Identification of extractable proteins from the bovine ocular zonule: Major zonular antigens of 32kD and 250kD

Abstract

Using Western immunoblotting, the extractable proteins of the bovine zonular fibers were examined for reactivity with two zonular antisera known to have strong affinity for zonular fibers in tissues, in order to identify the antigenic components. The extracts were also tested with antisera to several matrix proteins that have been reported to be associated with zonular fibers. Proteins reactive with antisera to bovine serum albumin, serum immunoglobulins and fibronectin were present. No bands reactive with antisera to a-elastin, prealbumin, amyloid P component, collagen VI, lysyl oxidase or monoclonal antibody to fibrillin were demonstrated. The major nonserum protein band identified by both antisera was a 32kD polypeptide. An equally strong 250kD polypeptide was shown by the antiserum to guanidine-dithiothreitol extracted zonular fibers. Both of these proteins were PAS-positive and were demonstrated also by the antisera in extracts of bovine elastic neck ligament. Whether the two glycoproteins are related to each other, with the higher molecular weight protein either a precursor or aggregate form, is not yet clear. They appear to bear a close relationship to the elusive core microfibrillar protein.

Association of fibronectin with the microfibrils of connective tissue

“…Several glycoproteins have been described in microfibrils (Sear et al, 1978;Cleary and Gibson, 1983;Jaques and Serafini-Fracassini, 1986;Gibson et al, 1986); the main ones seem to be those described as 31 KDa (MAGP) by Gibson et al (1986) and 32 KDa by Streeten and Gibson (1988). However, these substances have not been related so far to any of the structures described in microfibrils.…”

“…Bar = 100 pm; X 225. 3, A third glycoprotein, fibronectin, has been identified by Krauhs (1983)) Schwartz et al (1985), Goldfischer et al (1985), and Streeten and Gibson (1988). The localization of fibronectin on microfibrils is not known, but it has been suggested by Schwartz et al (1985) that it is present at the surface rather than within the core of microfibrils.…”

“…The amyloid P component (amyloid P), a glycoprotein present in amyloid deposits as well as in serum, has been detected by immunostaining along the surface of elastic fibers (Breathnach et al, 1981) and attributed to microfibrils. While amyloid P antigenicity has not been found in extracts of cattle ligamentum nuchae (Gibson et al, 1986) and zonular fibers (Streeten and Gibson, 1988), it could have been lost during the extraction procedure. In the mouse, the microfibrils of zonular fibers and foot pad connective tissue are immunostained by anti-amyloid P antiserum followed by either the PAP technique or protein Agold, whereas the antiserum adsorbed with amyloid P has yielded no reaction with either technique .…”

The Extracellular Matrix Protein MAGP-2 Interacts with Jagged1 and Induces Its Shedding from the Cell Surface

“…Microfibrils are located at the periphery of elastin in elastic fibers (9,10) and during development microfibril components are usually expressed just prior to elastin, suggesting that they orchestrate the deposition of elastin into the fiber (11,12). Microfibrils may serve other functions as well, such as augmenting the mechanical properties of elastin (13,14), providing anchorage in nonelastic tissues such as the ocular zonules (15), mediating attachment of epithelium and endothelium to the elastic matrix (16,17), and anchoring platelet adhesion (18).…”