Type 3 collagen

• utilizes lysine residues
• reacted with complement C5 where
• Type 3 collagen inlays with type 1 in hair, [speculation: then called type 5]

My thinking

how is it possible that the protein fibers in collagen are made extracellulary when DNA is only intracellular?

• type 3 collagen could be made extracellular by fungi
• attacked by immune complement C5 to inhibit the fungal viability
• collagen proteins would be made intracellular if they were made via human DNA

Tendons have very little blood flow because they are remnants of fungal fibers

Hence, tendons are very difficult to regrow or heat as compared to soft tissues.

Notes to self. Re-watch Complement lecture; C1 > C4 > C2 > C3 > C5 > C6, C7, C8, [C9] to digest bacterial cell walls, C5 can attach to macrophages for direct internalization, of the complements the C4b (body) attaches to release C4a, an arginine rich complex that directionally attaches to neutrophils as a guide to the direction to travel by the arginine producing nitric oxide as a 3 cell layer of vasodilation, opening the doorways to facilitate travel. oxygen is provided by the cell, might be as a peroxide released by glutathione peroxidase enzymes.

Immune complement attacks germs, possible that type 3 collagen is a result of immune attacks on germs to form structure.

The five most common types of collagen are:

1. Type I: skin, tendon, vasculature, organs, bone (main component of the organic part of bone)
2. Type II: cartilage (main collagenous component of cartilage)
3. Type III: reticulate (main component of reticular fibers), commonly found alongside type I
4. Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane
5. Type V: cell surfaces, hair, and placenta, [found alongside type 1]

Type 1 collagen

• scar tissue, end product when tissue heals by repair
• tendons,
• ligaments,
• the endomysium of myofibrils,
• the organic part of bone,
• the dermis,
• the dentin
• organ capsules.

Type 2 collagen

• cartilage,
• heals much easier and faster than tendons (type 3)

Type 3 collagen

• Complement system C5 is involved in type 3 collagen
  
  • homotrimer, a protein composed of three identical peptide chains (monomers),
  • each called an alpha 1 chain of type III collagen
  • Formal name: collagen type III, alpha-1 chain
• one of the fibrillar collagens whose proteins have
  • long
  • inflexible [rigid, like the Achilles tendon]
  • triple-helical domain
• First,
  • about 145 of the 239 triple-helical domains are hydroxylated to 4-hydroxyproline by prolyl-4-hydroxylase.
• Second,
  • some of the lysine residues are hydroxylated or glycosylated, or
  • some lysine as well as hydroxylysine residues, to
    • undergo oxidative deamination catalysed by lysyl oxidase.
  • lysine is high in whey protein (skim milk) and gram positive bacteria
• Type 3 collagen is high in reticular fibers
  • reticular fibers are found in BPH - Benign Prostatic Hyperplasia (swollen prostate)

Type 4 collagen

Type 5 collagen

• Hair
• Placenta

Technical Reference--- Chemoattractant, attracts cells such as neutrophils

--- My thinking is that the extracellular laying down of non-flexible fibers is initially done by fungi, then attacked by C5 complement to inhibit further fungal growth [eg. Achilles tendon].

Chemotactic Peptide/Complement Receptors

E.R. Prossnitz, L.A. Sklar, in Encyclopedia of Biological Chemistry (Second Edition), 2013

C5a

The anaphylatoxin C5a, the most potent plasma-derived chemotactic factor, is a 74-amino-acid peptide/protein released from the α-chain of C5 by either the classical or alternative pathway C5 convertases. Structurally, the protein consists of four antiparallel α-helices held together by disulfide bonds and an 11-amino-acid carboxy terminal tail. Unlike the small formyl peptides, C5a appears to interact with its receptor at two sites. The α-helical bundle interacts with the receptor's amino-terminal domain, whereas the tail appears to insert itself into the transmembrane bundle of the receptor, thereby activating the receptor. Synthetic peptides representing the carboxy-terminal ten amino acids are full agonists, though with potencies 1000–10 000 lower than C5a itself. The sequence Gln–Leu–Gly–Arg is a highly conserved effector sequence in C5a from numerous species. Substitution of residues within this region can greatly augment potency. Removal of the final arginine residue in C5a results in greatly decreased potency, ranging from 1000-fold decrease for spasmogenic activity to 10-fold for chemotactic activity.

