Figure 2: Sequence features of cartilaginous fish Hp.

(a) MSA of nurse shark (Gici), little skate (Leer) and small-spotted catshark (Scca) Hp with the two human (Hosa) Hp alleles (Genbank accession numbers; Hp1 NP_005134.1; Hp2 NP_001119574.1) and trout (Onmy) Hp-like (sequence from 9); CCP and serine protease (SP) domains are shaded and the pro-Hp cleavage motif underlined. The cysteines responsible for interchain bonding are marked by dots above the sequence and the unpaired cysteines that facilitate Hp oligomerization in mammals are highlighted in yellow. Cysteine pairs that form disulphide bonds in mammalian Hp are indicated by solid lines above the alignment while additional disulphide bonds predicted in cartilaginous fish Hp are indicated by dashed lines below the alignment. The charged residues important for the electrostatic docking of human Hp oligomers are indicated by +/− above the alignment. The residues which form the active site in other SP domains are indicated by white lettering on black, and the conserved Asp located at the base of the active-site cavity is marked with an asterisk. Residues identified as important in Hp-Hb complex formation [30] in mammals are shaded red, while those important for CD163 binding [32] are shaded blue. (b) Phylogenetic analysis of MASP CCP domains; regardless of the MASP family member or species from which they are derived, the CCP1 and CCP2 domains (shown in blue and red respectively on the structural schematic for a typical MASP family member) segregate into distinct clades. (c) However, both CCP domains in human, cow, shark, and skate Hp fall within the CCP2 group indicating independent domain duplication events in these lineages (marked by stars). Full tree topologies, posterior probabilities, species names, and accession numbers for (a) and (b) are presented in supplemental figures 2b and 2c respectively.