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1.  Prion protein self-peptides modulate prion interactions and conversion 
BMC Biochemistry  2009;10:29.
Background
Molecular mechanisms underlying prion agent replication, converting host-encoded cellular prion protein (PrPC) into the scrapie associated isoform (PrPSc), are poorly understood. Selective self-interaction between PrP molecules forms a basis underlying the observed differences of the PrPC into PrPSc conversion process (agent replication). The importance of previously peptide-scanning mapped ovine PrP self-interaction domains on this conversion was investigated by studying the ability of six of these ovine PrP based peptides to modulate two processes; PrP self-interaction and conversion.
Results
Three peptides (octarepeat, binding domain 2 -and C-terminal) were capable of inhibiting self-interaction of PrP in a solid-phase PrP peptide array. Three peptides (N-terminal, binding domain 2, and amyloidogenic motif) modulated prion conversion when added before or after initiation of the prion protein misfolding cyclic amplification (PMCA) reaction using brain homogenates. The C-terminal peptides (core region and C-terminal) only affected conversion (increased PrPres formation) when added before mixing PrPC and PrPSc, whereas the octarepeat peptide only affected conversion when added after this mixing.
Conclusion
This study identified the putative PrP core binding domain that facilitates the PrPC-PrPSc interaction (not conversion), corroborating evidence that the region of PrP containing this domain is important in the species-barrier and/or scrapie susceptibility. The octarepeats can be involved in PrPC-PrPSc stabilization, whereas the N-terminal glycosaminoglycan binding motif and the amyloidogenic motif indirectly affected conversion. Binding domain 2 and the C-terminal domain are directly implicated in PrPC self-interaction during the conversion process and may prove to be prime targets in new therapeutic strategy development, potentially retaining PrPC function. These results emphasize the importance of probable PrPC-PrPC and required PrPC-PrPSc interactions during PrP conversion. All interactions are probably part of the complex process in which polymorphisms and species barriers affect TSE transmission and susceptibility.
doi:10.1186/1471-2091-10-29
PMCID: PMC2789745  PMID: 19943977
2.  Mapping of possible prion protein self-interaction domains using peptide arrays 
BMC Biochemistry  2007;8:6.
Background
The common event in transmissible spongiform encephalopathies (TSEs) or prion diseases is the conversion of host-encoded protease sensitive cellular prion protein (PrPC) into strain dependent isoforms of scrapie associated protease resistant isoform (PrPSc) of prion protein (PrP). These processes are determined by similarities as well as strain dependent variations in the PrP structure. Selective self-interaction between PrP molecules is the most probable basis for initiation of these processes, potentially influenced by chaperone molecules, however the mechanisms behind these processes are far from understood. We previously determined that polymorphisms do not affect initial PrPC to PrPSc binding but rather modulate a subsequent step in the conversion process. Determining possible sites of self-interaction could elucidate which amino acid(s) or amino acid sequences contribute to binding and further conversion into other isoforms. To this end, ovine – and bovine PrP peptide-arrays consisting of 15-mer overlapping peptides were probed with recombinant sheep PrPC fused to maltose binding protein (MBP-PrP).
Results
The peptide-arrays revealed two distinct high binding areas as well as some regions of lower affinity in PrPC resulting in total in 7 distinct amino acid sequences (AAs). The first high binding area comprises sheep-PrP peptides 43–102 (AA 43–116), including the N-terminal octarepeats. The second high binding area of sheep-PrP peptides 134–177 (AA 134–191), encompasses most of the scrapie susceptibility-associated polymorphisms in sheep. This concurs with previous studies showing that scrapie associated-polymorphisms do not modulate the initial binding of PrPC to PrPSc. Comparison of ovine – and bovine peptide-array binding patterns revealed that amino acid specific differences can influence the MBP-PrP binding pattern. PrP-specific antibodies were capable to completely block interaction between the peptide-array and MBP-PrP. MBP-PrP was also capable to specifically bind to PrP in a Western blot approach. The octarepeat region of PrP seems primarily important for this interaction because proteinase K pre-treatment of PrPSc completely abolished binding.
Conclusion
Binding of MBP-PrP to PrP-specific sequences indicate that several specific self-interactions between individual PrP molecules can occur and suggest that an array of interactions between PrPC-PrPC as well as PrPC-PrPSc may be possible, which ultimately lead to variations in species barrier and strain differences.
doi:10.1186/1471-2091-8-6
PMCID: PMC1855927  PMID: 17430579

Results 1-2 (2)