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Studies on the glycosylation of hydroxylysine residues during collagen biosynthesis and the subcellular localization of collagen galactosyltransferase and collagen glucosyltransferase in tendon and cartilage cells.

ABSTRACT: 1. The glycosylation of hydroxylysine during the biosynthesis of procollagen by embryonic chick tendon and cartilage cells was examined. When free and membrane-bound ribosomes isolated from cells labelled for 4min with [(14)C]lysine were assayed for hydroxy[(14)C]lysine and hydroxy[(14)C]lysine glycosides, it was found that hydroxylation took place only on membrane-bound ribosomes and that some synthesis of galactosylhydroxy[(14)C]lysine and glucosylgalactosylhydroxy[(14)C]lysine had occurred on the nascent peptides. 2. Assays of subcellular fractions isolated from tendon and cartilage cells labelled for 2h with [(14)C]lysine demonstrated that the glycosylation of procollagen polypeptides began in the rough endoplasmic reticulum. (14)C-labelled polypeptides present in the smooth endoplasmic reticulum and Golgi fractions were glycosylated to extents almost identical with the respective secreted procollagens. 3. Assays specific for collagen galactosyltransferase and collagen glucosyltransferase are described, using as substrate chemically treated bovine anterior-lens-capsule collagen. 4. When homogenates were assayed for the collagen glycosyltransferase activities, addition of Triton X-100 (0.01%, w/v) was found to stimulate enzyme activities by up to 45%, suggesting that the enzymes were probably membrane-bound. 5. Assays of subcellular fractions obtained by differential centrifugation for collagen galactosyltransferase activity indicated the specific activity to be highest in the microsomal fractions. Similar results were obtained for collagen glucosyltransferase activity. 6. When submicrosomal fractions obtained by discontinuous-sucrose-density-gradient-centrifugation procedures were assayed for these enzymic activities, the collagen galactosyltransferase was found to be distributed in the approximate ratio 7:3 between rough and smooth endoplasmic reticulum of both cell types. Similar determinations of collagen glucosyltransferase indicated a distribution in the approximate ratio 3:2 between rough and smooth microsomal fractions. 7. Assays of subcellular fractions for the plasma-membrane marker 5'-nucleotidase revealed a distribution markedly different from the distributions obtained for the collagen glycosyltransferase. 8. The studies described here demonstrate that glycosylation occurs early in the intracellular processing of procollagen polypeptides rather than at the plasma membrane, as was previously suggested.

SUBMITTER: Harwood R

PROVIDER: S-EPMC1172471 | biostudies-other | 1975 Nov

REPOSITORIES: biostudies-other

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Project description:1. The subcellular distribution of transglutaminase was investigated by using the analytical approach of differential and isopycnic centrifugation as applied to three organs of the rat: liver, kidney and lung. After differential centrifugation by the method of de Duve, Pressman, Gianetto, Wattiaux & Appelmans [(1955) Biochem. J. 63, 604-617], transglutaminase is mostly recovered in the unsedimentable fraction S and the nuclear fraction N. After isopycnic centrifugation of the N fraction in a sucrose density gradient, a high proportion of the enzyme remains at the top of the gradient; a second but minor peak of activity is present in high-density regions, where a small proportion of 5'-nucleotidase, a plasma-membrane marker, is present together with a large proportion of collagen recovered in that fraction. 2. Fractions where a peak of transglutaminase was apparent in the sucrose gradient were examined by electron microscopy. The main components are large membrane sheets with extracellular matrix and free collagen fibers. 3. As these results seem to indicate that some correlation exists between particulate transglutaminase distribution and those of collagen and plasma membranes, the possible binding of transglutaminase by collagen (type I) and by purified rat liver plasma membrane was investigated. 4. The binding studies indicated that collagen is able to bind transglutaminase and to make complexes with plasma-membrane fragments whose density is higher than that of plasma-membrane fragments alone. Transglutaminase cannot be removed from such complexes by 1% Triton X-100, but can be to a relatively large extent by 0.5 M-KCl and by 50% (w/v) glycerol. 5. Such results suggest that the apparent association of transglutaminase with plasma membrane originates from binding in vitro of the cytosolic enzyme to plasma membrane bound to collagen, which takes place during homogenization of the tissue, when the soluble enzyme and extracellular components are brought together.

Project description:Urimary excretion of hydroxyprolin (Hyp) is one index of total collagen degradation, from all sources. Since some of the Hyp released from collagen may be further metabolized before it is excreted, other markers are necessary to measure collagen breakdown. Excretion of the glycosides of hydroxylysine (Hyl), glucosyl galactosyl hydroxylysine (Hy1[Gl)cGa1]), and galactosyl hydroxylysine (Hyl[Ga)]), more accurately reflects collagen metabolism since these products occur in specificratios in different tissue collagens and are themselves metabolized only to a minor degree. The ratios of total Hy1/Hyp and Hyl(GlcGal)/Hyl(Ga1) were measured in the urine of norma. subjects and of patients with Paget's disease of bone, hyperphosphatasia, and extensive thermal burns. In patients with extensive thermal burns the pattern of urinary Hy1 and its glycosides was consistent with degradation of collagen in dermis and fascia. When bone collagen degradation was dominant, the pattern of urinary metabolites reflected that source. Pagetic bone collagen has an amino acid composition similar to normal bone and Hy1(G1cGa1/Hyl(G1) of 0.396-0.743,vs. normal of 0.474+/-0.088. In untreated patients with severe Paget's disease of bone or hyperphosphatasia (urinary Hyp greater than 2.0 micronmol/mg creatinine) urinary Hyl/Hyp averaged 0.052+/-0.042 (0.042+/-0.009 in normal bone) and Hy1(G1cGa1)/Hy1(Ga1) 0.601+/-0.017 (0.47+/-0.009 in normal bone). When bone resorption was decreased sufficiently with calcitonin or disodium etidronate in these patients, both the urinary ratios of Hy1/Hyp and Hy1(G1cGa1)/Hyl(Gal) rose. In normal subjects treated with calcitonin and excreting relatively little Hyp, the ratio of Hy1/H)P approached 0.7 and Hy1(G1ycGa1)/Hy1(Ga1) approached 3.5. There increased ratios reveal the existence of a source of collagen breakdown other than skin or bone. The first subcompoent of complement, Clq, which has collagen-like sequences, relatively high amounts of Hy1, and most of the glycosylated Hy1 as Hy1(G1cGa1), could be the source of these metabolites.

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Studies on the glycosylation of hydroxylysine residues during collagen biosynthesis and the subcellular localization of collagen galactosyltransferase and collagen glucosyltransferase in tendon and cartilage cells.

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