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Size Matters?!

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Kathy

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For those of you interested in some reading, check out a new "letter" [report] from the Rocky Mountain Lab researchers called:

"The most infectious prion protein particles"

Jay R. Silveira, Gregory J. Raymond, Andrew G. Hughson, Richard E. Race, Valerie L. Sim, Stanley F. Hayes, and Byron Caughey


Abstract
Neurodegenerative diseases such as Alzheimer's, Parkinson's and the transmissible spongiform encephalopathies (TSEs) are characterized by abnormal protein deposits, often with large amyloid fibrils. However, questions have arisen as to whether such fibrils or smaller subfibrillar oligomers are the prime causes of disease1, 2. Abnormal deposits in TSEs are rich in PrPres, a protease-resistant form of the PrP protein with the ability to convert the normal, protease-sensitive form of the protein (PrPsen) into PrPres (ref. 3). TSEs can be transmitted between organisms by an enigmatic agent (prion) that contains PrPres (refs 4 and 5). To evaluate systematically the relationship between infectivity, converting activity and the size of various PrPres-containing aggregates, PrPres was partially disaggregated, fractionated by size and analysed by light scattering and non-denaturing gel electrophoresis. Our analyses revealed that with respect to PrP content, infectivity and converting activity peaked markedly in 17−27-nm (300−600 kDa) particles, whereas these activities were substantially lower in large fibrils and virtually absent in oligomers of 5 PrP molecules. These results suggest that non-fibrillar particles, with masses equivalent to 14−28 PrP molecules, are the most efficient initiators of TSE disease.

This throws a big wrench in the "infectious" theory. How come only prion aggregates of a "specific size variant" are capable of initiating further PrPC mutation?

Another quote from the summary discussion which is suggesting that other factors make up the content of the aggregates, which have not been identified yet (at least not by mainstream infectioun promotors):

PrP content of PrP-res aggregates

Based on protein assays and ultra-microbalance measurements, 47±9% of the vacuum-dried weight of the washed, unfractionated SUS-treated PrP-res particles was protein (data not shown), and, according to semi-quantitative western blots (data not shown), >87% of the protein was PrP. Adjusting for the glycan and glycophosphatidylinositol content (~25%) of PK-treated PrP molecules, we estimate that at least 54% of the mass was attributable to PrP molecules
 

HAY MAKER

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Sandhusker said:
It's not the size of your prion, it's how you mutate it. :lol:

:D :D :D ....................that's what my canadian hussie sez..........good luck
 

Mike

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Chapter 3. Problems associated with measurement of coupling constants in proteins
Traditional one-dimensional 1H NMR spectroscopy is sufficient to provide information on chemical shifts and coupling constants in small organic molecules. Owing to the long transverse relaxation times, proton resonances have very narrow line widths in comparison with the inhomogeneity of the magnetic field. Hence, relatively small coupling constants can often be measured with high accuracy from a well-dispersed spectrum.

In the case of biological macromolecules, the situation is very different for two reasons: increased spectral overlap and faster transverse relaxation of protons. The number of proton resonances in the same rather limited chemical shift range increases rapidly as the protein size increases. For example, a 10-kDa protein has approximately 100 amide proton resonances in the chemical shift range of 3 to 4 ppm. In the case of a 30-kDa protein, the number of resonances is on the order of 300. In addition, as the isotropic molecular rotational correlation time, τc, increases with increasing molecular weight, the line width is dictated by the shorter transverse relaxation time of the corresponding spin instead of magnetic field inhomogeneity. Ultimately, the line width is larger than the coupling constant of interest. These two dilemmas make it impossible to obtain structurally important vicinal proton-proton coupling constants simply from a 1D proton spectrum.

An obvious solution to the overlap problem is to increase the dimensionality of the spectrum. For example, a two-dimensional phase-sensitive COSY experiment (Marion et al. 1983) has been successfully used with small proteins. The dispersion of the proton signals in the COSY spectrum is to the power of two better than in the 1D proton spectrum. However, applicability of the phase-sensitive COSY is limited to small proteins, because in the case of determination of 3JHNHα, the cross-peak intensity between 1HN and 1Hα is low due to self-cancellation of antiphase splitting in the presence of broad lines. Furthermore, the magnitude of the coupling constant is not accurate because the antiphase splitting greatly overestimates the true coupling constant (Neuhaus et al. 1985). For this reason, several line-fitting techniques have been developed for the extraction of the true coupling constant in the phase-sensitive COSY experiment (Neuhaus et al. 1985).

One major limitation of homonuclear experiments stems from the rapid transverse relaxation of protons. This reduces their usability for protein structure determination due to coherence transfer inefficiency in multi-dimensional experiments. Proton relaxation is dominated by the large dipole-dipole (DD) interaction between protons in the protein main-chain and side-chains. Consequently, the proton line width increases rapidly with increasing rotational correlation time. As can be seen from Figure 1a, the proton line width is close to 10 Hz when the correlation time is of the order 10 ns. In contrast, the line width of the backbone amide nitrogen is less than 5 Hz (Figure 1b). It is then obvious that the development of heteronuclear correlation experiments, which allow a greater dispersion of NMR signals with higher coherence transfer efficiency, is indispensable for larger proteins.
 

CattleCo

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"It's not the size of your prion, it's how you mutate it. "

I :lol: don't care who you are....THAT'S FUNNY!!
 

Kathy

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Is anybody else having problems logging onto some of the threads? My computer is freezing up on some, but not others.

As for this study out from Rocky Mountain Labs, I guess there is alot of work that needs to be done on what is found within these aggregates of PrP proteins which exerts the energy required to misfold and recruite other proteins, etc.

Reading up on single-molecule-magnets, it is plausible that the right metals have come together in just the right ratio to cause/induce an electromagnetic field. An electromagnetic particle could be the core of the aggregate?

Once again, can anyone explain how prions are "infectious", when only aggregates of a specific "not too big, not too small" size are involved.
 

the chief

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Kathy asked:

Is anybody else having problems logging onto some of the threads? My computer is freezing up on some, but not others.


Actually, Kathy, my computer isn't freezing up on some posts. It is actually melting whenever I click on something from somebody in SD. I think it is all the Hot air. :wink:
 

mrj

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the chief said:
Kathy asked:

Is anybody else having problems logging onto some of the threads? My computer is freezing up on some, but not others.


{Actually, Kathy, my computer isn't freezing up on some posts. It is actually melting whenever I click on something from somebody in SD. I think it is all the Hot air. :wink:

You poor thing! Who is forcing you to read them?????

MRJ}
 

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