What is a Prion?
Prisons are naturally produced proteins in the brain of animals and humans. These proteins are usually harmless and functional with different pathways of action.However, after some deformation or interaction with deformed proteins, they can cause devastating and incurable diseases such as bovine spongiform encephalopathy (sick cow disease) or Jakob-Creutzfeldt disease in people. [1]These agents can propagate within the same host, which causes spongitic lesions and give it the ability to transmit from host to host with high incubation times.Prisons often relate to viruses or viroids, but differ in various things like they are only proteins, which makes them resistant to treatments focused on inactivating nucleic acids.They also have a certain variability within themselves, presenting relevant differences in the lesion pattern and incubation time.Another notable thing is how its infective capacity is limited by species barriers, i.e. that the infection can only be transmitted when there is high protein homology.To exemplify this point, a human would not be infected by eating contaminated tissue from goat or sheep, only the contagion would occur if contaminated tissue of cattle was consumed, due to the homology that exists between human protein and cow. [2]The cell protein of the prion
For a long time, it is unknown exactly what the prions were, and the search for the constituent molecular entity of this agent revealed as a unique component to the PrPSc protein (prion protein) Scarpie). This protein is not of the natural whole, it is a mutation of the PrPC protein.There is still uncertainty about the PrP proteins and their conformational mallability, which largely contributed to their search and research, mainly about the linked genes and regulatory elements that could play an active role in their synthesis. This led to a detailed analysis of the 145 kb of DNA of the human and sheep genes of PrP, seeking preserved regions, ORFs, potential exons, repetitive sequences, possible CpG islands and polymorphic reasons. [2]Regarding its expression, this gene occurs constitutively in neural tissues, such as non-neural tissues, especially in adult animals or humans.The higher levels of this protein are usually detected in neurons of the whole brain, but were mainly detected in the hippocampus. Other places with significant levels of this protein are in the heart and skeletal muscle, but there are also lower levels in most organs except liver and pancreas.The translated product of the RNA is a polypeptide chain of about 250 amino acids, comes to vary with the species, but some notable points are its N-terminal sequence of 22 residues, a series of repetitions of an octapeptide (PHGGWGQ), 4 highly preserved segments and a C-terminal hydrophobic region. The chain undergoes a complex covalent maturation process, which presupposes the proteolytic escision of the peptides signals, the C-terminal addition of glicanfosfatidilnositol (GPI), the formation of an intramolecular disulphur link and, finally, a double glycosylation in the Asn 181 and 197. [2]PrPC is a protein with the ability to specifically bond copper, which gives it an important role in the homeostasis of this cation involved in oxide-reduction processes.The secondary structure of PrPC, solubilized in detergents and in the absence of cations, is mostly helical, while the formation of the complex leads to increased content of extended structures.High-resolution spectroscopic studies with recombinant forms in the absence of ligand have demonstrated that PP consists of two domains, the unstructured N-terminal and the globular C-terminal. As for your cellular metabolism, some translocation studies in vitro Two main topological forms of PP were identified, a form of secretion and two transmembrane forms.The first is transported in vesicles to the cell surface where it is anchored to the membrane. The metabolism of transmembrane forms is not known accurately, but the accumulation above a threshold of forms with the luminal C-terminal correlates with the appearance of neuropathological states. [2]Prison pathology
In prion pathologies, the PrPC cellular protein becomes, by means of post-raductional modifications in an isoform, the so-called protein scrapie or PrPSc. This modification occurs in domains of caveola type, and is characterized by a drastic change of both chemical and physical properties of the protein.These changes bring various characteristics to the new isoform, for example PrPC is soluble in detergents, while PrPSc forms a kind of insoluble amorphous aggregates.Along with this, the cellular form is released from the membrane in soluble form by digestion with PILC, while the form scrapie is not susceptible to enzymatic action, requiring prior denaturing treatment for elimination of GPI, the cellular form is sensitive to proteases and scrapie, On the contrary, it suffers a limited proteolysis generating the truncated form at the extreme N-terminal that aggregates in the form of amyloids and retains infectivity. However, there are also pathological states in which it was not possible to detect PrPSc in terms of resistance to proteases, but the recent description of transmembrane forms could be implicated in these cases. [2]
