CysP is responsible for the cIgG cleavage caused by M. synoviae and probably, by M. gallisepticum. M. synoviae strains, including the type strain WVU 1853, revealed 39-bp deletion in the 3’ end of the cysP gene while all M. gallisepticum strains showed deletion of 66 bp. Both species M. synoviae and M. gallisepticum showed the capability to digest chicken IgG into fragments corresponding to Fab of ~ 45 kDa and Fc of IgG heavy chain (~ 60 kDa). We changed 8 TGA codons to TGG in the cysP gene of M. synoviae ULB 925 and expressed a recombinant CysP, which cleaved cIgG into Fab and Fc fragments.
The study shows that M. synoviae strains lacking NEAC did not express NanH neuraminidase detectable. In M. synoviae strains ULB 925 and ULB 9122, which lacked NEAC and functional NanH, deletions of a single adenine in different nanH gene regions of each strain created translational frameshifts resulting in TAA (UAA) stop codons and premature termination of translation. ULB 925 and ULB 9122 with such nanH mutations did not desialylate reference fetuin and transferrin or chicken glycoproteins that M. synoviae strains with NEAC efficiently desialylated.