User:Immcarle196/Pathogen-associated molecular pattern

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Pathogen-associated molecular patterns (PAMPs) are small molecular motifs conserved within a class of microbes. These PAMPs are usually encode parts of the organism vital to survival, thus hard to modify, and are not present in the host. They are recognized by toll-like receptors (TLRs) and other pattern recognition receptors (PRRs) in both plants and animals. A vast array of different types of molecules can serve as PAMPs, including glycans and glycoconjugates.

Common PAMPs
Bacterial lipopolysaccharides (LPSs), also known as endotoxins, are found on the outer cell membranes of gram-negative bacteria, are considered to be the prototypical class of PAMPs. The lipid portion of LPS, lipid-A, is the diglycolamine backbone with multiple acyl chains and is usually the conserved structural motif that is recognized by TLR4, particularly the TLR-MD2 complex, Microbes can nuse 2 strategies to avoid detection, either masking of Lipid A to prevent immune recognition or directing LPS toward an immunomodulatory receptor.

Flagellin is also another PAMP that is recognized via the constant domain, D1 by TLR5. Despite being a protein, its N- and C- terminal ends are highly conserved, due to its necessity for function of flagella. Lipoteichoic acid (LTA) from gram-positive bacteria, peptidoglycan (PG), bacterial lipoproteins (sBLP), a phenol soluble factor from Staphylococcus epidermidis, LPS from porphyromonas gingivitis, and glycosylphosohotidylinotol lipiosd from trypanosoma cruzi, and a component of yeast walls called zymosan, are all recognized by a heterodimer of TLR2 and TLR1 or TLR6. However, LTAs result in a weaker pro-inflammatory response compared to lipopeptides, as they are only recognized by TLR2 instead of the heterodimer. Double-stranded RNA (dsRNA), a universal viral PAMP, is recognized by TLR3. CpG motifs, found in bacterial DNA, need to be internalized to be recognized by TLR9. Viral glycoproteins, as seen in the viral-envelope, as well as fungal PAMPS on the cell surface or fungi are recognized by TLR2 and TLR4.

History
First introduced by Janeway in 1989, PAMP was used to describe microbial components that would be considered foreign in a multicellular host. The term "PAMP" has been criticized on the grounds that most microbes, not only pathogens, express the molecules detected; the term microbe-associated molecular pattern (MAMP), has therefore been proposed. A virulence signal capable of binding to a pathogen receptor, in combination with a MAMP, has been proposed as one way to constitute a (pathogen-specific) PAMP. Plant immunology frequently treats the terms "PAMP" and "MAMP" interchangeably, considering their recognition to be the first step in plant immunity, PTI (PAMP-triggered immunity), a relatively weak immune response that occurs when the host plant does not also recognize pathogenic effectors that damage it or modulate its immune response.