Molecular cloning, expression, purification and characterization of truncated forms of human plasminogen in Pichia pastoris expression system

Human plasminogen (HPG), which contains a catalytic domain together with five kringle domains, can be readily purified from blood plasma by chromatography on lysine-agarose. However, its truncated derivatives are needed for various important therapeutic applications. The proteolytic digestion of plasminogen in vitro yields several low molecular weight variants viz. the kringle-less catalytic domain, known as micro-plasminogen (microPG), or miniplasminogen (miniPG), which consists of microPG with an intact kringle-5 domain. However, this method is extremely cumbersome due to a requirement of stringent control on the limited proteolysis process, which often leads to very poor recoveries of the desired product/s, apart from the potentially serious safety-regulatory issues associated with blood-derived therapeutic products. Here, we describe the high-level secretory expression of these important plasminogen derivatives employing Pichia pastoris as the expression host with an engineered alpha-mating factor signal sequence. The purified proteins were found to be functionally comparable with human blood plasminogen-derived ‘native’ forms in terms of their N-terminal amino acid sequences and molecular mass, as well as functional properties. This study paves the way for the facile large-scale production of recombinant human plasminogen derivatives required for thrombolytic and other life-saver therapies.