‘Pergularain e I’ – a plant cysteine protease with thrombin-like activity from Pergularia extensa latex

Pergularain e I, a cysteine protease with thrombin-like activity, was purified by ion exchange chromatography from the latex of Pergularia extensa. Its homogeneity was characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS–PAGE), native PAGE and reverse-phase high-performance liquid chromatography (RP-HPLC). The molecular mass of pergularain e I by matrix-assisted laser desorption ionization–time of flight (MALDI–TOF) was found to be 23.356 kDa and the N-terminal sequence is L–P–H–D–V–E. Pergularain e I is a glycoprotein containing ∼ 20% of carbohydrate. Pergularain e I constituted 6.7% of the total protein with a specific activity of 9.5 units/mg/min with a 2.11-fold increased purity. Proteolytic activity of the pergularain e I was completely inhibited by iodoacetic acid (IAA). Pergularain e I exhibited procoagulant activity with citrated plasma and fibrinogen similar to thrombin. Pergularain e I increases the absorbance of fibrinogen solution in concentration-dependant and time-dependant manner. At 10 μg concentration, an absorbance of 0.48 was reached within 10 min of incubation time. Similar absorbance was observed when 0.2 NIH units of thrombin were used. Thrombin-like activity of pergularain e I is because of the selective hydrolysis of Aα and Bβ chains of fibrinogen and γ-chain was observed to be insusceptible to hydrolysis. Molecular masses of the two peptide fragments released from fibrinogen due to the hydrolysis by pergularain e I at 5-min incubation time were found to be 1537.21 and 1553.29 and were in close agreement with the molecular masses of 16 amino acid sequence of fibrinopeptide A and 14 amino acid sequence of fibrinopeptide B, respectively. Prolonged fibrinogen–pergularain e I incubation releases additional peptides and their sequence comparison of molecular masses of the released peptides suggested that pergularain e I hydrolyzes specifically after arginine residues.