Purification and biochemical characterisation of a novel protease streblin

A serine protease, streblin, was purified 4.6-fold with 75% recovery from the latex of a plant, Streblus asper. This is the first report of identification and purification of a serine protease from the genus Streblus of the Moraceae family. Streblin, has a molecular mass of 64 kDa and the extinction coefficient (ϵ2801%) is 5.29. Streblin is a basic protein with pI value of 9.2 that acts optimally at pH 9.0; such optimum activity at high pH has not been reported for most of the isolated plant serine proteases and the enzyme is stable over a wide range of pH (3.0–12.5). The enzyme is also thermostable, retaining complete activity at 15–85 °C and acts optimally at 65 °C. Furthermore, it is highly stable in the presence of various denaturants in which SDS resistance is the most striking property of the purified enzyme. Streblin strongly coagulated skimmed milk. Easy availability of the latex, simple purification procedures, high stability of streblin against pH, or autodigestion, and under various conditions make the enzyme a good system for exploring the biophysical chemistry of proteases. In addition to its high milk-clotting ability, it could be used in the cheese industry, as well as other food and biotechnological industries.