Structural and Biochemical Characterization of Chlamydia trachomatis Hypothetical Protein CT263 Supports That Menaquinone Synthesis Occurs through the Futalosine Pathway
Structural and Biochemical Characterization of Chlamydia trachomatis Hypothetical Protein CT263 Supports That Menaquinone Synthesis Occurs through the Futalosine Pathway
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DOI：
10.1074/jbc.m114.594325
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发表时间：
2014-11-14
影响因子：
4.8
通讯作者：
Hefty, P. Scott
中科院分区：
文献类型：
--
作者：
Barta, Michael L.;Thomas, Keisha;Hefty, P. Scott
沙眼衣原体是人类特有的细胞内病原体，是致盲沙眼和性传播疾病的病原体。衣原体的基因组测序表明，这种医学上重要的细菌并不完全依赖宿主细胞的能量。为了使电子传输链发挥作用，电子在膜包埋复合体之间的穿梭需要脂溶性的苯二酚(例如，菜籽酮或泛醌)。在沙眼衣原体中获得这些电子载体所需的来源或生物合成途径还知之甚少。沙眼衣原体假定蛋白CT263的1.58埃晶体结构支持其在苯醌生物合成中的作用。尽管CT263缺乏基于序列的功能注释，但CT263的晶体结构与5-甲基硫代腺苷核苷酶(MTAN)具有显著的结构相似性。尽管CT263缺乏在典型MTAN中发现的活性部位相关的二聚体界面，但与产物(腺嘌呤)或底物(5-甲硫基腺苷)的共晶结构表明，典型的活性部位残基是保守的。对CT263的酶学分析表明，呋喃甲苷途径的中间体6-氨基-6-脱氧呋喃甲苷(k(CAT)/K-m=1.8×10(3)m(-1)S(-1))，但不是典型的MTAN底物(如S-腺苷-同型半胱氨酸和5-甲基硫代腺苷)被水解。衣原体蛋白质组的生物信息学分析也支持在衣原体科合成尿喹酮的福他洛辛途径。这份报告首次为衣原体中的苯醌合成提供了实验支持。孟喹酮的合成为抗沙眼衣原体感染的药物提供了另一个靶点。
The obligate intracellular human pathogen Chlamydia trachomatis is the etiological agent of blinding trachoma and sexually transmitted disease. Genomic sequencing of Chlamydia indicated this medically important bacterium was not exclusively dependent on the host cell for energy. In order for the electron transport chain to function, electron shuttling between membrane-embedded complexes requires lipid-soluble quinones (e.g. menaquionone or ubiquinone). The sources or biosynthetic pathways required to obtain these electron carriers within C. trachomatis are poorly understood. The 1.58 angstrom crystal structure of C. trachomatis hypothetical protein CT263 presented here supports a role in quinone biosynthesis. Although CT263 lacks sequence-based functional annotation, the crystal structure of CT263 displays striking structural similarity to 5-methylthioadenosine nucleosidase (MTAN) enzymes. Although CT263 lacks the active site-associated dimer interface found in prototypical MTANs, co-crystal structures with product (adenine) or substrate (5-methylthioadenosine) indicate that the canonical active site residues are conserved. Enzymatic characterization of CT263 indicates that the futalosine pathway intermediate 6-amino-6-deoxyfutalosine (k(cat)/K-m = 1.8 x 10(3) m(-1) s(-1)), but not the prototypical MTAN substrates (e.g. S-adenosylhomocysteine and 5-methylthioadenosine), is hydrolyzed. Bioinformatic analyses of the chlamydial proteome also support the futalosine pathway toward the synthesis of menaquinone in Chlamydiaceae. This report provides the first experimental support for quinone synthesis in Chlamydia. Menaquinone synthesis provides another target for agents to combat C. trachomatis infection.