Whitby F G, Phillips J D, Kushner J P, Hill C P
Department of Biochemistry, University of Utah School of Medicine, 50 N.Medical Drive, Salt Lake City, UT 84132, USA.
EMBO J. 1998 May 1;17(9):2463-71. doi: 10.1093/emboj/17.9.2463.
Uroporphyrinogen decarboxylase (URO-D) catalyzes the fifth step in the heme biosynthetic pathway, converting uroporphyrinogen to coproporphyrinogen by decarboxylating the four acetate side chains of the substrate. This activity is essential in all organisms, and subnormal activity of URO-D leads to the most common form of porphyria in humans, porphyria cutanea tarda (PCT). We have determined the crystal structure of recombinant human URO-D at 1.60 A resolution. The 40.8 kDa protein is comprised of a single domain containing a (beta/alpha)8-barrel with a deep active site cleft formed by loops at the C-terminal ends of the barrel strands. Many conserved residues cluster at this cleft, including the invariant side chains of Arg37, Arg41 and His339, which probably function in substrate binding, and Asp86, Tyr164 and Ser219, which may function in either binding or catalysis. URO-D is a dimer in solution (Kd = 0.1 microM), and this dimer also appears to be formed in the crystal. Assembly of the dimer juxtaposes the active site clefts of the monomers, suggesting a functionally important interaction between the catalytic centers.
尿卟啉原脱羧酶（URO-D）催化血红素生物合成途径中的第五步反应，通过使底物的四个乙酸侧链脱羧，将尿卟啉原转化为粪卟啉原。这种活性在所有生物体中都是必不可少的，而URO-D活性低于正常水平会导致人类最常见的卟啉症——迟发性皮肤卟啉症（PCT）。我们已经确定了重组人URO-D的晶体结构，分辨率为1.60 Å。这种40.8 kDa的蛋白质由一个单一结构域组成，该结构域包含一个（β/α）8桶状结构，在桶状链C末端的环形成一个深的活性位点裂隙。许多保守残基聚集在这个裂隙处，包括Arg37、Arg41和His339的不变侧链，它们可能在底物结合中起作用，以及Asp86、Tyr164和Ser219，它们可能在结合或催化中起作用。URO-D在溶液中是二聚体（Kd = 0.1 μM），并且这种二聚体在晶体中似乎也会形成。二聚体的组装使单体的活性位点裂隙并列，表明催化中心之间存在功能上重要的相互作用。
