Designing multi-epitope subunit vaccine for ocular trachoma infection using Chlamydia trachomatis polymorphic membrane proteins G

Abstract

Chlamydia trachomatis serovars A, B, Ba and C are bacteria serovars responsible for the blinding disease trachoma, the infection affects the upper tarsal conjunctiva of the eye. Repeated infection occurs among people in endemic areas throughout childhood which may later lead to blindness at adulthood. Chlamydia trachomatis contains a highly conserved surface glycoprotein, the polymorphic membrane protein which are surface antigens and are target for neutralizing antibodies as they are strongly immunogenic hence elicit proinflammatory response. It is suggested that they may be virulence by modulating inflammation and adherence to host cell, therefore one can argue that PMPs may be important in host-cell invasion as a virulence factor; this fact makes it a good entrant for Chlamydia trachomatis vaccine design.In this study a combination of bioinformatics and immunoinformatics methods and tools were applied to design multi-epitope subunit vaccines using Chlamydia trachomatis polymorphic membrane protein G (PMPG). The vaccine candidate was constructed using suitable linkers to link the CTL epitopes, HTC epitopes and adjuvant together, this constructed vaccine candidate was appraised for its antigenic and allergenic properties, the physicochemical parameters which include the molecular formula, theoretical isoelectric point (pI), molecular weight, half-life, instability index, solubility score, GRAVY and aliphatic index were also predicted. The vaccine secondary structure was predicted to evaluate the properties of the secondary structure of the vaccine such as the helices, sheets and coils. The tertiary structure was also predicted, refined and validated using data like Ramachandran plot and Z-score. Disulfide engineering was executed in regions having high mobility in order to improve the protein stability of the candidate vaccine, from this, three pairs of amino acid residues GLY112-THR135, TYR137-ARG139 and THR144-ASN147 were finalized based on their chi3 and B-factor value. Codon adaptation carried out revealed that the vaccine candidate sequence has a GC-content of 53.75% and codon adaptation index of 1.0. In silico cloning was also carried out to determine the vector and cloning site suitable for overproduction of the vaccine protein for large scale production process. To determine the complex stability and binding free energy of the vaccine candidate, molecular docking was performed using the vaccine protein as ligand while TLR-2 and TLR-4 were the receptors. The lowest binding energy for the vaccine-TLR4 complex was −1626.7 and −1305.1 for the vaccine-TLR2 complex. Dynamic simulation provided predictions such as eigenvalue of 5.277774 × 10−06 for TLR-4 receptor and 7.403984 × 10−06 for TLR-2 receptor. From results obtained from the various predictions and validations, it can be concluded that the candidate vaccine will be capable of inducing anti-inflammatory immunity which may be able to prevent Chlamydia trachomatis invasion among human hosts.