Insect silk contains both a Kunitz-type and a unique Kazal-type proteinase inhibitor
Insect silk contains both a Kunitz-type and a unique Kazal-type proteinase inhibitor
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DOI：
10.1046/j.1432-1327.2001.02084.x
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发表时间：
2001-04-01
期刊：
影响因子：
--
通讯作者：
Sehnal, F
中科院分区：
文献类型：
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作者：
Nirmala, X;Kodrik, D;Sehnal, F
昆虫丝由结构纤维（丝素）和粘性（丝胶）蛋白组成，并含有一些迄今未知功能的小肽。我们证明，这些肽抑制细菌和真菌的蛋白酶（枯草杆菌蛋白酶，蛋白酶K和链霉蛋白酶）。这些“丝蛋白酶抑制剂”1和2（SPI 1和2）在结茧前在丝分泌腺的中段产生，并且它们的产生在转录水平上受到控制。前SPI 1基因的cDNA全长为443个核苷酸，编码76个氨基酸残基，其中20个氨基酸残基为信号肽。成熟的SPI 1（6056.7 Da，56个残基）是一个典型的热稳定Kunitz型蛋白酶抑制剂，P1位为Arg。前SPI 2的cDNA由260个核苷酸组成，产生一个58个氨基酸残基的推定分泌肽。功能性SPI 2（3993 Da，36个残基）是具有独特结构特征的单结构域Kazal型蛋白酶抑制剂：N-末端的游离片段被还原成单个氨基酸残基，CysI和CysV的缺乏阻止了A-环的形成并为C-环提供了增加的柔性，CysV正常位置周围几个残基的缺失缩短并改变了蛋白质的st螺旋片段。结构揭示了B环的长度和排列，包括pi残基的暴露，以及C末端相对于B环的位置，对于Kazal型抑制剂的活性是必不可少的。
Insect silk is made up of structural fibrous (fibroins) and sticky (sericins) proteins, and contains a few small peptides of hitherto unknown functions. We demonstrate that two of these peptides inhibit bacterial and fungal proteinases (subtilisin, proteinase K and pronase). These 'silk proteinase inhibitors' 1 and 2 (SPI 1 and 2) are produced in the middle Section of the silk-secreting glands prior to cocoon spinning and their production is controlled at transcription level. The full length cDNA of pre-SPI 1 contains 443 nucleotides and encodes a peptide of 76 amino-acid residues, of which 20 make up a signal sequence. The mature SPI 1 (6056.7 Da, 56 residues) is a typical thermostable Kunitz-type proteinase inhibitor with Arg in P1 position. The cDNA of pre-SPI 2 consists of 260 nucleotides and yields a putative secretory peptide of 58 amino-acid residues. The functional SPI 2 (3993 Da, 36 residues) is a single-domain Kazal-type proteinase inhibitor with unique structural features: free segment of the N-terminus is reduced to a single amino-acid residue, lack of CysI and CysV precludes formation of the A-ring and provides increased flexibility to the C-ring, and absence of several residues around the normal position of CysV shortens and changes the st helix segment of the protein. The structure reveals that the length and arrangement of the B-ring, including exposure of the pi residue, and the position of the C-terminus relative to the B-loop, are essential for the activity of the Kazal-type inhibitors.