Introduction
Coronaviruses (CoV) are enveloped viruses that have been identified in humans and in several animals (Cui et al., 2019). Currently, six different swine CoV (SCoV) have been described: Transmissible Gastroenteritis Virus (TGEV), Porcine respiratory coronavirus (PRCV), Porcine epidemic diarrhea virus (PEDV), Swine Acute Diarrhea Syndrome Coronavirus (SADS-CoV), Porcine Hemagglutinating Encephalomyelitis Virus (PHEV) and the emergent Porcine Deltacoronavirus (PDCoV) (Zhang, 2016). PDCoV has a positive single-stranded RNA genome with a length of 25 kb approximately. The genome organization is in the following order: 5′ untranslated region (UTR), open reading frame 1a/1b (ORF1a/1b), spike (S), envelope (E), membrane (M), nonstructural protein 6 (NS6), nucleocapsid (N), nonstructural protein 7 (NS7), and 3′ UTR (He et al., 2020; Zhang, 2016).
After the first isolation (HKU15) of PDCoV in China in 2012 (Woo et al., 2012), several reports of detection has been informed both in Asia as in America (Ajayi et al., 2018; Le et al., 2018; Lee et al., 2016; Li et al., 2014; Lorsirigool et al., 2017; Lorsirigool et al., 2016; Perez-Rivera et al., 2019). The pathogenesis of the virus preferentially occurs within the enterocytes of the small intestine, where the virus interacts with its antigens and the cells their receptors facilitating the invasion and proliferation into them (Jung et al., 2016). Damage to the epithelia is traduced in watery diarrhea, dehydration and vomit signs that easily affect piglets with mortality rates of > 40%. (Feng et al., 2020; Niederwerder & Hesse, 2018; Wang et al., 2019). PDCoV frequently co-infect with PEDV, TGEV and, Rotavirus C, increasing the intestinal cell damage and inducing a severe infection (Hu et al., 2015; Song et al., 2015). In this scenario, early and suitable diagnosis is of vital importance.
The M protein is required for the virus assembly process is the most abundant component of the virus envelope which is highly conserved (de Haan & Rottier, 2005; Narayanan et al., 2003; Stadler et al., 2003; Wang et al., 2020; Weiss & Leibowitz, 2011). Also, the M protein promote the production of antibodies with virus-neutralizing activity (Weiss & Leibowitz, 2011). Furthermore, cross-reactivity of PDCoV with antibodies to either PEDV or TGEV M protein has not been previously observed (Chen et al., 2015; Jung et al., 2016; Ma et al., 2015). Therefore, the M protein suits as candidate for induction of specific antibodies and diagnosis of PDCoV detection.
Despite that PDCoV as an emerging coronavirus, little is known about the currently prevalence within the pig population in México. The present study deals with the construction and expression in E. coli of recombinant proteins from a synthetic gene obtained after in silico analysis on 138 sequences of the M protein of PDCoV (r M-PDCoV) previously informed at the GenBank.