Post-translational changes of covalent character do not seem to be the direct cause of the conversion process, but rather of its modulation. Thus, the GPI determines the possibility of conversion, as this occurs in specialized domains of membranes where the proteins anchored by GPI are confined.In addition, glycosylation will determine intracellular protein traffic. Something that allowed to establish the structure of scrapie It is spectroscopic studies, and unlike cellular form, this presents as a major element the β chain stabilized in blades and that the amyloid behavior is linked to the presence of β intermolecular blades.This conformational duality of α propeller and β blade appears to be found mainly in the region 106-126, which in the form of synthetic peptide is a powerful neurotoxic. [2]Physiopathology is long and complicated, has multiple presentations, and symptomatology varies according to the present stage of the disease, from the beginning of the disease to a little before the 100 days of suffering is known as the prodromic phase, in which affective symptoms such as insomnia, isolation, hyporexia and weight loss are observed.From the 101 days and until the 200 days are fulfilled, it is known as the intermediate stage or phase, where psychotic symptoms appear as hearing and visual hallucinations, as well as delusional ideas such as feelings of persecution, paranoia and zelotypia.And finally, from the 200 days of suffering, it is the late stage where changes in the conduct arise as a psychomotion, extreme irritability and physical aggression.The presentations of diseases caused by prisons have 3 main presentations, which are divided into hereditaries caused by inherited genetic alterations that facilitate the wrong use of PrPC, the infectious forms that are explained by the interaction of PrPSc on PrPC which causes its transformation to PrPSc and, finally, the sporadic form of the disease that are those that appear without apparent cause and for those that there is no explanation in the present. [3]Diagnostic methods
Finally, the diagnosis of diseases caused by prions in humans is based more than nothing in clinical history and the typical electroencephalography findings, such as high-voltage and slow-wave complexes, on a poorly organized slow-wave background. The findings of cerebral atrophy through imaging studies are another of the main ways to perform a diagnosis, but of low precision.Some other techniques that arose increasing the accuracy and sensitivity of the diagnoses are mainly the immunoanalysis of cerebrospinal fluid, in search of PrPSc.There is also the search for typical pathological characteristics, but these require a cerebral biopsy, on the other hand, the inoculation of samples of the central nervous system in monkeys is a very effective method, but it takes a lot of time and is extremely laborious. [4]Recently, it was demonstrated that in patients with dementia and without acute diseases of the CNS, the detection, by radioinmunoanalysis of protein 14-3-3 in the cerebrospinal fluid strongly supports the diagnosis of diseases caused by prions.Similarly, the detection by two-protein gel two-dimensional electrophoresis, p130/131 allows the diagnosis to be favored when it is added to the accepted clinical criteria. [4]But the search for PrPSc is not the only way to find the pathology, on certain occasions, the detection of early indications or stages can be carried out through the discovery of poorly pleated PrPC protein, which can be achieved through electroforesis or western blot.These findings are based more than nothing on observing differences in molecular weight, comparing samples with the known weight of PrPC that is between 26 and 37 kDa, so results that exceed this range are good indications of the occurrence of diseases caused by prisons. [5]References
- Mayo Clinic, Like the Prisons, [Internet], Mayo Clinic, 2020, [recovered November 24, 2022], available at: https://www.mayoclinic.org/es-es/diseases- conditions/creutzfeldt-jakob-disease/multimedia/normal-and-diseased-prions/img-20007478#:~:text=O%20priones%20son%20son%20prote%C3%ADnas%20,animal%20y%20.
- Gasset M. & Westaway D., The Prisons and their Biology, [Internet], First Ibero-American Virtual Congress of Neurology, 1999, [recovered November 24, 2022], available at: https://www.svneurology. org/congregation/owners -1. html
- Paniz Mondolfi A., Immunopathological aspects of prion infection., Gac Méd Caracas, [Internet], 2005, [recovered November 24, 2022], 113(3), available at: http://ve.scielo. org/scielo. php?script=sci_arttext&pid=S0367-47622005000300004
- Pena I, Prisons and Transmissible Spinopathies: a journey through its history, Revista UNLP, [Internet], 2011, [recovered November 24, 2022], 31(1), available at: https://revistas. unlp.edu.ar/analecta/article/download/12208/11166/41560
- González Miranda E., Adaptation of an in vitro prion propagation system for the mass crib of specific compounds in the face of Human Transmissible Espongiform Encephalopathies, [Internet], University of the Basque Country, 2020, [recovered on 24 November 2022], available at: https://addi.ehu.es/bitstream/handle/10810/50401/Tesis_Ezequiel_Gonzalez_Miranda. pdf?sequence=1
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