Alperin E S, Shapiro L J
Department of Pediatrics, University of California San Francisco, San Francisco, California 94143, USA.
J Biol Chem. 1997 Aug 15;272(33):20756-63. doi: 10.1074/jbc.272.33.20756.
X-linked ichthyosis is the result of steroid sulfatase (STS) deficiency. While most affected individuals have extensive deletions of the STS gene, point mutations have been reported in three patients (1). In this study, we identify an additional three point mutations and characterize the effects of all six mutations on STS activity and expression. All six are unique single base pair substitutions. The mutations are located in a 105-amino acid region of the C-terminal half of the polypeptide. Five of the six mutations involve the substitutions of Pro or Arg for Trp372, Arg for His444, Tyr for Cys446, or Leu for Cys341. The other mutation is in a splice junction and results in a frameshift causing premature termination of the polypeptide at residue 427. All the affected residues are conserved to some degree within the sulfatase family. The six mutations were reproduced in normal STS cDNA and transiently expressed in STS-deficient cells. All six mutant vectors direct the expression of STS protein that lacks enzymatic activity. The mutant polypeptides show a shift in mobility on SDS-PAGE and resistance to proteinase K digestion when translated in the presence of dog pancreas microsomes, indicating glycosylation and normal translocation.
X连锁鱼鳞病是类固醇硫酸酯酶（STS）缺乏的结果。虽然大多数受影响个体的STS基因存在广泛缺失，但已有报道三名患者存在点突变（1）。在本研究中，我们鉴定出另外三个点突变，并描述了所有六个突变对STS活性和表达的影响。所有六个都是独特的单碱基对替换。这些突变位于多肽C端一半的一个105个氨基酸的区域。六个突变中的五个涉及用Pro或Arg替换Trp372、用Arg替换His444、用Tyr替换Cys446或用Leu替换Cys341。另一个突变位于剪接连接处，导致移码，使多肽在第427位残基处提前终止。所有受影响的残基在硫酸酯酶家族中都有一定程度的保守性。这六个突变在正常的STS cDNA中重现，并在STS缺陷细胞中瞬时表达。所有六个突变载体都指导缺乏酶活性的STS蛋白的表达。当在狗胰腺微粒体存在的情况下进行翻译时，突变多肽在SDS-PAGE上显示迁移率变化，并对蛋白酶K消化具有抗性，表明存在糖基化和正常转运。
