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Doubts raised on laminin receptor role
Prion rods contain small amounts of two host sphingolipids
Dealler suggests pentosan might halt the spread of CJD
Deaths from dementia may hide cases of new variant CJD
Genomic structure of complete bovine PrP gene
Design of peptides undergoing alpha-to-beta transition and amyloidogenesis
Molecular evolution in relation to spongiform disease
Dapsone to delay symptoms in Creutzfeldt-Jakob disease
What the dentist needs to know about TSEs

Doubts raised on laminin receptor role

11 August 1997 webmaster opinion
Nothing further on prion protein binding to 37k laminin receptor has been heard from Weiss' group since the Riger R et al Nat.Med 3 1383 (1997) article. However, just out in J Mol Evol 15(8)1017-25 (1998) from Ardini E et al is an excellent history of this remarkable protein [SP accession Q16471 in humans].

One very basic mystery remains unresolved: the covalent modifications that bring 37LRP to its mature form, 67LR; acylation with palmitate, oleate, and stearate is on the table.

37 LRP belongs to a family of ribosomal proteins nearly invariant over time: only 1.7% divergence between chicken and mouse. Homology can be traced back to procaryotic ribosomal S2 proteins. In yeast, which do not produce laminin, it is closest (60% identity) to YST1. Be this as it may, the auxillary function of stabilizing binding of laminin : integrin-like receptor was observed again here in a 20-residue 37 LRP peptide from 161-180 containing palindromic LMWWML. This same domain was cited by Weiss as the part of LRP that bound to prion protein

This property had emerged by the time of divergence of drosophila and nematode LRPs, M90422 and Z37983, correlated with a marked slowdown in evolutionary change. The authors say that it is not that unusual for ribosomal proteins to have auxillary functions.

More troublesome for our purposes is Ardini's observation (noted earlier in Chen MS et al BBA 1297: 124 1996) that the N-terminal part of 37 LRP has 'significant similarities' to various members of the Hsp70 chaperonin family. (Hsp P30721 etc. showed up for me weakly in a quick Blastp against Q16471.) Recall an earlier paper from the Weiss' group, Edenhofer et al J Virol 70: 4714 (1996), in which Hsp60 and GroEl chaperonins interacted with residues 180-210 of prion protein. The yeast two-hybrid screen would produce 37LRP, not the mature form.

Also, Swiss Protein is now saying for human LRP entry Q16471, "-!- caution: Similarity: belongs to the s2p family of ribosomal proteins was originally thought to be a laminin receptor," making me wonder if laminin binding itselfby 37LRP is itself an artefact attributable to the chaperonin moiety.

Thus if 37 LRP is ultimately just a ribosomal protein chaperonin, this vitiates any significance of prion binding because chaperonins bind all manner of probes. As things stand, there seems to be diminished support for meaningful in vivo binding of native prion protein with mature 67LR laminin receptor.

Q16471 human 37LRP


Prion rods contain small amounts of two host sphingolipids as revealed by TLC - MS

Biol Chem 1998 Jun;379(6):655-666 
Klein TR, Kirsch D, Kaufmann R, Riesner D
Sphingolipids were detected in prions, the agents of transmissible spongiform encephalopathies. The analysis was carried out on highly purified, infectious prion rods, which are composed mainly of insoluble aggregates of the N-terminally truncated prion protein, so-called PrP 27-30. Lipid classes were quantified by high performance thin-layer chromatography with a detection limit of 25-50 ng per lipid class. Matrix-assisted laser desorption/ionization mass spectrometry was applied for the first time to lipid analysis in complex biological samples.

A newly developed preparation technique improved the sensitivity to 1-20 pg per molecular species. Only the sphingolipids, galactosylceramide and sphingomyelin, were consistently observed in chloroform/methanol (2:1 v/v) extracts of prion rods. The molar ratio of PrP to the sphingolipids was between 2:1 and 40:1, depending on the purity of the prion preparation. The same lipids were also present in the low density fraction of a gradient centrifugation of prion-rods after sonication in 0.2% SDS.

