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Collagen biosynthesis. Characterization of subcellular fractions from embyonic chick fibroblasts and the intracellular localization of protocollagen prolyl and protocollagen lysyl hydroxylases.

ABSTRACT: 1. Subcellular fractions of freshly isolated matrix-free embryonic chick tendon and sternal cartilage cells have been characterized by chemical analysis, electron microscopy and the location of specific marker enzymes. These data indicate the fractions to be of a high degree of purity comparable with those obtained from other tissues, e.g. liver and kidney. 2. When homogenates were assayed for protocollagen prolyl hydroxylase and protocollagen lysyl hydroxylase activities, addition of Triton X-100 (0.1%, w/v) was found to stimulate enzyme activities by up to 60% suggesting that the enzymes were probably membrane-bound. 3. Assay of subcellular fractions obtained by differential centrifugation for protocollagen prolyl hydroxylase activity indicated the specific activity to be highest in the microsomal fraction. Similar results were obtained for protocollagen lysyl hydroxylase activity. 4. Submicrosomal fractions obtained by discontinuous sucrose-gradient centrifugation were assayed for the two enzymes and protocollagen prolyl hydroxylase and protocollagen lysyl hydroxylase were found to be associated almost exclusively with the rough endoplasmic reticulum fraction in both tendon and cartilage cells.

SUBMITTER: Harwood R

PROVIDER: S-EPMC1168472 | biostudies-other | 1974 Oct

REPOSITORIES: biostudies-other

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Project description:The hydroxylation of proline residues to 4-trans-hydroxyproline (Hyp) is a common post-translational protein modification in plants, mediated by prolyl 4-hydroxylases (P4Hs). Hyps predominantly occur in a group of cell wall proteins, the Hydroxyproline-rich glycoproteins (HRGPs), where they are frequently O-glycosylated. While prolyl-hydroxylation and O-glycosylation are important, e.g. for cell wall stability, they are not desirable in plant-made pharmaceuticals. Sequence motifs recognized for prolyl-hydroxylation derived from vascular plants were proposed but did not include data from mosses, such as Physcomitrella. Here, a phylogenetic reconstruction of plant P4Hs identified six P4Hs in four subfamilies in mosses. We analysed the amino acid sequences and structural environments around Hyps in Physcomitrella utilizing 73 Hyp sites in 24 secretory proteins from multiple MS/MS datasets, and found that prolines in close proximity to other prolines, alanine, serine, threonine and valine were preferentially hydroxylated. About 95 % of the Hyp sites were predictable with a combination of previously defined motifs and methods. In our data, AOV (Ala-Hyp-Val) was the most frequent prolyl-hydroxylation pattern. Additionally, short arabinose chains were attached to Hyps in two cell-wall pectinesterases. A combination of 443 AlphaFold structure models and our MS data of peptides with nearly 3000 proline sites found Hyps predominantly on protein surfaces in disordered regions. Moss-produced human erythropoietin (EPO) exhibited plant-specific O-glycosylation with arabinose chains on two Hyps. This modification was significantly reduced in a P4H1 single knock-out (KO) Physcomitrella mutant. Quantitative proteomics after isotope labelling with different P4H-KO moss mutants revealed specific changes in the amount of proteins, including HRGPs, and a modified prolyl-hydroxylation pattern from the mutants, suggesting a differential function of the six Physcomitrella P4Hs. Quantitative RT-PCR proved a differential effect of single P4H KOs on the expression of the other five p4h genes, suggesting a partial compensation of the mutation. AlphaFold-Multimer models for Physcomitrella P4H1 and its target EPO peptide superposed with the crystal structure of Chlamydomonas P4H1 and a peptide substrate suggested significant amino acids in the active centre of the enzyme that form H-bonds with the peptide substrate, and revealed differences between P4H1 and the other five Physcomitrella P4Hs.

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Collagen biosynthesis. Characterization of subcellular fractions from embyonic chick fibroblasts and the intracellular localization of protocollagen prolyl and protocollagen lysyl hydroxylases.

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