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Related Concept Videos

Osteoclasts in Bone Remodeling01:31

Osteoclasts in Bone Remodeling

Osteoclasts are cells responsible for bone resorption and remodeling. They originate from hematopoietic progenitor cells present in the bone marrow. Numerous progenitor cells fuse to form multinucleated cells, each with 10-20 nuclei. A single osteoclast has a diameter of 150 to 200 µM. These cells have ruffled borders that break down the underlying bone tissue and release minerals such as calcium into the blood in bone resorption. Osteoclasts cling to bones with their ruffled edges during bone...
Covalently Linked Protein Regulators02:04

Covalently Linked Protein Regulators

Proteins can undergo many types of post-translational modifications, often in response to changes in their environment. These modifications play an important role in the function and stability of these proteins. Covalently linked molecules include functional groups, such as methyl, acetyl, and phosphate groups, and also small proteins, such as ubiquitin. There are around 200 different types of covalent regulators that have been identified.
These groups modify specific amino acids in a protein.
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Related Experiment Videos

Post-translational modification and proteolytic processing of urinary osteopontin.

Brian Christensen1, Torben E Petersen, Esben S Sørensen

  • 1Protein Chemistry Laboratory, Department of Molecular Biology and Interdisciplinary Nanoscience Center (iNANO), University of Aarhus, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark.

The Biochemical Journal
|December 13, 2007
PubMed
Summary

Osteopontin (OPN) in urine may prevent kidney stones by inhibiting crystal formation. This study characterized OPN's post-translational modifications, revealing its complex role in mineralization and stone disease.

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Area of Science:

  • Biochemistry
  • Nephrology
  • Proteomics

Background:

  • Osteopontin (OPN) is a glycoprotein found in various tissues and bodily fluids.
  • In urine, OPN inhibits calcium oxalate crystal formation, suggesting a role in preventing kidney stones.
  • However, OPN's role in nephrolithiasis is complex, as it's also found in renal calculi.

Purpose of the Study:

  • To characterize the post-translational modifications (PTMs) of intact human urinary OPN and its N-terminal fragments.
  • To elucidate the specific PTMs that influence OPN's function in the urinary system.
  • To understand the structural basis of OPN's involvement in kidney stone formation or prevention.

Main Methods:

  • Mass spectrometry (MS) analysis of intact urinary OPN.
  • Enzymatic dephosphorylation and peptide mass analyses.
  • Peptide mapping and immunoblotting with monoclonal antibodies.

Main Results:

  • Intact urinary OPN has a mass of 37.7 kDa.
  • OPN contains approximately eight phosphate groups on 30 potential sites, one sulfated tyrosine, and five O-linked glycosylations.
  • No N-linked glycans were detected; N-terminal fragments result from cleavage at specific sites.

Conclusions:

  • Urinary OPN undergoes extensive PTMs, including phosphorylation, sulfation, and glycosylation.
  • These modifications likely regulate OPN's function in mineralization and its role in kidney stone disease.
  • Understanding OPN's PTMs is crucial for deciphering its dual role in renal stone formation and prevention.