From the two alternatives, that the sphingolipids are either required for prion function or are relics from the cellular location of PrP in caveolae, the second alternative appears more plausible since the preparation of highest specific infectivity contained the lowest amount of sphingolipids.

Dealler suggests pentosan might halt the spread of CJD

July 29/98 ABC News Jenifer Joseph
The article looked at Dr. Stephen Dealler and his latest findings regarding Creutzfeldt-Jakob disease (CJD) and Bovine Spongiform Encephalopathy (BSE). The article stated that on Thursday, he'll present data about a drug, Pentosan, that might slow the progress of CJD transmission in humans.

Correspondent: "I called a United States Drug Store information number about Pentosan and the pharmacist told me the following: it comes in both oral and injectable form. She said the side effects for the oral are diarrhea, nauseau, water retention, headache, dizziness, elevated liver enzymes. In addition, for the injectable there is bruising at the injection site.

The oral is made out of 100 mg. pentosan (synthetic polyachrate), and the inactive ingredients are magnesium sterate and microcrystalline cellulose. She did not know the ingredients in the injectable except, I think she said for the pentosan. She did not know what the dillutant was made out of ."

Sulfated glycans stimulate endocytosis of the cellular isoform of the prion protein

 J Biol Chem 270: 30221-30229 (1995)
 S. L. Shyng, S. Lehmann, K. L. Moulder &  D. A. Harris
There is currently no effective therapy for human prion diseases. However, several polyanionic glycans, including pentosan sulfate and dextran sulfate, prolong the incubation time of scrapie in rodents, and inhibit the production of the scrapie isoform of the prion protein (PrPSc), the major component of infectious prions, in cultured neuroblastoma cells.

We report here that pentosan sulfate and related compounds rapidly and dramatically reduce the amount of PrPC, the non-infectious precursor of PrPSc, present on the cell surface. This effect results primarily from the ability of these agents to stimulate endocytosis of PrPC, thereby causing a redistribution of the protein from the plasma membrane to the cell interior.

Pentosan sulfate also causes a change in the ultrastructural localization of PrPC, such that a portion of the protein molecules are shifted into late endosomes and/or lysosomes. In addition, we demonstrate, using PrP-containing bacterial fusion proteins, that cultured cells express saturable and specific surface binding sites for PrP, many of which are glycosaminoglycan molecules. Our results raise the possibility that sulfated glycans inhibit prion production by altering the cellular localization of PrPC precursor, and they indicate that endogenous proteoglycans are likely to play an important role in the cellular metabolism of both PrPC and PrPSc. I suspect that they may mean pentosan polysulfate (xylan polysulfate) which is a charged polysaccharide (heparin-like)used as an anticoagulant and an antiviral agent, specifically aainst retroviruses. It has been used for HIV and tumour treatment. The NIH recently gave Caughey the research dollars to add three more scientists to his staff, so they can speed up their study of an entirely new class of such inhibitors. Nonetheless, Caughey said, researchers don't want to give patients a false >sense of hope. "The reality is we don't have anything that is ready to go >not even close, and that's a terrible thing." That's great that they got 3 new staff positions. I have not heard any specifics on this new chemical class of inhibitor. Obviously the lab is well positioned to screen compounds in vitro using their conversion assay. I was told some months back that the idea came from Caughey's father, a biochemist.

Beta-sheet breaker peptides inhibit fibrillogenesis in a rat brain model of amyloidosis: implications for Alzheimer's therapy.

Nat Med. 1998 Jul; 4(7): 822-826
C Soto alludes to an implausible pentapeptide disruptor of prion aggregate in this paper. The idea is a competitive inhibitor for intra-fibril binding sites, not capping. Partial disaggregation could be extremely dangerous and accelerate the course of the disease. Here again there is the problem of the compound reaching its target in vivo.

Deaths from dementia may hide cases of new variant CJD

BMJ 1998 Aug 1;317(7154):E free full text
Azeem Majeed et al.
"Using the 5 year age bands, we then calculated mortality directly standardised for age for each year, using the population of England and Wales in 1979 as the standard population. Because changes in the coding of death certificates in 1984 and 1993 led to artefactual changes in mortality for neurological disorders, we present results separately for the periods 1979-83, 1984-92, and 1993-6.

