Cloning and expression of gene fragment IgA-binding protein of group B streptococci

Different fragments of the bac gene coding for the IgA-binding protein were cloned, sequenced and expressed in E. coli. Cloning was accomplished after amplification of different parts of the gene by PCR The 15-kb fragment of the gene was cloned using plasmid pBluescript. This fragment coded for the 45-kDa protein with the stable expression of IgA binding. In order to verif y the exact location of the IgA-binding domain two smaller plasmids were co nstructed. Both plasmids were prepared using pQE30 (31, 32) expression vect ors from Qiagen. The plasmids carried 245 and 123 bp bac gene fragments enc oding 14- and 7-kDa proteins. These proteins together with the 20-amino-aci d oligopeptide ITNEDKDSMLKKIEDINRQA were tested for IgA binding. Only the 1 4-kDa protein was able to bind IgA. This protein was used for rabbit immuni zation and found to be immunogenic. The data obtained lead to the conclusio n that there is a lower limit in the size of recombinant IgA-binding protei ns that can be utilized for anti-GBS vaccination.