Bundgaard J R, Vuust J, Rehfeld J F
Department of Clinical Biochemistry, State University Hospital, Copenhagen, Denmark.
EMBO J. 1995 Jul 3;14(13):3073-9. doi: 10.1002/j.1460-2075.1995.tb07310.x.
Tyrosine O-sulfation is a common post-translational modification of secretory and membrane proteins. The biological function of sulfation is known in only a few proteins, where it appears to enhance protein-protein interactions. Based on known sequences around sulfated tyrosines, a consensus sequence for prediction of target tyrosines has been proposed. However, some proteins are tyrosine sulfated at sites that deviate from the proposed consensus. Among these is progastrin. It is possible that the deviation explains the incomplete sulfation characteristic for bioactive gastrin peptides. In order to test this hypothesis, we have performed site-directed mutagenesis of the gastrin gene followed by heterologous expression in an endocrine cell line. The results show that substitution of the alanyl residue immediately N-terminal to the sulfated tyrosine with an acidic amino acid promotes the sulfation of gastrin peptides. Hence, the study supports the proposed consensus sequence for tyrosine sulfation. Importantly, however, the results also reveal that complete sulfation increases the endoproteolytic maturation of progastrin. Thus, our study suggests an additional function for tyrosine sulfation of possible general significance.
酪氨酸O-硫酸化是分泌蛋白和膜蛋白常见的翻译后修饰。硫酸化的生物学功能仅在少数蛋白质中已知，在这些蛋白质中它似乎增强了蛋白质-蛋白质相互作用。基于硫酸化酪氨酸周围的已知序列，已经提出了预测靶酪氨酸的共有序列。然而，一些蛋白质在偏离所提出的共有的位点发生酪氨酸硫酸化。胃泌素原就是其中之一。这种偏差可能解释了生物活性胃泌素肽不完全硫酸化的特征。为了验证这一假设，我们对胃泌素基因进行了定点诱变，然后在内分泌细胞系中进行异源表达。结果表明，将硫酸化酪氨酸紧邻的N端丙氨酸残基替换为酸性氨基酸可促进胃泌素肽的硫酸化。因此，该研究支持了所提出的酪氨酸硫酸化共有序列。然而，重要的是，结果还表明完全硫酸化会增加胃泌素原的内蛋白水解成熟。因此，我们的研究表明酪氨酸硫酸化可能具有普遍意义的额外功能。
