Identification and characterisation of Kunitz-type plasma kallikrein inhibitors unique to Oxyuranus sp. snake venoms

As part of a wider study on Australian snake venom components, we have identified and characterised Kunitz-type protease inhibitors from the venoms of Oxyuranus scutellatus and Oxyuranus microlepidotus (Australian taipans) with plasma kallikrein inhibitory activity. Each inhibitor had a mass of 7 kDa and was purified from the venom as part of a protein complex. Mass spectrometry and N-terminal sequencing was employed to obtain amino acid sequence information for each inhibitor and a recombinant form of the O. scutellatus inhibitor, termed TSPI, was subsequently expressed and purified. TSPI was investigated for inhibition against a panel of 12 enzymes involved in haemostasis and estimates of the Ki value determined for each enzyme. TSPI was found to be a broad spectrum inhibitor with most potent inhibitory activity observed against plasma kallikrein that corresponded to a Ki of 0.057 ± 0.019 nM. TSPI also inhibited fibrinolysis in whole blood and prolonged the intrinsic clotting time. These inhibitors are also unique in that they appear to be found only in Oxyuranus sp. venoms. ► Characterisation of Kunitz inhibitor from O. scutellatus snake venom. ► Identification and partial characterisation of a new Kunitz inhibitor from O. microlepidotus venom. ► O. scutellatus taicatoxin serine protease inhibitor is a potent inhibitor of plasma kallikrein and other enzymes. ► This Kunitz inhibitor family is unique to Oxyuranus sp. snake venoms