Abstract
Venom 5’-nucleotidases (V5NTD) are widely represented in venomous snakes. Its biological function was less extensively investigated in the past cobra envenomation research owing to its scarcity in cobra venom (0.38% of Taiwan cobra venom proteins). In recent studies, it has been implied to conduct anti-coagulation by liberating of extracellular adenosine through purinergic pathways. To understand how V5NTD catalysed AMP, we purified V5NTD from Taiwan cobra (Naja atra) crude venom to determine its 3D structure at 1.9 Å by X-ray crystallography. By structural analysis, we found the crystal structure of V5NTD is similar to its human homologous protein, ecto-5’-nucleotidase (e5NT, a.k.a. CD73), an ecto-enzyme known for its immune regulatory activity. Through decoding V5NTD protein sequence from Naja atra venom gland cDNA, we use molecular replacement to exhibit the homodimeric isoform consists of monomers with 60 kD. This research not only provides a method to purify V5NTD from crude cobra venom, but also build the first native vertebrate ecto-5’-nucleotidase structure which elucidates the ionic-interaction in V5NTD dimerization interface and different glycosylation sites from human CD73. This molecular structural-based study can assist to clarify the biological functions of V5NTD after envenomation.