The organisation and conservation of the mannan-binding lectin (MBL) associated serine protease-3 (MASP-3) in mammals, amphibia, reptiles and bony fish

Mannan binding lectin associated serine protease (MASP) are found associated with Mannan binding lectin (MBL) and ficolin, two alternative recognition molecules involved in activation of the lectin arm of the complement cascade. MBL and ficolin (H-ficolin, L-ficolin and M-ficolin) recognise carbohydrate moieties on the surface of pathogens; a resulting conformational change in the recognition molecule converts the associated MASP proenzyme to its active form. MBL-MASP complexes play an essential role in the innate immune response in the period before an epitope specific adaptive antibody driven solution is found, to date there are three known MASP. MASP and MASP-like proteins generate much interest due to their unique position in the activation apparatus of the complement pathway. Being the point of the first proteolytic cleavage for subsequent cleavage events, MASPs are an ideal point to apply a brake to any spurious activation leading to disease. The aim of this study is to further the knowledge of MASP-3 role in the lectin pathway and establish its connection with other members of the MASP family of proteins. MASP-3 is the most recently characterised mannan binding lectin associated serine protease, here is presented the cloning, characterisation and recombinant expression of this novel complement serine protease in a number of mammalian and non-mammalian species. MASP-3 demonstrates a striking degree of sequence conservation between species. MASP-3 is an alternatively spliced transcript of the MASP-1/3 locus; this study identifies in the current sequence database a truncated third alternatively splice transcript in human, rhesus monkey, rat, mouse and porcine species.