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Abstract：
A novel apoprotein of an apparent molecular mass of 86 kDa in its unreduced form was identified in human triglyceride-rich lipoproteins. This protein was purified and the amino acid sequence of six proteolytic fragments was found to overlap with that of the factor H-related proteins. In parallel we identified the cDNA encoding a new complement factor H-related protein, termed FHR-4. The sequences of the new apoprotein overlapped with that of the FHR-4 protein. Similar to the previously described factor H-related proteins, FHR-4 contains a hydrophobic signal sequence followed by a stretch of five repetitive elements termed short consensus repeats. Recombinant FHR-4 protein was expressed in the baculovirus system and has an apparent molecular mass of 42 kDa. In addition a 84-kDa dimeric form of the recombinant FHR-4 was detected. Using an immunoaffinity column with antibodies raised against the recombinant FHR-4, we isolated a 86-kDa protein from human plasma. The different molecular mass of the recombinant FHR-4 and the dimeric FHR-4 in plasma is due to different carbohydrate moieties. The 86-kDa plasma protein and the novel apolipoprotein had identical mobility on SDS-polyacrylamide gel electrophoresis analysis and reacted with antisera raised against the reFHR-4 and the purified apoprotein. In conclusion, we have identified a novel factor H-related protein, FHR-4, in human plasma and demonstrate that this protein is present in triglyceride-rich lipoproteins in a dimeric form. This observation provides an intriguing new aspect on possible function(s) of this novel protein and the other factor H-related proteins.
摘要：
在人富含甘油三酸酯的脂蛋白中鉴定出一种未还原形式的表观分子量为86kDa的新型载脂蛋白。纯化该蛋白，发现六个蛋白水解片段的氨基酸序列与因子H相关蛋白的氨基酸序列重叠。同时，我们鉴定了编码一种新的补体因子H相关蛋白的cDNA，称为FHR-4。新载脂蛋白的序列与FHR-4蛋白的序列重叠。类似于先前描述的因子H相关蛋白，FHR-4含有疏水性信号序列,随后是称为短共有重复序列的五个重复元件的延伸。重组FHR-4蛋白在杆状病毒系统中表达并且具有42kDa的表观分子量。此外,检测到84-kDa二聚体形式的重组FHR-4。使用具有针对重组FHR-4的抗体的免疫亲和柱，我们从人血浆中分离了86kDa蛋白。血浆中重组FHR-4和二聚FHR-4的不同分子量是由于不同的碳水化合物部分。86kDa血浆蛋白和新型载脂蛋白在SDS-聚丙烯酰胺凝胶电泳分析中具有相同的迁移率，并与针对reFHR-4和纯化的载脂蛋白产生的抗血清反应。总之,我们已经确定了一种新的因子H相关蛋白，FHR-4在人血浆中，并证明该蛋白质以二聚体形式存在于富含甘油三酸酯的脂蛋白中。该观察结果提供了关于该新型蛋白质和其他因子H相关蛋白质的可能功能的有趣的新方面。
