Structure of two genes encoding parallel prothrombin activators in Tropidechis carinatus snake: gene duplication and recruitment of factor X gene to the venom gland

Abstract

To cite this article: Reza MA, Swarup S, Kini RM. Structure of two genes encoding parallel prothrombin activators in Tropidechis carinatus snake: gene duplication and recruitment of factor X gene to the venom gland J Thromb Haemost 2007; 5: 117-26.Summary. Background: Proteins with new function originate through gene duplication followed by divergence. In nature, occurrence of structurally and functionally similar proteins performing highly diverse physiological roles within an organism is rare. Several Australian elapid snakes have two parallel prothrombin activating systems with distinct physiological roles. For example, in Tropidechis carinatus, trocarin D exists in the venom and acts as toxin, whereas coagulation factor (F) X exists in plasma and plays a role in hemostasis. Results: Here, we show that FX and the trocarin D genes are expressed in a highly tissue-specific manner in T. carinatus. To understand their origin, recruitment and evolution, we determined the complete structure of their genes. Both genes have eight exons with identical exon-intron boundaries. All the introns are 92-99% identical with the exception of intron 1, indicating a recent gene duplication event. The first intron of the trocarin D gene is also nearly identical to that of the FX gene, except for two deletions (255 and 1406 bp) and three insertions (214, 1975, and 2174 bp). The third insertion has a potential scaffold/matrix attached region. The putative promoter of the snake FX gene shares similar cis-elements compared with those of human and murine FX genes. Interestingly, the trocarin D promoter has a 264-bp insertion with core promoter sequences and cis-elements that are known to induce high-level expression. This insertion might be responsible for switching from constitutive expression of the FX gene to inducible expression of trocarin D. Thus, we named this segment as VERSE (Venom Recruitment/Switch Element). Conclusion: To our knowledge, this is the first molecular evidence for the recruitment of a duplicated gene for expression in venom glands by a simple insertion.

Duplication of Coagulation Factor Genes and Evolution of Snake Venom Prothrombin Activators

“…Real-time polymerase chain reaction (RT-PCR) was used to determine the amount of expression of these two closely related proteins in the liver and venom gland. The results indicate that trocarin D is expressed in the venom gland but 437 437 iver_type_1 417 iver_type_2 421 Cat 420 TADFANQVLMKQDFGIVSGFGRTRERGQTSNTLKVVTLPYVDRHTCMLSSNFPITQNMFCAGYNTLPQDACQGDSGGPHITAYRDTHFIT TADFANQVLMKQNFGIVSGFGRTRERGKTSNTLKVVTLPYVDRHTCMLSSNFPITQNMFCAGYDTLPQDACQGDSGGPHITAYRDTHFIT TADFANQVLMKQDFGIVSGFGRIFEKGPKSKTLKVLKVPYVDRHTCMVSSETPITPNMFCAGYDTLPRDACQGDSGGPHTTVYRDTHFIT TADFANQVLMKQDFGIVSGFGGIFGRGPNSKTLKVLKVPYVDRHTCMLSSNFPITPTMFCAGYDTLPQDACQGDSGGPHITAYRDTHFIT TADFANEVLMKQDSGIVSGFGRIQFKQPTSNTLKVITVPYVDRHTCMLSSDFRITQNMFCAGYDTLPQDACQGDSGGPHITAYRDTHFIT T T T (Reza et al 2007). Such differential expression patterns of trocarin D and TrFX strongly support the distinct physiological roles of these two proteins.…”

“…The duplicated FX gene was subsequently modified and "recruited" for expression in the venom gland as a venom prothrombin activator. (Reza et al, 2007).…”

“…However, TLB2 is the primary TATA box which initiates and directs transcription start site (Kwong et al 2009) (Figure 9). (Reza et al, 2007).…”

“…The overlapping promoter regions of trocarin D and TrFX were characterized by comparing them against previously characterized human (Hung et al 2001;Hung and High 1996) and murine (Wilberding and Castellino 2000) FX promoter regions (Reza et al 2007) (Figure 9). Based on these comparisons, four conserved cis-regulatory elements in the trocarin D and TrFX promoter regions were identified ( Figure 9): (i) a CCAAT box (Hung et al 2001;Hung and High 1996;Wilberding and Castellino 2000), (ii) a gut-specific transcription factor GATA-4 binding site (Hung et al 2001), (iii) a liver-specific transcription factor HNF-4 (Hung and High 1996), and (iv) multiple Sp1/Sp3 binding sites (Hung et al 2001).…”

“…The difference in size is explained by three insertions and two deletions in the trocarin D intron 1 region (Reza et al 2007) (Figure 10). Bioinformatics analysis of these insertion/deletion segments reveals that they are novel.…”