Collagen is the most abundant protein in animals. This fibrous, structural protein comprises a right-handed bundle of three parallel, left-handed polyproline II-type helices. Much progress has been made in elucidating the structure of collagen triple helices and the physicochemical basis for their stability. New evidence demonstrates that stereoelectronic effects and preorganization play a key role in that stability. The fibrillar structure of type I collagen—the prototypical collagen fibril—has been revealed in detail. Artificial collagen fibrils that display some properties of natural collagen fibrils are now accessible using chemical synthesis and self-assembly. A rapidly emerging understanding of the mechanical and structural properties of native collagen fibrils will guide further development of artificial collagenous materials for biomedicine and nanotechnology.

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Collagen Structure and Stability

Endothelial Cells in Physiology and in the Pathophysiology of Vascular Disorders

http://www.jbc.org/content/254/19/9933.full.pdf

Laminin--a glycoprotein from basement membranes.

Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks. emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features. At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesins have been reported, and surface plasmin-binding proteins have been defined. The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation.

Pathogenesis of Group A Streptococcal Infections

Tumour cells traverse epithelial and endothelial basement membranes during the successive stages of the metastatic process. At the transition from in situ to invasive carcinoma, local dissolution of the basement membrane is observed microscopically1,2, and coincides with tumour cell invasion of the underlying stroma. Tumour cells further traverse the endothelial basement membrane during entry into and egress from blood vessels3–5. Electron microscopic studies have shown local dissolution of basement membrane at its area of contact with invading tumour cells, suggesting an enzymatic mechanism3,6,7. Basement membranes are resilient structures which present a mechanical barrier to invasion8. Type IV collagen is a major structural protein of basement membranes and is chemically and genetically distinct from stroma collagen types I and III and cartilage collagen type II9,10. Previously characterised animal collagenases which cleave collagen types I; II and III fail to degrade type IV collagen11,12. We have recently purified about 1,000-fold and characterised a neutral protease activity preferential for type IV collagen from metastatic tumour cells and shown that it (1) produces specific degradation products, (2) has a molecular weight of 65,000, (3) is not plasmin or a cathepsin, by pH and inhibitor studies, and (4) does not significantly degrade other collagens or fibronectin12,13. Here we extend the relevance of this finding by quantitating the ability of several murine tumour cell lines of known metastatic potential to degrade type IV collagen. The cell lines with the highest incidence of spontaneous metastasis exhibit the greatest level of type IV collagen-degrading activity in two different assays using either living cells or media obtained from cell cultures.

Metastatic potential correlates with enzymatic degradation of basement membrane collagen.

Structure and biosynthesis of basement membranes.

Publisher Summary Basement membranes or basal laminae are ubiquitous in the vertebrate and invertebrate world and constitute important structural and functional extracellular matrices. Basement membranes are composed of fine fibrils, 40–60 A in diameter, arranged randomly in a granular matrix. Three general functions are ascribed to basement membranes: they (1) act as a semipermeable filter, (2) provide support, and (3) serve as a boundary between cell types or between cell layers and the underlying connective tissue. Basement membranes are insoluble in buffers at neutral pH, although small amounts of material can be brought into solution with acid buffers. Complete solubilization can be accomplished by reduction and alkylation in the presence of denaturant or after limited proteolysis. Collagen molecules are present in basement membranes. These apparently exist as triple-helical procollagen molecules composed of identical pro-α chains. Collagenous peptides equivalent in size to α chains can be isolated from digests of basement membranes. Noncollagenous glycoproteins are present in the matrix of most basement membranes; they are linked to the procollagen molecules via disulfide bonds and lysine- or hydroxylysine-derived cross-links.

Biochemistry and metabolism of basement membranes.

Proximal tubular epithelial cells from mice which develop autoimmune interstitial nephritis were found to express the nephritogenic target antigen, 3M-1. Anti-3M-1 mAbs (alpha 3M-1-Ab) were used to positively select for 3M-1-secreting tubular epithelium and, after stabilization in culture, this new cell line (MCT) was examined for the production of several moieties important to either immune interactions or to the development of extracellular matrix. Alkaline phosphatase-staining MCT cells also express epithelial growth factor receptors with a Kd of 0.87 nM and an epithelial growth factor receptor constant (Ro) of 2.1 X 10(4) receptors/cell. MCT culture supernatants contain greater amounts of laminin, and types IV and V procollagens compared to types I and III procollagens, and growing MCT cells on type I collagen matrix causes them to preferentially secrete even more type IV and V procollagen. The 30,000-Mr 3M-1 antigen could be immunoprecipitated from biosynthetically labeled MCT cell supernatants with alpha 3M-1-Ab. An identical-sized moiety was isolated by immunoaffinity chromatography from collagenase-solubilized mouse kidney tubular basement membranes. The 3M-1 antigen can be found on the MCT cell surface by radioimmunoassay, or deposited in a linear array in the extracellular matrix surrounding the MCT cells in culture by immunofluorescence. Mature messenger RNA species for both class I and class II major histocompatibility complex (MHC) molecules were detected by Northern hybridization, and their corresponding cell surface gene products were detected by cytofluorography of MCT cells stained with haplotype-specific antibodies. Both the cell surface 3M-1 and the small amounts of detected class II MHC molecules appear to be biologically functional, as MCT cells can support the proliferation of 3M-1-specific, class II MHC-restricted helper T cells in culture. These findings suggest that MCT cells provide all the necessary biological parameters for interfacing both as the target of a nephritogenic immune response, and as a potential source for new extracellular matrix which develops as a fibrogenic response to interstitial nephritis.

/pdf/characterization-of-a-renal-tubular-epithelial-cell-line-2kz53q88y2.pdf

Characterization of a renal tubular epithelial cell line which secretes the autologous target antigen of autoimmune experimental interstitial nephritis

Isolation of a collagen from basement membranes containing three identical α-chains

Endothelial injury is important in the pathogenesis of thrombosis, atherosclerosis, disseminated intravascular coagulation, and vasculitis. The ability of several common human viruses to infect cultures of endothelial cells obtained from human umbilical veins or bovine thoracic aorta was demonstrated. Indicators of infection included cytopathology, viral growth curves, and antigen detection by immunofluorescence. Herpes simplex virus type 1, adenovirus type 7, measles virus, and parainfluenza virus type 3 infected both human venous and bovine aorta endothelium. Mumps virus, poliovirus type 1, and echovirus type 9 grew only in human venous cells; coxsackievirus B4 infected only bovine arterial cultures; and cytomegalovirus, influenza A/Victoria/75 (H3N2) virus, and respiratory syncytial virus failed to grow in either cell culture. During replication some viruses caused acute lytic changes; some produced chronic, less destructive alterations; and other induced no apparent cytopathology. The results suggest that viral replication within endothelium may be important in the pathogenesis of viral disease of initiation of vessel-wall injury.

Nicholas A. Kefalides

Papers

Structure and biosynthesis of basement membranes.

Biochemistry and metabolism of basement membranes.

Characterization of a renal tubular epithelial cell line which secretes the autologous target antigen of autoimmune experimental interstitial nephritis

Isolation of a collagen from basement membranes containing three identical α-chains

Virus infection of endothelial cells.