We found 7796 deaths from dementias and neurodegenerative disorders for study. The commonest diagnoses were senile and presenile dementias (2074 deaths), cerebral degenerations (1924), and extra-pyramidal disorders (1797). During 1979-83 (1628 deaths) directly standardised mortality changed little, being 10.4 and 10.0 per million in 1979 and 1983 respectively (figure). Between 1984 and 1992 (4574 deaths), when the population was first known to have been exposed to BSE infected material, mortality decreased from 17.0 to 14.7 per million. During 1993-6 (1594 deaths), mortality increased from 11.1 per million in 1993 to 13.3 in 1995 before falling to 12.6 in 1996."

"For statistical analysis, we split the study period into four groups (1979-83, 1984-7, 1988-92, 1993-6). Analysis of covariance was done with mortality as the dependent variable and group, year, and group?year interaction as factors. This enabled us to estimate separate slopes for each group. The interaction was significant (P=0.03), suggesting that the slope of rate against time had changed over the study period. The only positive slope was between 1993 and 1996 (slope=0.53, 95% confidence interval 0.03 to 1.04)."

"Research is also under way to identify any cases of Creutzfeldt-Jakob disease that may have been missed in people aged under 45 dying from a dementing illness during 1979-96."

Comment: This is an independent estimate of the upper bound of possible missed cases of nvCJD. Particular missed cases were asserted recently by Narang. Arbitrarily attributing the increase from 1993-6 entirely to nvCJD, holding other dementia rates fixed, and using the authors' fitted slope on a population of 43,081,000 with 1594 dementia deaths, this works out to 68 cases, roughly 3x the number of confirmed cases. So even if some cases have been missed, the overall number remains low and unsuitable for estimating future cases.

Genomic structure of the bovine PrP gene and complete nucleotide sequence of bovine PrP cDNA.

Anim Genet 1998 Feb;29(1):37-40
Horiuchi M, Ishiguro N, Nagasawa H, Toyoda Y, Shinagawa M
Comment: newly posted to Medline. The journal itself is offline and the abstract minimally informative. The authors have 6 previous entries in GenBank on bovine prion. This one refers to AB001468, dated 27-MAR-1997. It is hard to say what the significance is of a bovine polymorphism 1226 bp downstream of the coding region. There seems to have been no comparison to the recent entire human-sheep-mouse sequences by Lee et al. for which no article has yet appeared.

Unfortunately, the retrotransposon analysis software cited by Lee et al. is not available online in any practical sense to be applied to bovine [and hamster] though perhaps it was done in the body of this new article. If not, it might be mostly doable by comparison with sheep. The interest would be in how fast garbage is accumulating in eukaryotic lineages.

     sequenced:        1..4244 Holstein-Friesian cow
     5'UTR             1..161
     CDS               162..956
     3'UTR             957..4244
     D10612           2096 replace="g"
     variation        2182 replace="A"
     misc_signal      4003..4011 AU-rich elementthought to mediate mRNA degradation
     polyA_signal     4207..4212
     polyA_signal     4222..4227
The present authors previously reported the nucleotide sequence of the 5' half of a cDNA encoding bovine prion protein (PrP) and the genomic structure of the bovine PrP gene encoding the 5' -untranslated region. Here they report the extent of intron 2 of the bovine PrP gene and the nucleotide sequence of the 3' half of bovine PrP cDNA that had not been determined before. This newly sequenced 3' half of the bovine PrP cDNA consisted of 2149 bp. The entire 3'-untranslated region (3'-UTR) was found to be encoded by a single exon, exon 3. One nucleotide polymorphism was found in the 3'-UTR. The length of intron 2 was estimated to be about 14 ,000 bp. The structure of bovine PrP gene can be defined by combining the present results and previous reports on the bovine PrP gene.
       Bovine PrP gene for prion protein, exon 3 (partial)
       gi|442464|dbj|D26151|BOVPRPB [442464]

       Bovine PrP gene for prion protein, promoter region (exon 1 and exon 2)
       gi|442463|dbj|D26150|BOVPRPA [442463]

       Bovine PrP gene encoding prion protein
       gi|217597|dbj|D10614|BOVPRP3 [217597]

       Bovine PrP gene encoding prion protein
       gi|217595|dbj|D10613|BOVPRP2 [217595]

       Bovine mRNA for prion protein
       gi|217593|dbj|D10612|BOVPRP1 [217593]

       Bovine mRNA for prion protein, complete cds
       gi|1888342|dbj|AB001468|AB001468 [1888342]

Design of peptides undergoing self-catalytic alpha-to-beta transition and amyloidogenesis.

