Properties of normal and mutant recombinant human ketohexokinases and implications for the pathogenesis of essential fructosuria
Properties of normal and mutant recombinant human ketohexokinases and implications for the pathogenesis of essential fructosuria
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DOI：
10.2337/diabetes.52.9.2426
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发表时间：
2003-09-01
期刊：
影响因子：
7.7
通讯作者：
Bonthron, DT
中科院分区：
文献类型：
--
作者：
Asipu, A;Hayward, BE;Bonthron, DT
酮己糖激酶（果糖激酶）基因的选择性剪接产生一种“中央”主要肝亚型（酮己糖激酶-C）和一种分布更广泛的酮己糖激酶-A。已知只有丰富的肝同种型具有活性，外周组织中较低水平的酮己糖激酶-A没有功能。肝脏酮己糖激酶缺乏导致良性疾病原发性果糖尿。其分子基础已在一个家族中确定（突变Gly 40 Arg和Ala 43 Thr的复合杂合性）。在这里，我们表明，这两个酮己糖激酶亚型确实是活跃的。己酮激酶-A对果糖的底物亲和力比己酮激酶-C差得多，但热稳定性高得多。Gly 40 Arg突变似乎是无效的，使得己酮激酶-A和己酮激酶-C都失活并且很大程度上不溶。Ala 43 Thr突变体保留活性，但该突变降低了己酮激酶-A和己酮激酶-C的热稳定性。在生理温度下，这导致己酮激酶-C活性的显著丧失，但不导致己酮激酶-A活性的显著丧失。因此，携带两种突变的受影响个体可能具有选择性肝己酮糖激酶缺乏，外周己酮糖激酶-A被保留。这些发现提出了一种可能性，即酮己糖激酶-A提供了一个未知的生理功能，在原发性果糖尿保持完整。在这种罕见的疾病的进一步突变分析可以阐明的问题，是否已酮激酶A的活性，不像已酮激酶C，生理上是不可或缺的。
Alternative splicing of the ketohexokinase (fructokinase) gene generates a "central" predominantly hepatic isoform (ketohexokinase-C) and a more widely distributed ketohexokinase-A. Only the abundant hepatic isoform is known to possess activity, and no function is defined for the lower levels of ketohexokinase-A in peripheral tissues. Hepatic ketohexokinase deficiency causes the benign disorder essential fructosuria. The molecular basis of this has been defined in one family (compound heterozygosity for mutations Gly40Arg and Ala43Thr). Here we show that both ketohexokinase isoforms are indeed active. Ketohexokinase-A has much poorer substrate affinity than ketohexokinase-C for fructose but is considerably more thermostable. The Gly40Arg mutation seems null, rendering both ketohexokinase-A and ketohexokinase-C inactive and largely insoluble. The Ala43Thr mutant retains activity, but this mutation decreases the thermal stability of both ketohexokinase-A and ketohexokinase-C. At physiologic temperature, this results in significant loss of ketohexokinase-C activity but not of ketohexokinase-A. Affected individuals who carry both mutations therefore probably have a selective deficiency of hepatic ketohexokinase, with peripheral ketohexokinase-A being preserved. These findings raise the possibility that ketohexokinase-A serves an unknown physiologic function that remains intact in essential fructosuria. Further mutation analysis in this rare disorder could illuminate the question of whether ketohexokinase-A activity is, unlike that of ketohexokinase-C, physiologically indispensable.