Wu X W, Lee C C, Muzny D M, Caskey C T
Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030.
Proc Natl Acad Sci U S A. 1989 Dec;86(23):9412-6. doi: 10.1073/pnas.86.23.9412.
Urate oxidase, or uricase (EC 1.7.3.3), is a peroxisomal enzyme that catalyzes the oxidation of uric acid to allantoin in most mammals. In humans and certain other primates, however, the enzyme has been lost by some unknown mechanism. To identify the molecular basis for this loss, urate oxidase cDNA clones were isolated from pig, mouse, and baboon, and their DNA sequences were determined. The mouse urate oxidase open reading frame encodes a 303-amino acid polypeptide, while the pig and baboon urate oxidase cDNAs encode a 304-amino acid polypeptide due to a single codon deletion/insertion event. The authenticity of this single additional codon was confirmed by sequencing the mouse and pig genomic copies of the gene. The urate oxidase sequence contains a domain similar to the type 2 copper binding motif found in other copper binding proteins, suggesting that the copper ion in urate oxidase is coordinated as a type 2 structure. Based upon a comparison of the NH2-terminal peptide and deduced sequences, we propose that the maturation of pig urate oxidase involves the posttranslational cleavage of a six-amino acid peptide. Two nonsense mutations were found in the human urate oxidase gene, which confirms, at the molecular level, that the urate oxidase gene in humans is nonfunctional. The sequence comparisons favor the hypothesis that the loss of urate oxidase in humans is due to a sudden mutational event rather than a progressive mutational process.
尿酸氧化酶，即尿酸酶（EC 1.7.3.3），是一种过氧化物酶体酶，在大多数哺乳动物中催化尿酸氧化为尿囊素。然而，在人类和某些其他灵长类动物中，该酶通过某种未知机制已经丢失。为了确定这种丢失的分子基础，从猪、小鼠和狒狒中分离出尿酸氧化酶cDNA克隆，并测定了它们的DNA序列。小鼠尿酸氧化酶开放阅读框编码一个303个氨基酸的多肽，而猪和狒狒的尿酸氧化酶cDNA由于单个密码子的缺失/插入事件编码一个304个氨基酸的多肽。通过对该基因的小鼠和猪基因组拷贝进行测序，证实了这个额外密码子的真实性。尿酸氧化酶序列包含一个与其他铜结合蛋白中发现的2型铜结合基序相似的结构域，表明尿酸氧化酶中的铜离子以2型结构配位。基于对氨基末端肽和推导序列的比较，我们提出猪尿酸氧化酶的成熟涉及一个六氨基酸肽的翻译后切割。在人类尿酸氧化酶基因中发现了两个无义突变，这在分子水平上证实了人类尿酸氧化酶基因是无功能的。序列比较支持这样一种假说，即人类尿酸氧化酶的丢失是由于突然的突变事件而非渐进的突变过程。
