Designing and evaluation of ELISA kit based on preparing antibodies against Apple stem grooving virus coat protein gene expressed in Escherichia coli

Goal: 

production of antibodies against the coat protein of Apple stem grooving virus and their application in diagnostic assays and biosensor design represents a crucial strategy for effective plant virus detection. ASGV is a significant pathogen affecting pome fruit trees. The objective of this study was to express the coat protein gene of ASGV in E. coli, generate antibodies against the expressed protein, and assess their effectiveness in diagnostic assays.

In the PCR, we successfully amplified a 714 bp fragment corresponding to the complete coding region of the ASGV coat protein gene. The amplified fragment was then cloned into the pTG19 vector. Subsequently, the desired fragment was subcloned into the pET28a (+) expression vector using BamHI and EcoRI restriction enzymes. The resulting construct was then introduced into E. coli BL21(DE3) cells for gene expression. To determine the optimal conditions for protein expression, the transformed cells were induced with one mM IPTG for various durations (3, 4, 6, and 16 hours). The expression of the protein was confirmed through SDS-PAGE electrophoresis and western blot analysis. Following the purification of the expressed protein, it was utilized as an antigen for immunizing rabbits. Immunoglobulins (IgGs) were subsequently purified from the rabbit serum, and some of them were employed for conjugate production. The efficacy of the conjugates was evaluated in serological assays.

Sequencing analysis of the amplified fragments conclusively verified their correspondence to the ASGV coat protein gene. Moreover, PCR and enzymatic digestion of the resulting clone provided further evidence of the successful construction of pET28-ASGV-CP. Comprehensive sequence analysis of the constructed plasmid in both directions confirmed the accurate insertion of the coat protein gene into the expression vector, while also confirming the absence of any nucleotide mutations. Following optimization, the expression of the ASGV coat protein was successfully achieved, resulting in an approximate size of 27 kDa. This confirmation was attained through SDS-PAGE electrophoresis and subsequent western blotting, conducted four hours after induction. The direct, indirect, and dot-blot assays were performed to assess the efficiency of the conjugate. The results indicated that the optimal concentration of the conjugate was approximately 1:1000.

The generated and conjugated antibodies exhibit suitable titers relative to the antigen concentration and demonstrate specificity and effectiveness in the detection and identification of Apple stem grooving virus (ASGV). These antibodies can be utilized for various serological diagnostic kits, including ELISA, offering valuable applications in virus detection and identification.