Grab D J, Lonsdale-Eccles J D, Oli M W, Corbeil L B
Department of Parasitology, Kurume University School of Medicine, Fukuoka, Japan.
J Parasitol. 2001 Oct;87(5):1064-70. doi: 10.1645/0022-3395(2001)087[1064:LBPOTF]2.0.CO;2.
Tritrichomonas foetus is a common, sexually transmitted, protozoan parasite of cattle. It has an essential requirement for iron, which it obtains from host lactoferrin. However, specific lactoferrin-binding protein receptors have not yet been identified in T. foetus. To differentiate specific and nonspecific binding of lactoferrin, lactoferrin affinity chromatography and Western blotting was used to identify metabolically or surface-labeled T. foetus lactoferrin-binding proteins. Bovine lactoferrin was shown to bind more efficiently than human lactoferrin, and each of these bound much better than bovine transferrin. This is relevant because T. foetus is both species-specific and only infects the mucosal surface of the reproductive tract, which has little transferrin. Whereas the majority of lactoferrin binding was specific, competitive inhibition studies showed that nonspecific, charge-related binding of lactoferrin to T. foetus may also be involved. In the presence of bovine cervical mucus, binding of lactoferrin to T. foetus was diminished, suggesting that mucus has an effect on lactoferrin binding. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of surface biotinylated proteins affinity-purified on lactoferrin-Sepharose showed biotinylated bands at Mr values of 22, 49, 55, 72, and 155 kDa. Because lactoferrin-binding proteins may be susceptible to digestion by T. foetus extracellular cysteine proteinases, it is suspected that the 155-kDa protein is the specific lactoferrin-binding protein and that the lower-Mr lactoferrin-binding molecules may be fragmentation products that contain the lactoferrin-binding site; however, other interpretations are clearly feasible. It is possible that there may be multiple proteins or multimers of the same protein. In summary, the data showed that binding of lactoferrin to T. foetus may be regulated by an interplay of specific receptor interactions as well as by hydrophobic and charge-related interactions.
胎儿三毛滴虫是牛常见的性传播原生动物寄生虫。它对铁有绝对需求，通过从宿主乳铁蛋白中获取铁来满足这一需求。然而，尚未在胎儿三毛滴虫中鉴定出特异性乳铁蛋白结合蛋白受体。为了区分乳铁蛋白的特异性和非特异性结合，采用乳铁蛋白亲和层析和蛋白质印迹法来鉴定经代谢标记或表面标记的胎儿三毛滴虫乳铁蛋白结合蛋白。结果表明，牛乳铁蛋白比人乳铁蛋白结合更有效，且二者的结合都比牛转铁蛋白好得多。这很重要，因为胎儿三毛滴虫具有物种特异性，且仅感染生殖道的黏膜表面，而该部位转铁蛋白含量很少。虽然大多数乳铁蛋白结合是特异性的，但竞争抑制研究表明，乳铁蛋白与胎儿三毛滴虫的非特异性、电荷相关结合也可能参与其中。在存在牛宫颈黏液的情况下，乳铁蛋白与胎儿三毛滴虫的结合减少，这表明黏液对乳铁蛋白结合有影响。对在乳铁蛋白 - 琼脂糖凝胶上亲和纯化的表面生物素化蛋白进行十二烷基硫酸钠 - 聚丙烯酰胺凝胶电泳，结果显示在分子量为22、49、55、72和155 kDa处有生物素化条带。由于乳铁蛋白结合蛋白可能易受胎儿三毛滴虫细胞外半胱氨酸蛋白酶的消化作用影响，因此怀疑155 kDa的蛋白是特异性乳铁蛋白结合蛋白，而分子量较低的乳铁蛋白结合分子可能是含有乳铁蛋白结合位点的片段化产物；然而，其他解释显然也是可行的。可能存在多种蛋白质或同一蛋白质的多聚体。总之，数据表明乳铁蛋白与胎儿三毛滴虫的结合可能受特异性受体相互作用以及疏水和电荷相关相互作用的共同调节。
