Cell–cell recognition

[2] Like other cellular functions, cell–cell recognition is impacted by detrimental mutations in the genes and proteins involved and is subject to error.

The biological events that unfold due to cell–cell recognition are important for animal development, microbiomes, and human medicine.

Cell–cell recognition occurs when two molecules restricted to the plasma membranes of different cells bind to each other, triggering a response for communication, cooperation, transport, defense, and/or growth.

Rather than induce a distal response, like secreted hormones may do, this type of binding requires the cells with the signalling molecules to be in close proximity with each other.

[3] The molecules that complete this binding consist of proteins, carbohydrates, and lipids, resulting in a variety of glycoproteins, lipoproteins, and glycolipoproteins.

[8] One type of PRR is a group of integral membrane glycoproteins called toll-like receptors (TLRs), which can recognize certain lipoproteins, peptidoglycan, CpG-rich DNA, and flagellar components in bacterial cells, as well as glycoproteins and phospholipids from protozoan parasites and conidia (fungal spores).

[8] The binding of PAMPs to TLR proteins generally results in an internal signaling cascade including a number of phosphorylations, the adding of a phosphate group, and ubiquitinations, the adding of a small protein that marks molecules for degradation, that eventually leads to the transcription of genes related to inflammation.

Mutations in mammalian receptor proteins can cause disorders in cell–cell recognition, increasing individual susceptibility to certain pathogens and chronic conditions.

When mutations occurs in genes that code for TLRs, the proteins can lose the ability to bind with polysaccharides, lipids, or proteins on the cell wall or membrane of single-celled pathogens, resulting in a failure of the innate immune system to respond to infection that allows disease to develop rapidly.

[14] An Arginine to Glutamine mutation in TRL2, Arg753Gln, was connected to increased pediatric Urinary Tract Infections caused by gram-positive bacteria.

[17] The common characteristic between these missense mutations is that the amino acid residues that are substituted have notably different side chain properties, which likely contributes to the defective TLR protein function.