Molecular Basis of Maple Syrup Urine Disease

枫糖尿病（Maple sulphur urine disease，MSUD）是一种因支链α-酮酸脱氢酶复合物（BCKDH）E_1 α、E_1 β或E_2亚基缺乏而引起的常染色体隐性遗传病。我们进行了以下研究，以寻求MSUD的分子基础。我们分离并测序了BCKDH E_2亚基的cDNA插入片段。它由2，649个碱基对组成，开放阅读框为1，431个碱基对，可翻译成477个氨基酸，3 '非翻译区为1，205个碱基对。推测的氨基酸残基为硫辛酰结构域、E_3结合结构域和核心结构域.我们分析了人BCKDH E_1 β亚基的cDNA和基因组cDNA结构。该cDNA克隆含有4个核苷酸的5 '端非翻译序列、1.176个核苷酸的翻译序列和169个核苷酸的3'端非翻译序列。该cDNA编码342个氨基酸的亚基，Mr= 37，585，其包括50个氨基酸的前导序列。E_1 β亚基基因长度超过150 kb，分为10个外显子。所有的剪接供体和受体位点都符合GT/AG规则。转录起始位点位于起始密码子上游47个碱基处。在帽位点上游37个碱基和47个碱基处存在“CAAT”bax及其反向互补序列，但不存在“TATA”box样序列.我们发现了三种不同的突变基因：门诺MSUD的E_1 α亚基基因由T → A替换，日本MSUD家族的E_2亚基基因由78个碱基对的重复序列缺失。

Maple syrup urine disease (MSUD) is an autosomal recessive inherited disorder due to a deficiency of any subunits, E_1 alpha, E_1 beta or E_2 of branched chain alpha-ketoacid dehydrogenase complex (BCKDH). We performed following study to seek a molecular basis of the MSUD.1. We isolated and sequenced a cDNA insert of E_2 subunit of BCKDH. It consists of 2,649 base pairs with and open reading frame of 1,431 base pairs, which can be translated into 477 amino acids, and 3'-untranslated region of 1,205 base pairs. The deduced amino acid residues were a lipoyl-bearing domain, a E_3-binding domain and innor core domain.2. We analyzed cDNA and genomic cDNA structure of E_1beta subunit of human BCKDH. Isolated cDNA clone contained a 5'-untranslated sequence of 4 nucleotides, the translated sequence of 1.176 uncleotides and a 3'-untranslated sequence of 169 nucleotides. The cDNA encodes for a 342 amino acid subunit with a Mr=37,585, which includes a leader sequence of 50 amino acids. The gene of E_1beta subunit is over 150 kb long and splits into 10 exons. All of the splice donor and acceptor sites confirm to the GT/AG rule. The transcription initiation site was located 47 base upstream of the initiation codon. A "CAAT" bax and its reverse complement sequence were present at 37 bases and 47 bases upstream from the cap sites, but there was no "TATA" box like sequence.3. We found 3 different mutant genes ; A T-to-A substitution in the E_1alpha subunit gene in Mennonite MSUD, a deletion of an 11-base pair repeat sequence, which encodes a mitochondrial ratgetting leader peptide, in a Japanese MSUD family and a 78 base pair deletion in E_2 subunit genedue to splicing abnormalities in another Japanese MSUD family.