title: Losac, the first hemolin that exhibits procogulant activity through selective factor X proteolytic activation.
abstract: Envenoming by the contact of human skin with Lonomia obliqua caterpillars promotes a hemorrhagic syndrome characterized by a consumptive coagulopathy. Losac (Lonomia obliqua Stuart factor activator) is a component of the bristle of L. obliqua that is probably partially responsible for the observed syndrome because it activates factor X and is recognized by an effective antilonomic serum. Here we unveil the proteolytic activity of Losac and demonstrate the feasibility of its recombinant production. On the other hand, Losac has no homology to known proteases, but it can be inhibited by PMSF, a serine protease inhibitor. Instead, it shows closer homology to members of the hemolin family of proteins, a group of cell adhesion molecules. The recombinant protein (rLosac) shortened the coagulation time of normal and deficient plasmas, whereas it was ineffective in factor X-deficient plasma unless reconstituted with this protein. rLosac was able to activate factor X in a dose- and time-dependent manner but not γ-carboxyglutamic acid domainless factor X. Moreover, phospholipids and calcium ions increased rLosac activity. Also, rLosac had no effect on fibrin or fibrinogen, indicating its specificity for blood coagulation activation. Linear double reciprocal plots indicate that rLosac follows a Michaelis-Menten kinetics. Cleavage of factor X by rLosac resulted in fragments that are compatible with those generated by RVV-X (a well known factor X activator). Together, our results validate Losac as the first protein from the hemolin family exhibiting procoagulant activity through selective proteolysis on coagulation factor X.
authors.affiliation: Laboratório de Bioquímica e Biofísica, Instituto Butantan, São Paulo, SP CEP 05503-900, Brazil.
authors.forename: Miryam Paola
authors.initials: MP
authors.lastname: Alvarez-Flores
authors.forename: Daniel
authors.initials: D
authors.lastname: Furlin
authors.forename: Oscar H P
authors.initials: OH
authors.lastname: Ramos
authors.forename: Andrea
authors.initials: A
authors.lastname: Balan
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Konno
authors.forename: Ana Marisa
authors.initials: AM
authors.lastname: Chudzinski-Tavassi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001777:Blood Coagulation / Q000187:drug effects; D003198:Computer Simulation; D003546:Cysteine Endopeptidases / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D005170:Factor X / Q000378:metabolism; D015951:Factor Xa / Q000378:metabolism; D007136:Immunoglobulins / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D019476:Insect Proteins / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009036:Moths / Q000235:genetics* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics* / Q000378:metabolism* / Q000494:pharmacology; D010447:Peptide Hydrolases / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology
chemical_list: D007136:Immunoglobulins; D019476:Insect Proteins; D009363:Neoplasm Proteins; D011994:Recombinant Proteins; C066846:hemolin; D005170:Factor X; C557790:Losac protein, Lonomia obliqua; D010447:Peptide Hydrolases; D015951:Factor Xa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant