Purification, crystallization and preliminary X‐ray analysis of human mannose‐binding lectin‐associated serine protease‐1 (MASP‐1) catalytic region
MASP‐1, a multidomain serine protease, is a component of the lectin pathway of complement. Its precise function is unknown, although it seems to enhance the complement‐activating capacity of MASP‐2, a related enzyme. MASP‐1 has also been implicated as playing a role in blood coagulation. It is mostly found associated with mannose‐binding lectin (MBL) and ficolins. Early attempts to crystallize MASP‐1 failed because of the inhomogeneity of the purified material. MASP‐1 was shown by acidic nondenaturing PAGE to be composed of differently charged species, which are most likely to be the products of deamidation occurring during the refolding procedure. Sequential cation‐exchange and anion‐exchange chromatography resulted in a homogeneous material, which was successfully crystallized. The best crystal diffracted to 2.55 Å resolution and belonged to space group P212121, with unit‐cell parameters a = 68.4, b = 70.4, c = 121.4 Å. The crystal structure of MASP‐1 may help in understanding the function of this mysterious serine protease.
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