Molecular cloning and sequence analysis of alboaggregin B

Abstract

Green pit viper (Trimeresurus albolabris) venom contains a variety of C-type lectin-like proteins (CLPs) causing platelet aggregation and consumptive thrombocytopenia in biting victims. Alboaggregin B (AL-B), a heterodimeric glycoprotein (Gp) Ib-binding protein, was purified from the venom, but there is no reported cDNA sequence and the platelet agglutination mechanism is poorly understood. The full-length AL-B β clone was obtained from T. albolabris venom gland cDNA library. AL-B α was, later, derived using 3′-RACE based on the conserved sequence. In this study, purified AL-B dimer agglutinated human platelets with the EC₅₀ of 180 nM and was completely inhibited by anti GpIb antibody. MALDI ToF mass spectroscopy found no glycosylation. The peptide mass fingerprints were matched with deduced amino acid sequences of cloned genes. AL-B α and β contained 156 and 146 amino acid, respectively, including 23-residue signal peptides. AL-B β showed the conserved hydrophilic patches, putative sites for GpIb binding. Furthermore, there was another conserved motif (SRTY) exclusively in platelet-agglutinating AL-B, TSV-GPIb-BP and Mamushigin. We propose that these three CLPs may function as bivalent adhesive proteins linking two GpIb molecules on adjacent platelets.

• Snake venom
• C-type lectin
• alboaggregin B
• glycoprotein Ib
• platelet agglutination