Abusing GRAS #4
Matrix Metalloproteinases, The Furin Cleavage Site, and Dysbiosis
Hello Friends, in this article we will connect the microbiome to the metalloprotease formation of tight junctions in the epithelium of the gut walls via the upregulation of Matrix Metalloproteinases (MMPs). Now that we have a basic understanding of how the main attraction of these articles are the building blocks for tissues we can explore exactly how the microbiome guides, through cis/trans conformation the healthy and proper function of tight junction fitness.
Of course, none wish to have a leaky gut, and hopefully we are all now aware that all we must do to make ours so is to eat sugar, wheat, and dairy loaded with microbiota destroying “preservatives” that fall under “ingredient” regulatory codes like EDTA and Triclosan. While we were able to get one banned the other, EDTA, is still destroying gut and oral lactic acid bacteria at a commercial scale with it long being known (2013) that only a very short “exposure time” is “necessary for EDTA to inactivate endogenous MMP activity in human dentin” [1]
Microbiome guides many functions but the importance of conformation of the cis/trans face of the Golgi Apparatus products are our focus here. Its not commonly known that many of our bodies’ proteins go through dramatic reshaping after being manufactured by specific cells or tissues. One way to think about this process is in how the body can build and reshape primary products into secondary ones via post conformation. For example the hemopexin-like C-terminal domain is a common subunit that can be reshaped and scaffolded in post translation: “the C-terminal domain has structural similarities to the serum protein hemopexin. It has a four-bladed β-propeller structure. β-Propeller structures provide a large flat surface that is thought to be involved in protein-protein interactions. This determines substrate specificity and is the site for interaction with TIMP's (tissue inhibitor of metalloproteinases). The hemopexin-like domain is absent in MMP-7, MMP-23, MMP-26, and the plant and nematode. The membrane-bound MMPs (MT-MMPs) are anchored to the plasma membrane via a transmembrane or a GPI-anchoring domain.” [2]
If you are wondering what that means, it’s actually very simple because it’s about localization. The basic building block can make a variety of things but it’s the post conformations that direct/localize the block to the building site or in this case for the desired tissue construction or destruction.
Let me make another example that should get your attention. One of the specific functions of the microbiome conformation process is to recognize tight junction forming metalloproteinase with a Furin-Cleavage site. [2] As we recall from the pandemic, people with dysbiosis suffered at much greater rates than those without as the virus recruited native commensal bacteria MMP Furin sites via its gain of function pathology. “The S protein of SARS-CoV-2 binds to the ACE2 receptor and is activated by protease activity of host Furin or TRMPSS2 that cleave S protein subunits to promote viral entry.” [3] I bet you didn’t expect that!
In this case Cov19 utilized mobile genetic elements with matrix metalloproteinases that are manufactured as inactive zymogens (pro-MMPs) that require activation via commensal post translation before they can function. The pro-peptide domain contains a 'cysteine switch' mechanism that regulates enzyme activity in said commensal oral bacteria. When the Cov19 virus hijacked this machinery, it began the over production of growth/cystine promoting MMPs. Specifically, “there is increasing evidence to suggest that a dysregulation of the protease/antiprotease balance in the gut contributes to epithelial damage and increased permeability. Excessive proteolysis leads to direct cleavage of intercellular junction proteins, or to opening of the junction proteins via activation of protease activated receptors.” [4]
A conserved cysteine residue in the pro-domain interacts with the zinc ion in the active site. This interaction prevents substrate binding and cleavage, maintaining the enzyme in its inactive form. In most MMPs, this cysteine residue is located within the highly conserved sequence PRCGxPD. Activation occurs when the pro-domain is removed, or the cysteine-zinc interaction is disrupted.
Some MMPs contain a prohormone convertase, which is considered Furin-like, cleavage site in this domain. When cleaved by these enzymes, the MMP becomes active and MMP-23A and MMP-23B which have a very unique, and highly conserved trait in nature, that they include a transmembrane segment within their pro-peptide domain. This zymogen activation mechanism serves as a rarified regulatory checkpoint that specifically obligates that proteolytic activity occurs only at appropriate times and locations within tissues because of these cis/trans commensal conformation systems.
in part four we now see how MMPs directly affect tight junctions in a commensal way to keep you, and your microbiome, in peak fitness. I used the example of cov19 hijacking the native Furin cleavage site via mobile genetic elements regulated directly by post translation in oral corynebacterium. In the next article we will go over ADAM’s (a disintegrin and metalloproteinase) and Extended-Spectrum β-Lactamases (ESBL) as we get closer to manufacturing a probiotic that can be used to address the issues I’m raising.
[1] J Endod. Author manuscript; available in PMC: 2013 Jan 1.
Published in final edited form as: J Endod. 2011 Nov 3;38(1):62–65. doi: 10.1016/j.joen.2011.09.005
Inhibition of endogenous dentin matrix metalloproteinases by ethylenediaminetetraacetic acid
https://pmc.ncbi.nlm.nih.gov/articles/PMC3240849/
[2] Matrix metalloproteinase
https://en.wikipedia.org/wiki/Matrix_metalloproteinase
[3] Rev Med Virol 2024 May;34(3):e2543. doi: 10.1002/rmv.2543.
SARS-CoV-2, periodontal pathogens, and host factors: The trinity of oral post-acute sequelae of COVID-19
https://pubmed.ncbi.nlm.nih.gov/38782605/
[4] World J Gastroenterol. 2017 Mar 28;23(12):2106-2123. doi: 10.3748/wjg.v23.i12.2106.
Regulation of intestinal permeability: The role of proteases