Riboflavin transporter deficiency 2 (RTD2) is a rare neurological disorder caused by mutations in the Solute carrier family 52 member 2 (Slc52a2) gene encoding human riboflavin transporter 2 (RFVT2). This transporter is ubiquitously expressed and mediates tissue distribution of riboflavin, a water-soluble vitamin that, after conversion into FMN and FAD, plays pivotal roles in carbohydrate, protein, and lipid metabolism. The 3D structure of RFVT2 has been constructed by homology modeling using three different templates that are equilibrative nucleoside transporter 1 (ENT1), Fucose: proton symporter, and glucose transporter type 5 (GLUT5). The structure has been validated by several approaches. All known point mutations of RFVT2, associated with RTD2, have been localized in the protein 3D model. Six of these mutations have been introduced in the recombinant protein for functional characterization. The mutants W31S, S52F, S128L, L312P, C325G, and M423V have been expressed in E. coli, purified, and reconstituted into proteoliposomes for transport assay. All the mutants showed impairment of function. The K_m for riboflavin of the mutants increased from about 3 to 9 times with respect to that of WT, whereas V_max was only marginally affected. This agrees with the improved outcome of most RTD2 patients after administration of high doses of riboflavin.

中文翻译：

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自然突变对核黄素转运蛋白 2 的影响及其与人类核黄素转运蛋白缺乏症 2 的相关性

核黄素转运蛋白缺乏症 2 (RTD2) 是一种罕见的神经系统疾病，由编码人核黄素转运蛋白 2 (RFVT2) 的溶质载体家族 52 成员 2 (Slc52a2) 基因突变引起。这种转运蛋白广泛表达并介导核黄素的组织分布，核黄素是一种水溶性维生素，在转化为 FMN 和 FAD 后，在碳水化合物、蛋白质和脂质代谢中起关键作用。RFVT2 的 3D 结构是通过同源性建模使用三种不同的模板构建的，这些模板是平衡核苷转运蛋白 1 (ENT1)、岩藻糖：质子转运蛋白和葡萄糖转运蛋白 5 型 (GLUT5)。该结构已通过多种方法得到验证。所有已知的与 RTD2 相关的 RFVT2 点突变都已在蛋白质 3D 模型中定位。这些突变中的六个已被引入重组蛋白以进行功能表征。突变体 W31S、S52F、S128L、L312P、C325G 和 M423V 已在大肠杆菌，纯化，并重组为蛋白脂质体，用于运输测定。所有突变体均表现出功能受损。突变体核黄素的K _m相对于 WT 从大约 3 倍增加到 9 倍，而V _max仅受到轻微影响。这与大多数 RTD2 患者在给予高剂量核黄素后改善的结果一致。