Cloning, expression, purification and in silico analysis of n-terminal domain of pneumococcal surface protein a from all six clades

Streptococcus pneumoniae (or pneumococci) is the leading cause of life-endangering diseases like pneumonia and septicemia. Antigenically variable Pneumococcal surface protein A (PspA) is one of the better defined pneumococcal virulence factors. Based on its sequence PspA has been classified into three families and six clades. Here, we repot cloning, expression and purification of all six clades of PspA (extracellular domain only). Bioinformatics analysis suggested that N-terminal fragments of PspA were highly variable at amino acid level while evolutionary conserved at secondary structural level. Study showed that the all PspA have very high content of α-helical structure and no other structure have been observed except random coil. The mice immunized with recombinant PspA fragments elicited very high antibody titers and confirmed the immunogenicity of PspA. Hence, our results would help to identify the cross-reactivity of antibody and structurally correlate across the clade of PspA.