Structural Aspects of Congo Red as an Inhibitor of Protease‐Resistant Prion Protein Formation

• Published in: Journal of neurochemistry Vol. 71; no. 6; pp. 2534 - 2541
• Main Authors: Demaimay, Rémi, Harper, James, Gordon, Heather, Weaver, Donald, Chesebro, Bruce, Caughey, Byron
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Science Ltd 01-12-1998; Blackwell
• Subjects: Animals; Biological and medical sciences; Biphenyl Compounds - metabolism; Cell-Free System - drug effects; Cell‐free system; Coloring Agents - chemistry; Coloring Agents - pharmacology; Congo red; Congo Red - chemistry; Congo Red - metabolism; Congo Red - pharmacology; Cricetinae; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Drug Resistance; Endopeptidases - pharmacology; Energy minimization calculations; Medical sciences; Methylation; Neurology; Prion protein; Prions - antagonists & inhibitors; Prions - metabolism; Protease resistance; Protein Precursors - metabolism; Scrapie; Structural modifications; Transmissible spongiform encephalopathies; Tumor Cells, Cultured; Nervous system diseases; Scrapie; Enzyme; Enzyme inhibitor; Cerebral disorder; Infection; Virus; Peptidases; Congo red; Central nervous system disease; Hydrolases; Degenerative disease; Prion; Spongiform encephalopathy; Slow virus
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1046/j.1471-4159.1998.71062534.x

: Congo red (CR) has been shown to inhibit the accumulation in scrapie‐infected cells of prion protein (PrP) in the abnormal protease‐resistant form (PrP‐res). However, it was not clear if this effect was due to a direct interaction of CR with either PrP‐res or its protease‐sensitive precursor (PrP‐sen) or to a less direct effect on living cells. Here we show that CR inhibits PrP‐res formation in a simple cell‐free reaction composed predominantly of purified PrP‐res and PrP‐sen. Structurally modified CR analogues were also compared in both the cell‐free conversion reaction and scrapie‐infected neuroblastoma cells. Methylation of the central phenyl groups at the 2,2′ positions diminished the inhibitory potency by ≥10‐fold. In contrast, there was little effect of 3,3′ methylation of the phenyls, deletion of one phenyl, or addition of an amido group between the phenyls. The relative activities of these compounds were well correlated in both cellular and acellular systems. Molecular modeling indicated that CR and 3,3′‐methyl‐CR have little rotational restriction about the biphenyl bond and can readily adopt a planar conformation, as can phenyl‐CR and amido‐CR. In contrast, 2,2′‐methyl‐CR is restricted to a nonplanar conformation of the biphenyl group. Thus, planarity and/or torsional mobility of the central phenyl rings of CR and its analogues is probably important for inhibition of PrP‐res formation. On the other hand, variations in the intersulfonate distance in these molecules had little effect on PrP‐res inhibition. These results indicated a high degree of structural specificity in the inhibition of PrP‐res formation by CR and related compounds.