--->  C5a receptors are selective over C3a complement and stimulated by ASP

Acylation Stimulating Protein (ASP)

Eiji Ota, in Handbook of Hormones, 2016
Receptors
Structure and Signal Transduction Pathway

Complement component 5a receptor 2 (C5L2, also known as GPR77) is considered to be a functional receptor of ASP. [ASP - Acylation Stimulating Protein] ASP and its carboxy-terminal peptides do not bind to or activate the C3a receptor. C5L2 is highly expressed in adipose tissues, heart, liver, lung, spleen, bone marrow, and leukocytes. C5L2 consists of approximately 340 aa residues and contains an N-terminal extracellular domain, seven transmembrane domains and a C-terminal intracellular domain. C5L2 shows high homology with the C5a receptor (C5aR). However, C5L2 does not have the aspartic acid–arginine–phenylalanine (Asp–Arg–Phe) (DRF) motif due to the substitution of arginine with leucine. Therefore, C5L2 is considered to be a decoy receptor of C5aR [4]. However, C5L2 is considered to be a functional receptor, and the transduction pathway is not understood in detail because of this. An idea has emerged that C5L2 mediates a G protein-independent signaling pathway, such as β-arrestin signaling. After stimulation with C5a, C5a desArg, C3a, or C3a desArg, β-arrestin 1-GFP fusion protein was translocated to human C5L2 in transfected HEK293 cells [5].

--->  β-arrestin signaling

A New Era of Catecholamines in the Laboratory and Clinic

Andrew C. Emery, in Advances in Pharmacology, 2013
3.4 Arrestin assays

β-Arrestin-mediated endocytosis appears to be a fairly common phenomenon among different GPCRs, at least those for catecholamines. In addition, β-arrestins have been shown to act as physiologically relevant signaling molecules for many GPCRs across various cell and tissue systems. Therefore, assays of β-arrestin activity can serve as an index of GPCR desensitization for agonist detection. Of increasing importance, β-arrestin-based assays also serve the purpose of discovering novel biased ligands and explaining to what extent known ligands are biased. Once a GPCR of interest is confirmed to be regulated by β-arrestin, cellular imaging assays are commonly used to measure GPCR-dependent translocation of an exogenously expressed fluorophore-tagged β-arrestin. As an alternative to whole-cell imaging to measure β-arrestin activity, numerous biochemical assays have come into wide use. These assays generally require a cell line coexpressing a fluorophore-tagged GPCR of interest and a luciferase-tagged β-arrestin. Upon GPCR-β-arrestin interaction, a BRET (bioluminescence resonance energy transfer) signaling is generated by proximity of the two tags. Reporter gene-based assays for β-arrestin activity are also available. One such assay makes use of coexpression of a β-arrestin–protease fusion protein and a recombinant GPCR of interest connecting to a transcription factor via a specific protease recognition site. Thus, upon GPCR–arrestin interaction, a transcription factor is liberated to enhance the expression of a reporter gene product.

--->  Serine protease of pancreatic trypsin-like specifically digests lysine away from arginine

complement C5a can enter the C5aR (R-receptor) or the C5L2 receptor as a means to manufacture extracellular connective tissue type 3.

---> β-arrestin 1,  β-Arrestin 2

The Molecular Biology of Arrestins

Dianhua Jiang, ... Paul W. Noble, in Progress in Molecular Biology and Translational Science, 2013
4 β-Arrestins and Structural Cells

β-Arrestins are expressed in epithelial cells,65,66 endothelial cells,22,67,68 and smooth muscle.22 β-Arrestin 1 has been found to be expressed in human endothelial cells and smooth muscle cells.22 In these cells, β-arrestin 1 expression can be upregulated by cAMP-inducing agents such as cholera toxin, forskolin, iloprost, and isoproterenol. 22 β-Arrestins mediate the infections of Streptococcus pneumonia 67 and Neisseria meningitidis 69 through interactions with endothelial cells. β-Arrestin 2 regulates thrombin–PAR1 signaling in endothelial cell adhesion.68

β-Arrestin influences CXCL12-mediated epithelial cell migration. CXCL12-stimulated cell migration is enhanced by CXCR7/CXCR4 coexpression in a β-arrestin-dependent manner.65 In a CXCR4/CXCR7-expressing MDA-MB-231 breast cancer epithelial cell line, inhibition of β-arrestin using either siRNA knockdown or a dominant negative mutant suppressed CXCL12-induced cell migration.65