The genetics of prions--a contradiction in terms?

Management of a CJD case. Part 1. Preoperative organisation of the case

Recent years have seen the rise of variant Creutzfeldt-Jacob Disease (vCJD), causing great concern amongst the public at large and healthcare professionals, and the implications of the disease are still to be properly determined. In this, the first of two articles, Beverley McNeil outlines the various risk categories of CJD patients, the planning of the case and the handling of associated instrumentation postoperatively. Next month's article will deal with the practicalities surrounding management of the case.

Immunogold Electron Microscopy Recognizes Prion Protein-Associated Particles Prepared from Scrapie-Infected Mouse Brain

Previous studies have proposed that the disease isoform of prion protein (PrPSc) is particulate. Our purpose was to search by electron microscopy (EM) for particles in fractions of density gradients prepared from differentially centrifuged homogenates of scrapie-infected, normal, and null mouse brain. Only mild detergents were used during the separation process. The low-density fractions derived from scrapie-infected brain were rich in PrP. Three morphologically distinct types of particle were observed. Type 1 particles, measuring approximately 6.8 nm in mean diameter, were found in abundance in the fractions of scrapie-infected brain at the peak PrP concentrations. They were often clumped and adherent to raft-like structures. Type 2 particles, in low-density fractions from normal brain, were similar to type 1 but were smaller, with the mean diameter measuring approximately 5.3 nm. Type 3 particles from null brain differed morphologically from types 1 and 2 and were not clumped. The low density of the particles indicated a lipid component, which was confirmed by lipid analysis. Immunogold EM using Mab 6H4 labeled a portion of the particles from scrapie mouse brain, but not those from normal or null brain. Dimensions of PrP suggest that the labeled particles carry a PrPSc dimer per particle.

The risk of transmission of variant Creutzfeldt–Jakob disease via contact lenses and ophthalmic devices

This review collated the available information regarding the risk of transmission of variant Creutzfeldt-Jakob disease (vCJD) via contact lenses and other ophthalmic devices. The topics examined include: the emerging background science of the unconventional infective agent, the prion, particularly those factors affecting transmission; the estimates of the number of undiagnosed infective individuals; and evidence of infectivity in the external eye. Despite many uncertainties in the literature, we conclude that cross-infection is theoretically possible. An assessment of the extensive search for a complete inactivation procedure resulted in the recommendation of the use of sodium hypochlorite (NaOCl), which does not appear to distort rigid lenses. Further tests are required for other devices.

Notes on the history of the prion diseases. Part II

The protein-only theory of transmission of the prion diseases remains controversial. Other mechanisms such as the virus, virino, and viroid hypotheses are still under consideration. All these fit in the concept of 'slow' infections that had been proposed in 1954 by Bjorn Sigurdsson, an Icelandic pathologist. Regardless of the exact mode of infection, the presence of prions in the brain has served to unite Creutzfeldt-Jakob disease (CJD), the Gerstmann-Sträussler-Scheinker syndrome and fatal familial insomnia, as well as scrapie and a number of other animal diseases, into a single pathological entity, the transmissible spongiform encephalopathies. The appearance of bovine spongiform encephalopathy in the United Kingdom and its putative relationship to new variant CJD, have put a new and unpredictable light on these unusual and uncommon diseases.

Prions: disease propagation and disease therapy by conformational transmission

Transmissible spongiform encephalopathies - also known as prion-related diseases - are a group of fatal neurodegenerative disorders associated with the misfolding of prion protein. Several unprecedented scientific findings, which have directly confronted popular dogmas in biology, have put prion research in the spotlight. The experimental evidence supports an entirely novel disease mechanism, involving disease transmission by replication of protein conformation. Here, we describe exciting scientific findings that make the prion field attractively heretical, and we propose the transmission of protein conformation as a novel approach to producing drugs to combat a variety of diseases.

The unfolding pathway and conformational stability of potato carboxypeptidase inhibitor

The unfolding and denaturation curves of potato carboxypeptidase inhibitor (PCI) were investigated using the technique of disulfide scrambling. In the presence of denaturant and thiol initiator, the native PCI denatures by shuffling its native disulfide bonds and converts to form a mixture of scrambled PCI that consists of 9 out of a possible 14 isomers. The denaturation curve is determined by the fraction of native PCI converted to scrambled isomers under increasing concentrations of denaturant. The concentration of guanidine thiocyanate, guanidine hydrochloride, and urea required to denature 50% of the native PCI was found to be 0.7, 1.45, and 8 m, respectively. The PCI unfolding curve was constructed through the analysis of structures of scrambled isomers that were denatured under increasing concentrations of denaturant. These results reveal the existence of structurally defined unfolding intermediates and a progressive expansion of the polypeptide chain. The yield of the beads-form isomer (Cys(8)-Cys(12), Cys(18)-Cys(24), and Cys(27)-Cys(34)) as a fraction of total denatured PCI was shown to be directly proportional to the strength of the denaturing condition. Furthermore, the PCI sequence was unable to fold quantitatively into a single native structure. Under physiological conditions, the scrambled isomers of PCI that constitute about 4% of the protein were in equilibrium with native PCI.

Emerging and re-emerging infectious diseases

Microbial pathogens discovered as aetiological agents of human disease over the last 25 years are reviewed. Strengthening of laboratory and public health surveillance is of paramount importance for early detection and management of emerging infectious diseases.