Abstract
Foot-and-mouth disease virus (FMDV), the most acid-unstable virus among picornaviruses, tends to disassemble into pentamers at pH values slightly below neutrality. However, the structural integrity of intact virion is one of the most important factors that influence the induction of a protective antibody response. Thus, improving the acid stability of FMDV is required for the efficacy of vaccine preparations. According to the previous studies, a single substitution or double amino acid substitutions (VP1 N17D, VP2 H145Y, VP2 D86H, VP3 H142D, VP3 H142G, and VP1 N17D + VP2 H145Y) in the capsid were introduced into the full-length infectious clone of type O FMDV vaccine strain O/HN/CHN/93 to develop seed FMDV with improved acid stability. After the transfection into BSR/T7 cells of constructed plasmids, substitution VP1 N17D or VP2 D86H resulted in viable and genetically stable FMDVs, respectively. However, substitution VP2 H145Y or VP1 N17D + VP2 H145Y showed reverse mutation and additional mutations, and substitution VP3 H141G or VP3 H141D prevented viral viability. We found that substitution VP1 N17D or VP2 D86H could confer increased acid resistance, alkali stability, and thermostability on FMDV O/HN/CHN/93, whereas substitution VP1 N17D was observed to lead to a decreased replication ability in BHK-21 cells and mildly impaired virulence in suckling mice. In contrast, substitution VP2 D86H had no negative effect on viral infectivity. These results indicated that the mutant rD86H carrying substitution VP2 D86H firstly reported by us could be more adequate for the development of inactivated FMD vaccines with enhanced acid stability.
Highlights
Foot-and-mouth disease (FMD) is a highly infectious vesicular disease of domestic and wild cloven-hoofed animals
Diverse amino acid substitutions responsible for the acid sensitivity phenotype of FMD virus (FMDV) have been reported recently (Xie et al 2019; Yuan et al 2017). Based on those previous findings, to develop acid-stable inactivated vaccines, a panel of substitutions (VP1 N17D, VP2 H145Y, VP2 D86H, VP3 H141D, VP3 H141G, and VP1 N17D/VP2 H145Y) were introduced into infectious cDNA clone pOFS which contained the complete sequence of O/HN/CHN/93
The nearly isosteric substitution VP1 N17D, which is located at the internal region of capsid and close to but not at the inter-pentamer interfaces, has been screened out among different FMDV serotypes
Summary
Foot-and-mouth disease (FMD) is a highly infectious vesicular disease of domestic and wild cloven-hoofed animals. Among all members in the family of Picornaviridae, the FMDV particle is highly acid labile due to the rapid dissociation of capsid into pentameric subunits at pH slightly below neutrality (Newman et al 1973). This acid sensitivity property of FMDV is needed for the uncoating activity in the early endosome of host cell, but during the process of vaccine preparation and storage, the acid stability of virion is demanded (Huotari and Helenius 2011; O'Donnell et al 2005). These interactions are affected by the alteration of pH and temperature in the environment, leading to the dissociation of the capsid (Caridi et al 2015; Curry et al 1995; Martin-Acebes et al 2010; Mateo et al 2008; Rincon et al 2014; van Vlijmen et al 1998)
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