A kringle-containing protease with plasminogen-like activity in the basal chordate Branchiostoma belcheri.
Plg (plasminogen), a member of the serine protease superfamily, is a key component constituting the fibrinolytic system, and its evolutionary origin remains unknown during the course of animal evolution. In the present study, we isolated a cDNA, designated BbPlgl, encoding a kringle-containing protease with plasminogen-like activity from the basal chordate Branchiostoma belcheri. The deduced protein, BbPlgl, consisted of 430 amino acids, which is structurally characterized by the presence of an N-terminal signal peptide of 16 amino acids, 2 kringle domains with a Lys-binding site structure, a serine protease domain with the putative tPA (tissue plasminogen activator)-cleavage site (between Arg297 and Val298), the catalytic triad His237-Asp288-Ser379 expected for protease function, and a potential N-linked glycosylation site, all characteristic of Plgs. Besides, the recombinant refolded BbPlgl was readily activated by human uPA (urokinase plasminogen activator), and exhibited Plg-like activity. BbPlgl was also able to auto-activate at neutral and alkaline pH at 4 degrees C without the addition of uPA, and the activation was accelerated by addition of human uPA. These results demonstrate that BbPlgl is a novel member of the Plg family, with a domain structure of K-K-SP (kringle-kringle-serine protease) lacking the PAN domain, pushing the evolutionary origin of Plg to the protochordate. In addition, BbPlgl displays a tissue-specific expression pattern in B. belcheri, with the most abundant expression in the hepatic caecum and hind-gut, agreeing with the notion that the hepatic caecum of amphioxus is the precursor of the vertebrate liver.
Liu
Mingying
M
Department of Marine Biology, Ocean University of China, Qingdao 266003, China.
Zhang
Shicui
S
D000595:Amino Acid Sequence; D000818:Animals; D002432:Cecum / Q000378:metabolism; D043344:Chordata / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D018082:Kringles / Q000235:genetics; D008099:Liver / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010958:Plasminogen / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
D010958:Plasminogen; D012697:Serine Endopeptidases