Background

Brown snakes (Pseudonaja textilis) and Taipans (Oxyuranus scutellatus) inhabiting the Australian continent are considered some of the most lethal reptiles on Earth. When the venom of these Elapidae snakes is injected into prey's blood vessels, the body's coagulation system collapses rapidly, leading to disseminated intravascular coagulation. This process causes blood to clot uncontrollably within the vessels, resulting in myocardial infarction or acute stroke. As systemic coagulation factors are rapidly depleted, it ultimately leads to fatal internal bleeding.

How such a sophisticated and potent blood-clotting toxin evolved has long been a question. In evolutionary biology, Susumu Ohno's hypothesis—that a gene first duplicates into two, and then one copy acquires a new function through mutation—was widely accepted as the standard. However, the resolution of existing genomic analyses was insufficient to reveal the subtle phylogenetic differences between glandular tissue and venom gland tissue.

Key Findings

Researchers precisely compared the high-resolution whole genomes and venom gland transcriptomes of 28 species of Australian elapid snakes to reconstruct the molecular evolution of prothrombin complex-like toxins. The analysis revealed that blood-clotting venoms did not arise from a single event, but rather resulted from the precise interplay of two independent genetic pathways.

The first pathway involves the novel recruitment of normal endogenous coagulation factors. Genes for blood coagulation Factor X (FX), Factor V (FV), and Factor VII (FVII), which were previously secreted from the liver into the bloodstream, began to be expressed heterotopically in the venom gland tissue. Crucially, this functional variation was triggered even in a single-copy state prior to gene duplication. As the missecreted coagulation proteins in the venom gland increased hunting success rates, strong natural selection acted, followed by segmental duplication that firmly established a venom gland-specific gene locus. Subsequent gain-of-function mutations remodeled the protein structure so that the enzymes remain in a constitutively active state without the need for calcium ions or cell membrane cofactors.

The second pathway is the functional shift of neurotoxic genes already present in the venom glands. Group I phospholipase A2 (PLA2), which previously acted via membrane disruption, and Kunitz-type toxins, which acted as cellular enzyme inhibitors, underwent neofunctionalization to become facilitators that trigger platelet aggregation. When the core enzymes derived from liver proteins combined with cofactors modified from neurotoxins, a multi-molecular toxin cocktail exhibiting unprecedented coagulation activity was finally formed.

Significance and Outlook

This study overturns a long-standing dogma in molecular evolution by demonstrating that tissue-specific expression shifts and single-gene mutations can precede gene duplication when a new biochemical weapon emerges. It is evaluated as an achievement that perfectly reconstructs the step-by-step molecular narrative of how metabolic regulatory genes transform into lethal weapons.

The stereochemical mechanism of toxins that maintain maximized enzymatic activity by escaping normal regulation provides fresh inspiration for artificial protein engineering and the design of next-generation hemostatic formulations. However, this is because it has been pointed out that physicochemical validation of dynamics through ancestral sequence reconstruction must be fully completed following computational biological phylogenetic reconstruction. Ensuring safety through molecular control to restrict the ultra-fast solidification effect to specific areas is also a key challenge that researchers must address in the future.