Cordeiro Y, Machado F, Juliano L, Juliano M A, Brentani R R, Foguel D, Silva J L
Programa de Biologia Estrutural, Departamento de Bioquimica Médica, Instituto de Ciências Biomédicas and Centro Nacional de Ressonância Magnética Nuclear de Macromoléculas, Universidade Federal do Rio de Janeiro, Rio de Janeiro RJ 21941-590, Brazil.
J Biol Chem. 2001 Dec 28;276(52):49400-9. doi: 10.1074/jbc.M106707200. Epub 2001 Oct 16.
The main hypothesis for prion diseases proposes that the cellular protein (PrP(C)) can be altered into a misfolded, beta-sheet-rich isoform (PrP(Sc)), which in most cases undergoes aggregation. In an organism infected with PrP(Sc), PrP(C) is converted into the beta-sheet form, generating more PrP(Sc). We find that sequence-specific DNA binding to recombinant murine prion protein (mPrP-(23-231)) converts it from an alpha-helical conformation (cellular isoform) into a soluble, beta-sheet isoform similar to that found in the fibrillar state. The recombinant murine prion protein and prion domains bind with high affinity to DNA sequences. Several double-stranded DNA sequences in molar excess above 2:1 (pH 4.0) or 0.5:1 (pH 5.0) completely inhibit aggregation of prion peptides, as measured by light scattering, fluorescence, and circular dichroism spectroscopy. However, at a high concentration, fibers (or peptide aggregates) can rescue the peptide bound to the DNA, converting it to the aggregating form. Our results indicate that a macromolecular complex of prion-DNA may act as an intermediate for the formation of the growing fiber. We propose that host nucleic acid may modulate the delicate balance between the cellular and the misfolded conformations by reducing the protein mobility and by making the protein-protein interactions more likely. In our model, the infectious material would act as a seed to rescue the protein bound to nucleic acid. Accordingly, DNA would act on the one hand as a guardian of the Sc conformation, preventing its propagation, but on the other hand may catalyze Sc conversion and aggregation if a threshold level is exceeded.
朊病毒疾病的主要假说认为，细胞蛋白（PrP(C)）可转变为错误折叠的、富含β-折叠的异构体（PrP(Sc)），在大多数情况下，该异构体还会发生聚集。在感染了PrP(Sc)的生物体中，PrP(C)会转变为β-折叠形式，产生更多的PrP(Sc)。我们发现，与重组鼠朊病毒蛋白（mPrP-(23 - 231)）的序列特异性DNA结合会将其从α-螺旋构象（细胞异构体）转变为一种可溶性的、类似于纤维状状态中发现的β-折叠异构体。重组鼠朊病毒蛋白和朊病毒结构域与DNA序列具有高亲和力。当双链DNA序列的摩尔过量超过2:1（pH 4.0）或0.5:1（pH 5.0）时，通过光散射、荧光和圆二色光谱法测量发现，它们能完全抑制朊病毒肽的聚集。然而，在高浓度下，纤维（或肽聚集体）可以解救与DNA结合的肽，使其转变为聚集形式。我们的结果表明，朊病毒 - DNA大分子复合物可能作为生长纤维形成的中间体。我们提出，宿主核酸可能通过降低蛋白质的流动性以及增加蛋白质 - 蛋白质相互作用的可能性来调节细胞构象和错误折叠构象之间的微妙平衡。在我们的模型中，感染性物质将作为种子来解救与核酸结合的蛋白质。因此，DNA一方面作为Sc构象的守护者，阻止其传播，但另一方面，如果超过阈值水平，可能会催化Sc的转化和聚集。
