Phosphate forms an unusual tripodal complex with the Fe-Mn center of sweet potato purple acid phosphatase
Phosphate forms an unusual tripodal complex with the Fe-Mn center of sweet potato purple acid phosphatase
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DOI：
10.1073/pnas.0407239102
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发表时间：
2005-01-11
影响因子：
11.1
通讯作者：
Guddat, LW
中科院分区：
文献类型：
--
作者：
Schenk, G;Gahan, LR;Guddat, LW
紫酸性磷酸酶（PAPs）是一类双核金属酶，可催化磷酸酯和酸酐的水解。甘薯中的PAP具有独特的，强反铁磁偶联的Fe(III)-Mn（II）中心，与其他PAP不同的是，它对一系列活化和未活化的磷酸酯具有更高的催化效率，对Mn（II）有严格的要求，并且在pH为4.90时存在mu-氧桥。该酶在pH值为4.5时表现出最大的催化效率（k(cat)/ k -m），而其催化速率常数（k(cat)）在接近中性的pH值时达到最大，并且与其他pap相比，其催化参数不依赖于离去基的pK(a)。磷酸盐结合Fe(III)-Mn(II) PAP的晶体结构被确定为2.5埃分辨率（最终无r值为0.256）。红薯、红芸豆和哺乳动物PAPs活性位点的结构比较表明，红薯酶中的几个氨基酸取代可以解释其催化效率提高的原因。磷酸盐分子以一种不寻常的三脚架模式与两个金属离子结合，其中两个磷酸盐氧原子与Fe（III）和Mn（II）结合，第三个氧原子连接两个金属离子，第四个氧原子指向底物结合袋。这种结合模式在这个家族的已知结构中是独特的，但让人想起磷酸盐与脲酶的结合和硫酸盐与A蛋白磷酸酶的结合。结构和动力学支持桥接氧原子引发水解的假设。
Purple acid phosphatases (PAPs) are a family of binuclear metalloenzymes that catalyze the hydrolysis of phosphoric acid esters and anhydrides. A PAP in sweet potato has a unique, strongly antiferromagnetically coupled Fe(III)-Mn(II) center and is distinguished from other PAPs by its increased catalytic efficiency for a range of activated and unactivated phosphate esters, its strict requirement for Mn(II), and the presence of a mu-oxo bridge at pH 4.90. This enzyme displays maximum catalytic efficiency (k(cat)/K-m) at pH 4.5, whereas its catalytic rate constant (k(cat)) is maximal at near-neutral pH, and, in contrast to other PAPs, its catalytic parameters are not dependent on the pK(a) of the leaving group. The crystal structure of the phosphate-bound Fe(III)-Mn(II) PAP has been determined to 2.5-Angstrom resolution (final R-free value of 0.256). Structural comparisons of the active site of sweet potato, red kidney bean, and mammalian PAPs show several amino acid substitutions in the sweet potato enzyme that can account for its increased catalytic efficiency. The phosphate molecule binds in an unusual tripodal mode to the two metal ions, with two of the phosphate oxygen atoms binding to Fe(III) and Mn(II), a third oxygen atom bridging the two metal ions, and the fourth oxygen pointing toward the substrate binding pocket. This binding mode is unique among the known structures in this family but is reminiscent of phosphate binding to urease and of sulfate binding to A protein phosphatase. The structure and kinetics support the hypothesis that the bridging oxygen atom initiates hydrolysis.