Prion Driven Curiosity

While reading about bacteriocins, my topic of interest for my PhD project, I was reminded of another deadly protein particle that I was interested in during my early undergraduate career. I was intrigued with protein pathogens called, prions. Prions are both infectious pathogens and genetic diseases which have devastating effects on mammals [2]. These are diseases like Scrapie, mad cow disease, and Kuru. “Prions are devoid of nucleic acid and seem to be composed exclusively of a modified isoform of prion protein (PrP) designated PrPSc. The normal, cellular PrP, denoted PrPC, is converted into PrPSc through a process whereby a portion of its α-helical and coil structure is refolded into β-sheet. [1]” Basically, all this is saying is prions are proteins that get misfolded using a specific mechanism. My short-lived obsession began when I a book called, “The family that Couldn’t Sleep: A medical mystery” by D. T Max. The book highlights an Italian family that is cursed with a genetic prion disease called fatal familial insomnia. A disorder that tortures its host with the inability to fall asleep until the lack of sleep eventually kills the host. When I found out that a protein can be genetically or pathogenically motivated to misfold your brain proteins, I saw a whole new dimension to the world. My 20-year-old-self quickly spiraled into an existential crisis contemplating the complexity and vastness of the world.

While reading about bacteriocins, I began to wonder if they had any known connections to prions. After all, many recorded characteristics of certain bacteriocins overlap with prions. Like prions, bacteriocins are proteinaceous, small, and some are recorded to be extremely stable. If you are wondering what bacteriocins are according to Wikipedia they are proteinaceous or peptidic toxins produced by bacteria to inhibit the growth of similar or closely related bacterial strain(s). In my simple definition, they are proteins that are encoded by bacteria to fight off other bacteria, usually closely related bacteria. You can think of them as proteins that act sort of like antibiotics for the purposes of this story. With my curiosity in full swing, I came across a paper examining striking similarities between prions and the bacteriocin, Microcin E492. This paper was titled, “Prion-like characteristics of the bacterial protein Microcin E492[5]”. This paper highlights sequence similarities among prions and Microcin E492. The study found a prion-like method to regulating protein functions in Microcin E492. The paper touches on previous work that examines the ability of proteins to self-propagate and transmit biological information has been shown to be beneficial in yeast. It also points out, prion like protein confirmation changes have been shown to be beneficial to the antiviral response in mammals.

With bacteriocins having prion-like characteristics, and multiple recorded prion-like regulating systems interacting intimately with a vast array of biological life, I wanted to figure out information on the connections they may have with the plant world. I was lead to a science direct article titled, “Grass Plants Bind, Retain, Uptake, and Transport Infectious Prions” [3]. This study found evidence that prions were able to bind and replicate on plant roots and leaf surfaces. They were then found to transmit infectious the prion to animals that consumed the plant. This incorporated plants as vectors of mammalian pathogenic prions. The next bit of information I found interesting I found in a study titled, “Luminidependens (LD) is an Arabidopsis protein with prion behavior [4]” This paper alludes to the possibility of Luminidependens (LD), a protein in plants that regulates when a plant will flower, has prion-like traits. It emphasizes the LD protein has a sequence that is strikingly similar to prion sequences in yeast. The paper explains that the LD prion-like domain enters into a structure and initiates a change in function of an associated protein domain in a stable and heritable way. This may be the mechanism for how plants are seemingly able to remember environmental and abiotic factors. Plant prion-like proteins could very well play an important role in plant evolution and be a key in understanding plasticity in plants. The paper is unable to positively confirm that LD protein serves as a prion, but it does hint that there is now evidence that it may. Propagation of functional prions may be found to be an important to many types of life and understanding them could lead to novel discoveries across many biological fields. Prions are rampant in the environment and may be manipulating microbiomes all over the biosphere.

Freestyle Citations

[1] Conversion of alpha-helices into beta-sheets features in the formation of the scrapie prion proteins. Pan KM, Baldwin M, Nguyen J, Gasset M, Serban A, Groth D, Mehlhorn I, Huang Z, Fletterick RJ, Cohen FE Proc Natl Acad Sci U S A. 1993 Dec 1; 90(23):10962-6.

[2] Molecular biology of prion diseases. Prusiner SB Science. 1991 Jun 14; 252(5012):1515-22.

[3] Sandra Pritzkow, Rodrigo Morales, Fabio Moda, Uffaf Khan, Glenn C. Telling, Edward Hoover, Claudio Soto, Grass Plants Bind, Retain, Uptake, and Transport Infectious Prions, Cell Reports, Volume 11, Issue 8, 2015,Pages 1168-1175, ISSN 2211-1247, https://doi.org/10.1016/j.celrep.2015.04.036.

[4] Sohini Chakrabortee, Can Kayatekin, Greg A. Newby, Marc L. Mendillo, Alex Lancaster, Susan Lindquist. Luminidependens (LD) is an Arabidopsis protein with prion behavior. Proceedings of the National Academy of Sciences, 2016; 201604478 DOI: 10.1073/pnas.1604478113

[5] Prion-like characteristics of the bacterial protein Microcin E492. Shahnawaz M, et al. Sci Rep. 2017.

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