Winter H, Hofmann I, Langbein L, Rogers M A, Schweizer J
German Cancer Research Center, Im Neuenheimer Feld 280, 69120 Heidelberg, Germany.
J Biol Chem. 1997 Dec 19;272(51):32345-52. doi: 10.1074/jbc.272.51.32345.
In this study, we have elucidated the molecular mechanisms underlying the expression of an acidic 41-kDa protein inherited as an autosomal dominant trait of the hair keratin pattern of about 5% of the human population. We show that this protein is a size variant of the large type I hair cortex keratin hHa1 due to a genetic polymorphism in the hHa1 gene. We detected a G-A substitution in the 5' splice site of intron 6 of the hHa1 gene, which segregates with the 41-kDa protein phenotype in two pedigrees and is responsible for the formation of an abnormally spliced hHa1 mRNA species. The use of an alternative 5' splice site leads to the retention of 41 nucleotides of the initial intron 6 sequences in the mature transcript. The open reading frame of the aberrant mRNA creates a premature stop codon immediately downstream of the mutation site. The resulting hHa1 protein variant, hHa1-t, is about 6-kDa smaller than the 47-kDa hHa1 hair keratin and lacks the complete nonhelical tail domain. We show that the tailless hHa1-t is functional, since both recombinant hHa1 and hHa1-t form identical keratin intermediate filaments when assembled in vitro with a type II hair keratin partner. This finding confirms the view of a noninvolvement of the keratin tail domain in filament assembly and explains the lack of a pathological hair phenotype in hHa1-t positive individuals.
在本研究中，我们阐明了一种酸性41 kDa蛋白表达的分子机制，该蛋白作为常染色体显性性状遗传，约5%的人类群体具有这种毛发角蛋白模式。我们发现，由于hHa1基因的遗传多态性，这种蛋白是大型I型毛发皮质角蛋白hHa1的一种大小变体。我们在hHa1基因第6内含子的5'剪接位点检测到一个G-A替换，在两个家系中，该替换与41 kDa蛋白表型共分离，并且是异常剪接的hHa1 mRNA形成的原因。使用替代的5'剪接位点导致成熟转录本中保留了初始第6内含子序列的41个核苷酸。异常mRNA的开放阅读框在突变位点下游立即产生一个提前终止密码子。产生的hHa1蛋白变体hHa1-t比47 kDa的hHa1毛发角蛋白小约6 kDa，并且缺少完整的非螺旋尾结构域。我们发现无尾的hHa1-t具有功能，因为当在体外与II型毛发角蛋白伴侣组装时，重组hHa1和hHa1-t形成相同的角蛋白中间丝。这一发现证实了角蛋白尾结构域不参与丝组装的观点，并解释了hHa1-t阳性个体中缺乏病理性毛发表型的原因。
