Characterisation of a gene cluster involved in bacterial degradation of the cyanobacterial toxin microcystin LR
Characterisation of a gene cluster involved in bacterial degradation of the cyanobacterial toxin microcystin LR
复制标题
DOI：
10.1002/tox.10013
复制
发表时间：
2001-12-01
影响因子：
4.5
通讯作者：
Blakeley, RL
中科院分区：
文献类型：
--
作者：
Bourne, DG;Riddles, P;Blakeley, RL
在新分离的鞘氨醇单胞菌属中鉴定了降解蓝藻七肽肝毒素微囊藻毒素LR的新途径（Bourne等人，1996 Appl. Environ. Microbiol. 62：4086-4094）。我们现在报告的克隆和分子特征的四个基因，从这个鞘氨醇单胞菌存在于一个5.8 kb的基因组片段，编码三个水解酶参与这一途径，连同一个假定的寡肽转运蛋白。异源表达的降解途径蛋白具有酶活性。微囊藻毒素酶（Microcystinase，MirA）是降解途径中的第一个酶，是一种336个残基的内肽酶，其与来自热自养甲烷杆菌的假设蛋白质仅显示低的序列同一性。EDTA和1，10-菲咯啉对微囊藻毒素酶的抑制作用表明微囊藻毒素酶是一种金属酶。最有可能螯合活性位点过渡金属离子的残基是序列HXXHXE，这对金属蛋白酶来说是独特的。紧邻转录方向相同的mlrA下游的是基因mlrD，其概念翻译（MlrD，442个残基）显示出与寡肽转运蛋白的PTR 2家族显著的序列同一性和相似的潜在跨膜区。基因mlrB位于mlrA和mlrD基因的下游，但以相反的方向转录。该基因编码酶MlrB（402个残基），该酶将线性微囊藻毒素LR切割成四肽降解产物。这种酶属于活性位点丝氨酸水解酶的“青霉素结合酶”家族。簇mlrC中的最后一个基因位于mlrA基因的上游，并以相反的方向转录。它编码MlrC（507个残基），其介导四肽的进一步溶肽降解。该蛋白质与天蓝色链霉菌的一个假设蛋白质具有显著的序列同一性。基于金属螯合剂的抑制作用，怀疑是一种金属肽酶。与其它微生物比较，推测该基因簇中的基因可能都参与细胞壁肽聚糖循环，并在微囊藻毒素LR的水解中偶然发挥作用。(C)出版社：John Wiley & Sons，Inc.
A novel pathway for degradation of the cyanobacterial heptapeptide hepatotoxin microcystin LR was identified in a newly isolated Sphingomonas sp. (Bourne et al. 1996 Appl. Environ. Microbiol. 62: 4086-4094). We now report the cloning and molecular characterisation of four genes from this Sphingomonas sp. that exist on a 5.8-kb genomic fragment and encode the three hydrolytic enzymes involved in this pathway together with a putative oligopeptide transporter. The heterologously expressed degradation pathway proteins are enzymatically active. Microcystinase (MirA), the first enzyme in the degradative pathway, is a 336-residue endopeptidase, which displays only low sequence identity with a hypothetical protein from Methanobacterium thermoautotrophicum. Inhibition of microcystinase by EDTA and 1,10-phenanthroline suggests that it is a metalloenzyme. The most likely residues that could potentially chelate an active-site transition metal ion are in the sequence HXXHXE, which would be unique for a metalloproteinase. Situated immediately downstream of mlrA with the same direction of transcription is a gene mlrD, whose conceptual translation (MlrD, 442 residues) shows significant sequence identity and similar potential transmembrane spanning regions to the PTR2 family of oligopeptide transporters. A gene mlrB is situated downstream of the mlrA and mlrD genes, but transcribed in the opposite direction. The gene encodes the enzyme MlrB (402 residues) which cleaves linear microcystin LR to a tetrapeptide degradation product. This enzyme belongs to the "penicillin-binding enzyme" family of active site serine hydrolases. The final gene in the cluster mlrC, is located upstream of the mlrA gene and is transcribed in the opposite direction. It codes for MlrC (507 residues) which mediates further peptidolytic degradation of the tetrapeptide. This protein shows significant sequence identity to a hypothetical protein from Streptomyces coelicolor. It is suspected to be a metallopeptidase based on inhibition by metal chelators. It is postulated on the basis of comparison with other microorganisms that the genes in this cluster may all be involved in cell wall peptidoglycan cycling and subsequently act fortuitously in hydrolysis of microcystin LR. (C) 2001 by John Wiley & Sons, Inc.