Biopolymers 1998;47(1):83-92 
Mihara H, Takahashi Y, Ueno A
Improved understanding of amyloidogenic peptides and proteins such as prion proteins and Alzheimer's beta peptides has attracted much attention to the elucidation of the molecular mechanisms of such amyloidogenesis. As a representative, in the prion protein, the conformational transitions from alpha-helix to beta-structure undergo along with the amyloidogenesis in a self-catalytic manner. Moreover, recent studies by the de novo design of peptides and proteins as well as the amyloidogenesis of peptides and proteins including pathogenic protein mutants have provided insight into the conformational changes essential to amyloidogenesis and correct folding.

Molecular Evolution in Relation to Spongiform Disease

J Mol Evol 1998 Aug;47(2):133-145 Krakauer DC, de A Zanotto PM, Pagel M
Modification of the cellular prion protein has been correlated with the acquisition of several neurodegenerative diseases, including kuru, scrapie, bovine spongiform encephalopathy (BSE), and Creutzfeldt-Jakob disease (CJD). Sequence conservation and amino acid identity are known to influence the efficacy of interspecific transmission. We analyzed patterns of interspecific genetic variation with a view toward identifying features related to disease transmission. The reconstructed gene trees and amino acid tree were compared with the species tree, and all discordances observed were related to the species barrier of disease transmission. The rates of synonymous substitution, nonsynonymous substitution, and nucleotide content were determined for the protein-coding gene. Substitutions implicated in each of the prion diseases were found to occur in regions of the protein that are least variable across all species-opposite to the pattern of variability expected from interaction with an infectious pathogen. Amino acid residues related to the species barrier form a single cluster associated with the first alpha-helical domain of the protein. Residues related to sporadic and hereditary human prion disease form two separate clusters, associated with the second and third alpha-helical domains. Taken together, these results are consistent with the view that prion diseases arise from accidents in protein folding, rather than infection with an undiscovered virus-like particle. We speculate that the differences in disease phenotype between transmissable and hereditary forms could result from interactions between different parts of the protein during propagation.

Dapsone to delay symptoms in Creutzfeldt-Jakob disease

 Lancet Volume 352, Number 91268 August 1998 
Laura  Manuelidis, William Fritch, Igor Zaitsev
Recent experiments with a rat-adapted CJD agent have shown that brain microglia (antigen-presenting cells of myeloid lineage) and astroglia are activated as early as 150 days after infection while function is comprised only after more than 300 days. Vaccination effects in CJD also implicate inflammatory cells in processing the infective agent and suppression of more virulent strains. Radiation and cyclophosphamide, which affect rapidly dividing B and T cells but not long-lived macrophages, microglia, or astrocytes, have had no effect on scrapie incubation, although compounds which target macrophages can prolong or even abolish peripheral infections.

We tested the effects of indometacin and dapsone, anti-inflammatory drugs which enter the brain after being taken by mouth....Dapsone has been used to subdue organisms that hide in macrophages. Dapsone may also decrease amyloid formation. ... These results suggest that dapsone may delay symptomatic progression in patients in the early clinical stages of disease, even when pathological PrP has begun to form. Because PrP itself has been incapable of reproducing infections, and Congo Red embedded in slow release polymers in the brain does not prolong CJD (unpublished), we suspect dapsone may alter macrophage processing of a still undefined infectious agent. Dapsone may also modulate diffusible inflammatory factors that compromise neuronal function.

What the dentist needs to know about TSEs

Quintessence Int 1998 May;29(5):319-321
Gonzales TS, Rushing EJ
...Risk for exposure to prion disease is exceedingly remote in the dental practice and that current universal infection control procedures are probably sufficient.

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