Papandrikopoulou A, Frey A, Gassen H G
Institut für Biochemie, Technische Hochschule Darmstadt, Federal Republic of Germany.
Eur J Biochem. 1989 Aug 15;183(3):693-8. doi: 10.1111/j.1432-1033.1989.tb21100.x.
In order to understand the mechanisms regulating the blood-brain barrier we isolated a cDNA clone for gamma-glutamyl transpeptidase from purified porcine brain capillaries by cross-species DNA hybridization using a DNA fragment from a rat kidney cDNA clone. The sequence of the porcine gamma-glutamyl transpeptidase cDNA shows 84% identity in the coding region to the sequence of human placenta gamma-glutamyl transpeptidase cDNA. The derived protein sequences of the human and porcine gamma-glutamyl transpeptidase are 98% similar. Alignment of the porcine and the published rat gamma-glutamyl transpeptidase cDNA sequences revealed an average identity of 79%, except for a small region of 194 base pairs containing a high number of mismatches. After four nucleotide changes within this region of the published rat cDNA sequence, which correct two frame shifts, the derived protein sequences of the rat and the porcine gamma-glutamyl transpeptidase show 97% similarity. The corrected sequence, which includes a region of 65 amino acids, contains additional N-glycosylation sites as well as a hydrophobic protein domain that might represent a second membrane-spanning domain. Tissue-specific expression and diversity of the gamma-glutamyl transpeptidase mRNA transcripts in various porcine and human tissues were analysed by Northern blot hybridization. The 2.2-kb transcript of brain gamma-glutamyl transpeptidase is mainly expressed in the endothelial cells of brain microvessels, in agreement with previous data that showed the brain protein being localized within the blood-brain barrier.
为了了解调节血脑屏障的机制，我们使用来自大鼠肾脏cDNA克隆的DNA片段，通过跨物种DNA杂交从纯化的猪脑毛细血管中分离出γ-谷氨酰转肽酶的cDNA克隆。猪γ-谷氨酰转肽酶cDNA的序列在编码区与人胎盘γ-谷氨酰转肽酶cDNA的序列有84%的同一性。人和猪γ-谷氨酰转肽酶的推导蛋白质序列相似性为98%。猪和已发表的大鼠γ-谷氨酰转肽酶cDNA序列的比对显示平均同一性为79%，除了一个194个碱基对的小区域，该区域存在大量错配。在已发表的大鼠cDNA序列的该区域内进行四个核苷酸变化，纠正了两个移码后，大鼠和猪γ-谷氨酰转肽酶的推导蛋白质序列显示出97%的相似性。校正后的序列包括一个65个氨基酸的区域，含有额外的N-糖基化位点以及一个疏水蛋白结构域，该结构域可能代表第二个跨膜结构域。通过Northern印迹杂交分析了γ-谷氨酰转肽酶mRNA转录本在各种猪和人类组织中的组织特异性表达和多样性。脑γ-谷氨酰转肽酶的2.2-kb转录本主要在脑微血管内皮细胞中表达，这与之前显示脑蛋白定位于血脑屏障内的数据一致。
