Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, ON, Canada K9J 7B8.
Biochem Biophys Res Commun. 2010 Aug 27;399(3):347-51. doi: 10.1016/j.bbrc.2010.07.073. Epub 2010 Jul 22.
Giardia lamblia is a pathogenic protist that infects the small intestine of mammals. As a facultative anaerobe, Giardia obtains all of its energy by substrate-level phosphorylation, lacks a functioning respiratory chain, and is not thought to require heme. However, sequencing of the G. lamblia genome has identified several putative heme proteins, one of which shares high sequence similarity to flavohemoglobins found in bacteria and some single-celled eukaryotes. We have cloned and characterized the functional properties of the G. lamblia flavohemoglobin. The protein is monomeric, binds heme and flavin adenine dinucleotide, and exhibits similar behavior to known flavohemoglobins, including NADH and NADPH oxidase activity, which is stimulated by addition of the nitric oxide donor DEA/NO. Based on its structural and functional properties, the likely role of this protein is to protect Giardia against oxygen, nitric oxide, or both. The presence of a Giardia gene encoding a functional heme protein raises questions on how this organism acquires the heme cofactor, which hitherto have been unexplored.
蓝氏贾第鞭毛虫是一种感染哺乳动物小肠的致病原生动物。作为兼性厌氧菌，蓝氏贾第鞭毛虫通过底物水平磷酸化获得所有能量，缺乏功能呼吸链，并且不被认为需要血红素。然而，蓝氏贾第鞭毛虫基因组的测序已经鉴定出几种可能的血红素蛋白，其中一种与细菌和一些单细胞真核生物中发现的黄素血红蛋白具有很高的序列相似性。我们已经克隆并表征了蓝氏贾第鞭毛虫黄素血红蛋白的功能特性。该蛋白是单体的，结合血红素和黄素腺嘌呤二核苷酸，并表现出与已知黄素血红蛋白相似的行为，包括 NADH 和 NADPH 氧化酶活性，一氧化氮供体 DEA/NO 的加入可刺激其活性。基于其结构和功能特性，该蛋白的可能作用是保护贾第虫免受氧气、一氧化氮或两者的侵害。贾第虫基因编码一种具有功能的血红素蛋白的存在提出了关于该生物体如何获得血红素辅因子的问题，迄今为止这些问题尚未得到探索。
