Mannan binding lectin serine protease (MASP) plays an essential important role in innate immune response of host, especially in activation of complement system via the lectin and alternative pathways. MASPs family consisted of three distinct proteins (MASP1, MASP2 and MASP3). Therefore, the current study aimed at sequencing the whole gene and analyzing cDNA and molecular structure of MASP3 (MASP1 isoform 2). With 2657 bp and 11 exons, in which the coding region (nt 152-2388) encoded the protein MASP3 with 728 amino acids. cDNA and protein MASP3 among mammalian species (pig, human, cattle and dog) showed a high homology of 87-90 percent and of 92-94 percent, respectively. MASP3 had 27 cysteine residues. Amino acids showing a high percentage in the polypeptide included Ser (8.4 percent), Val (8.1 percent), Leu (8.0 percent), Gly (7.6 percent) and Glu (7.1 percent). With a molecular mass of approximately 81.55 kDa, MASP3 was an assembly of rich-cysteine protein domains such as CUB1 (aa 18-138,2 cysteine), EGF _ CA (aa 139-182,6 cysteine), CUB2 (aa 185-297, 3 cysteine), CCP1 (aa 301-362, 4 cysteine), CCP2 (aa 367-432, 4 cysteine) in N-terminus and Tryp_SPc (aa 449-711, 5 cysteine) in C-terminus. Tryp _ SPc was the largest domain whereas EGF_CA was the smallest. Besides, a signal peptide (aa 1-19), 13 disulfide bonds, 5 N-glycosylation sites, and methionine loop (aa 630-649) were also identified. All this molecular structure of the protein MASP3 was basic to study the role of MASP3 in immune response mechanism for disease resistance in pigs.
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