed the ability of oligomers to assemble into macromolecular particles, influencing both capsid assembly and HA activity. Our findings provide valuable information on the mechanisms of PPV capsid assembly and the possibility of chimeric VLP vaccine development by replacing the first 47 amino acids at the N-terminal of the VP2 protein.

Highlights

Porcine parvovirus (PPV) is a major cause of reproductive failure in swine, and has caused huge losses throughout the world
Our results demonstrated that PPV capsid assembly is a complex process that is regulated by amino acids 47Asn and 48Asn, which are located at the N-terminal of Viral protein 2 (VP2) and closely related to the association of macromolecular particles
The mechanisms of PPV capsid assembly remains unclear, our data suggested that sitedirected mutagenesis at 48Asn did not affect the association of monomers to form into oligomers, but destroyed the ability of oligomers to assemble into macromolecular particles

Summary

Introduction

Porcine parvovirus (PPV) is a major cause of reproductive failure in swine, and has caused huge losses throughout the world. Viral protein 2 (VP2) of PPV is a major structural protein that can selfassemble into virus-like particles (VLP) with hemagglutination (HA) activity. Porcine parvovirus (PPV), a member of the genus Parvovirus, family Parvoviridae, is a common pathogen associated with reproductive failure in swine [1, 2]. It is a single-stranded DNA virus, which packages its DNA into a T = 1 nonenveloped, icosahedral capsid that is 26 nm in diameter [3]. The major capsid protein, VP2, is able to selfassemble into empty capsids alone, known as virus-like particles (VLP), which is a major antigen to induce neutralizing antibodies [6]. The VP3 protein is generated from the cleavage of VP2 at approximately 25 amino acids from the N-terminal [7]

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Conclusion