Dufernez Fabienne, Derelle Evelyne, Noël Christophe, Sanciu Giovanna, Mantini Cléa, Dive Daniel, Soyer-Gobillard Marie-Odile, Capron Monique, Pierce Raymond J, Wintjens René, Guillebault Delphine, Viscogliosi Eric
Institut Pasteur de Lille, Université Lille 2, 59019 Lille cedex, France.
Protist. 2008 Apr;159(2):223-38. doi: 10.1016/j.protis.2007.11.005. Epub 2008 Feb 13.
Superoxide dismutases (SODs) are a family of antioxidant enzymes that catalyse the degradation of toxic superoxide radicals in obligate and facultative aerobic organisms. Here, we report the presence of a multi-copy gene family encoding SODs in the heterotrophic dinoflagellate Crypthecodinium cohnii. All the genes identified (sod1 to sod17) have been cloned and sequenced, and shown to encode potentially functional dimeric iron-containing SOD isozymes. Our data revealed a considerable molecular heterogeneity of this enzyme in C. cohnii at both genomic and transcriptional levels. The C. cohnii SOD1, overexpressed in Escherichia coli, was active and its structure obtained by homology modeling using X-ray crystal structures of homologues exhibited the typical fold of dimeric FeSODs. Phylogenetic studies including 110 other dimeric FeSODs and closely related cambialistic dimeric SOD sequences showed that the C. cohnii SODs form a monophyletic group and have all been acquired by the same event of horizontal gene transfer. It also revealed a dichotomy within the C. cohnii SOD sequences that could be explained by an ancestral sod gene duplication followed by subsequent gene duplications within each of the two groups. Enzyme assays of SOD activity indicated the presence of two FeSOD activities in C. cohnii cell lysate whereas MnSOD and Cu/ZnSOD were not detected. These activities contrasted with the SOD repertoire previously characterized in photosynthetic dinoflagellates. To explain these differences, a hypothetical evolutionary scenario is proposed that suggests gains and losses of sod genes in dinoflagellates.
超氧化物歧化酶（SODs）是一类抗氧化酶，可催化专性和兼性需氧生物中毒性超氧自由基的降解。在此，我们报告在异养甲藻隐甲藻（Crypthecodinium cohnii）中存在一个编码SODs的多拷贝基因家族。所有鉴定出的基因（sod1至sod17）均已克隆并测序，且显示编码潜在功能性的二聚体含铁SOD同工酶。我们的数据揭示了该酶在隐甲藻中基因组和转录水平上存在相当大的分子异质性。在大肠杆菌中过表达的隐甲藻SOD1具有活性，其通过使用同源物的X射线晶体结构进行同源建模获得的结构展现出二聚体FeSOD的典型折叠。系统发育研究包括其他110种二聚体FeSOD和密切相关的兼性二聚体SOD序列，结果表明隐甲藻SODs形成一个单系群，并且全部通过同一水平基因转移事件获得。研究还揭示了隐甲藻SOD序列内的二分法，这可以通过一个祖先sod基因复制，随后在两组中的每组内进行后续基因复制来解释。SOD活性的酶活性测定表明在隐甲藻细胞裂解物中存在两种FeSOD活性，而未检测到MnSOD和Cu/ZnSOD。这些活性与先前在光合甲藻中表征的SOD种类形成对比。为了解释这些差异，提出了一种假设的进化情景，表明甲藻中sod基因的获得和丢失情况。
