Protein expression and preliminary crystallographic analysis of amino-terminal fragment of urokinase-type plasminogen activator

The amino-terminal fragment (ATF, Ser1-Glu143) of urokinase-type plasminogen activator (uPA) is responsible for some important functions of uPA, such as receptor binding and chemotactic activity. To dissect the function and structure-activity relationship of ATF, recombinant human ATF was expressed in Pichia pastoris system at a yield of about 30 mg/L. The recombinant ATF was captured by a cation exchange column, further purified up to 99% purity by a gel filtration column, and characterized in terms of its receptor binding capability. The purified ATF was then crystallized by the method of sitting-drop vapor diffusion with magnesium sulfate as the precipitating agent at 298 K. The crystals belong to space group P1 with unit cell dimensions of a = 47.5 Å, b = 64.7 Å, c = 65.4 Å, α = 71.6°, β = 92.1°, γ = 84.0°.