A truncated form of mannose-binding lectin-associated serine protease (MASP)-2 expressed by alternative polyadenylation is a component of the lectin complement pathway.
The lectin complement pathway is initiated by binding of mannose-binding lectin (MBL) and MBL-associated serine protease (MASP) to carbohydrates. In the human lectin pathway, MASP-1 and MASP-2 are involved in the proteolysis of C4, C2 and C3. Here we report that the human MBL-MASP complex contains a new 22 kDa protein [small MBL-associated protein (sMAP)] bound to MASP-1. Analysis of the nucleotide sequence of sMAP cDNA revealed that it is a truncated form of MASP-2, consisting of the first two domains (i.e. the first internal repeat and the epidermal growth factor-like domain) with four different C-terminal amino acids. sMAP mRNAs are expressed in liver by alternative polyadenylation of the MASP-2 gene, in which a sMAP-specific exon containing an in-frame stop codon and a polyadenylation signal is used. The involvement of sMAP in the MBL-MASP complex suggests that the activation mechanism of the lectin pathway is more complicated than that of the classical pathway.
D000595:Amino Acid Sequence; D001483:Base Sequence; D002118:Calcium / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics*; D003172:Complement C1 / Q000502:physiology*; D018076:DNA, Complementary / Q000737:chemistry; D005091:Exons; D006801:Humans; D037102:Lectins / Q000502:physiology*; D037241:Mannose-Binding Lectins; D050606:Mannose-Binding Protein-Associated Serine Proteases; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000235:genetics*