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Mosquito salivary glands secrete a number of proteins that inhibit mammalian hemostasis and facilitate blood feeding. We have isolated the protein product and corresponding cDNA of a gene designated Anticoagulant-factor Xa (AFXa), that encodes the factor Xa (FXa)-directed anticoagulant of the yellow fever mosquito, Aedes aegypti. The protein was purified partially by cation exchange chromatography and shown by enzyme activity profiles and SDS-polyacrylamide gel electrophoresis analysis to have an Mr = 54, 000. The protein was purified further by preparative SDS-polyacrylamide gel electrophoresis and subjected to internal protein sequencing, and the sequence of five peptides was determined. Degenerate oligonucleotides were designed based on three of the peptide sequences, and these were used to screen an adult female salivary gland cDNA library from A. aegypti. A 1.8-kilobase pair cDNA was isolated and shown to encode a 415-amino acid conceptual translation product with a predicted molecular mass of 47.8 kDa that contains the five sequenced peptides. Hydrophobicity analysis predicts a 19-amino acid signal peptide typical for secreted proteins. Northern analysis demonstrated that AFXa is expressed only in female salivary glands. Baculovirus-expressed AFXa protein has the appropriate size and expected FXa-directed anticoagulant activity. Analysis of the primary amino acid sequence shows that the AFXa gene product has similarities to the serpin superfamily of serine protease inhibitors and may represent a novel, highly diverged member of this family.

Original publication




Journal article


J Biol Chem

Publication Date





20802 - 20809


Aedes, Amino Acid Sequence, Animals, Baculoviridae, Base Sequence, DNA, Complementary, Disease Vectors, Female, Insect Proteins, Molecular Sequence Data, Open Reading Frames, RNA, Messenger, Recombinant Proteins, Salivary Proteins and Peptides, Sequence Homology, Amino Acid, Serpins, Yellow Fever