Cloning, purification, crystallization and preliminary X-ray studies of human α₁-microglobulin

α₁-Microglobulin (α₁m) is one of the phylogenetically most widespread lipocalins and is distributed in various organs and tissues, including liver, heart, eye, kidney, brain, lung, pancreas and skeletal muscle. α₁m has been found to exert multifarious functions, including interacting with IgA, albumin and prothrombin, binding strongly to haem and exhibiting reductase activity. Nevertheless, little structural information is available regarding these functions of α₁m. Since determination of three-dimensional structure is a powerful means of functional characterization, X-ray crystallography was used to accomplish this task. Here, the expression, purification, crystallization and preliminary crystallographic analysis of human α₁m are reported. The crystal belonged to space group P4₃, with unit-cell parameters a = b = 36.45, c = 112.68 Å, and diffracted to a resolution of 2.0 Å. The crystals are most likely to contain one molecule in the asymmetric unit, with a V_M value of 1.63 ų Da⁻¹.