Figure 2

GtxA is a novel RTX-like protein with an unusual domain organization. Schematic presentation of the domain organization of GtxA from G. anatis biovar haemolytica strain 12656–12 [RefSeq:WP_013746567] compared to the typical domain organization of RTX toxins represented by HlyA from E. coli [PRF:225074]. HlyA has 34% coverage and 29% identity with GtxA. Regions of homology are shown with dotted lines. The GtxA toxin is comprised of 2038 amino acids (aa). In the N-terminal part of GtxA (approximately aa 1 – 950), two overlapping regions with weak homology to a membrane protein with unknown function (COG1511) is present. The remaining C-terminal part of GtxA has homology to HlyA by having a RTX N-terminal domain (pfam02382), the Ca²⁺-binding repeats (COG2931) and a domain classified as peptidase M10 serralysin C terminal (pfam08548). GtxA also contains the lysine residues, Lys1484 and Lys1607, required for activation of the toxin by acetylation by GtxC. The homologue lysine residues in HlyA are found at Lys564 and Lys690. In addition to the described domains, HlyA also contains a RTX C-terminal domain (pfam08339). Domains were identified using NCBI conserved domain search with default settings.