Conformational conversion of the cellular prion protein, PrP^C, into the amyloidogenic isoform, PrP^Sc, is a key pathogenic event in prion diseases. However, the conversion mechanism remains to be elucidated. Here, we generated Tg(PrPΔ91-106)-8545/Prnp^0/0 mice, which overexpress mouse PrP lacking residues 91-106. We showed that none of the mice became sick after intracerebral inoculation with RML, 22L, and FK-1 prion strains nor accumulated PrP^ScΔ91-106 in their brains except for a small amount of PrP^ScΔ91-106 detected in one 22L-inoculated mouse. However, we found they developed disease around 85 days after inoculation with BSE prions with accumulation of PrP^ScΔ91-106 in their brains. These results suggest that residues 91-106 are important for PrP^C conversion into PrP^Sc in infection with RML, 22L, and FK-1 prions but not BSE prions. We then narrowed down the residues 91-106 by transducing various PrP deletional mutants into RML- and 22L-infected cells, and identified that PrP mutants lacking residues 97-99 failed to convert into PrP^Sc in these cells. Our in vitro conversion assay also showed that RML, 22L, and FK-1 prions did not convert PrPΔ97-99 into PrP^ScΔ97-99, but BSE prions did. We further found that PrP mutants with proline residues at positions 97-99 or charged residues at positions 97 and 99 completely or almost completely lost their converting activity into PrP^Sc in RML- and 22L-infected cells. These results suggest that the structurally flexible and non-charged residues 97-99 could be important for PrP^C conversion into PrP^Sc following infection with RML, 22L, and FK-1 prions but not BSE prions.

细胞朊病毒蛋白 PrP ^C向淀粉样蛋白异构体 PrP ^Sc的构象转化是朊病毒疾病的关键致病事件。然而，转换机制仍有待阐明。在这里，我们生成了 Tg(PrPΔ91-106)-8545/ Prnp ^0/0小鼠，它们过表达缺乏残基 91-106 的小鼠 PrP。我们发现，在脑内接种 RML、22L 和 FK-1 朊病毒株后，没有一只老鼠生病，也没有在它们的大脑中积累 PrP ^Sc Δ91-106，除了在一只 22L 接种的小鼠中检测到少量 PrP ^Sc Δ91-106鼠。然而，我们发现他们在接种 BSE 朊病毒后 85 天左右出现疾病，并积累了 PrP ^ScΔ91-106 在他们的大脑中。这些结果表明，在感染 RML、22L 和 FK-1 朊病毒而非 BSE 朊病毒时，残基 91-106 对 PrP ^C转化为 PrP ^{Sc很重要。}然后，我们通过将各种 PrP 缺失突变体转导到 RML 和 22L 感染的细胞中来缩小残基 91-106，并确定缺乏残基 97-99 的 PrP 突变体未能在这些细胞中转化为 PrP ^{Sc 。}我们的体外转化试验还显示 RML、22L 和 FK-1 朊病毒不会将 PrPΔ97-99 转化为 PrP ^ScΔ97-99，但 BSE 朊病毒有。我们进一步发现，在 RML 和 22L 感染的细胞中，在 97-99 位具有脯氨酸残基或在 97 和 99 位具有带电残基的 PrP 突变体完全或几乎完全丧失了其转化为 PrP ^{Sc的活性。}这些结果表明，结构灵活且不带电荷的残基 97-99 可能对感染 RML、22L 和 FK-1 朊病毒而不是 BSE 朊病毒后的 PrP ^C转化为 PrP ^{Sc很重要。}