Bednarek Anika, Wiek Sabine, Lingelbach Klaus, Seeber Frank
FB Biologie/Parasitologie, Philipps-Universität Marburg, Karl-von-Frisch-Str., D-35032, Marburg, Germany.
Exp Parasitol. 2003 Jan-Feb;103(1-2):68-77. doi: 10.1016/s0014-4894(03)00074-2.
Apicomplexan parasites possess an apicoplast-localized redox system consisting of a plant-type ferredoxin-NADP(+)-reductase (FNR) and its redox partner ferredoxin, a small [2Fe-2S] protein. We show here that several apicomplexan FNRs contain unique amino acid insertions of various lengths which are located in close proximity to the enzymatically important FAD and ferredoxin-binding sites of these proteins. Using the insertion of the Toxoplasma gondii reductase as an example we raised epitope-specific antibodies against an 11 amino acids long peptide predicted to be surface-exposed within this insertion. This peptide was found to be immunogenic when presented to the immune system as part of a carrier protein, but also in its natural structural context in the whole recombinant protein, implying that the epitope is surface-exposed. Three-dimensional modeling of T. gondii FNR based on the known 3D-structure of maize root FNR predicts that the overall structure of plant and apicomplexan FNRs are very similar and that the 11 amino acids are part of an alpha-helix, looping out of the molecule. Collectively, these data suggest that the insertion in T. gondii FNR does not affect the overall structure of the protein but may have an effect on the binding dynamics of FAD, NADP(+), and/or ferredoxin to FNR.
顶复门寄生虫拥有一个定位于顶质体的氧化还原系统，该系统由一种植物型铁氧化还原蛋白-NADP(+)-还原酶（FNR）及其氧化还原伙伴铁氧化还原蛋白（一种小的[2Fe-2S]蛋白）组成。我们在此表明，几种顶复门FNR含有各种长度的独特氨基酸插入序列，这些序列位于这些蛋白质酶活性重要的FAD和铁氧化还原蛋白结合位点附近。以刚地弓形虫还原酶的插入序列为例，我们针对预测在该插入序列中暴露于表面的一个11个氨基酸长的肽段产生了表位特异性抗体。当该肽段作为载体蛋白的一部分呈现给免疫系统时，发现其具有免疫原性，而且在整个重组蛋白的天然结构背景中也具有免疫原性，这意味着该表位暴露于表面。基于玉米根FNR已知的三维结构对刚地弓形虫FNR进行的三维建模预测，植物和顶复门FNR的整体结构非常相似，且这11个氨基酸是一个α-螺旋的一部分，从分子中伸出。总体而言，这些数据表明刚地弓形虫FNR中的插入序列不会影响蛋白质的整体结构，但可能会对FAD、NADP(+)和/或铁氧化还原蛋白与FNR的结合动力学产生影响。
