The Pacific electric ray and its relatives are used as model organisms for biomedical research, because their electric organs contain an abundance of important nervous system proteins such as nicotinic acetylcholine receptor and acetylcholinesterase.
For example, TraK analogs (CLK_A0294; CLJ_A0213) and TraG/D (CLK_A0293; CLJ_A0212) flanked by hypothetical ORFs, as well as genes that encode for putative type II and type IV secretion system proteins, such as pili, have been described.
Similarly, the precise role of protein folding and stabilization proteins in A. pleuropneumoniae has not been reported, but in other systems, proteins such as HtpG and HtpX are usually up-regulated during stress such as nutrient deprivation and their down-regulation is consistent with BALF being a comparatively non-stressful environment [97], [98].
Tumors are potential sources of ligands for innate immune system pattern recognition receptor proteins, such as toll-like receptors (TLRs), nucleotide oligomerization domain- (NOD-) like receptors, retinoic acid-inducible gene-1 (RIG-1), and melanoma differentiation-associated protein-5 (MDA-5) helicases [ 53].
These can activate a series of second messenger system proteins that can coordinate processes such as neurotransmitter release in nerve cells and release of hormones in endocrine cells.
Conversely, category V is enriched with ATP-binding cassette (ABC) transporter system proteins related to defense mechanisms, such as the M. hyorhinis ABC-type multidrug-like transport system ATP-binding proteins and their orthologs in M. flocculare and M. hyopneumoniae.
Such toxin antitoxin system proteins play a role in mediating stability of plasmids by imposition of an addiction mechanism to the host (Arcus et al. 2005).
However, finding a suitable recombinant production system for proteins such as full-length human IGFBPs, still remains a challenge.
Similar systems that are widespread among gram-negative bacteria such as E. coli, Serratia marcescens and Pseudomonas aeruginosa form a specialized secretory system for proteins, such as pore-forming toxins, proteases, lipases and S-layer proteins [ 31].
This is a quite interesting issue as several viruses use the ubiquitin proteasome system to destabilize proteins, such as IRF3 and STAT proteins, that are important for transcription of Interferon and Interferon-stimulated genes [ 42].
At this stage the pathogen uses a specialized secretion system to deliver virulence proteins, such as AvrPto and AvrPtoB, into the plant cell.
