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Protein and Protein Structure02:15

Protein and Protein Structure

Proteins are one of the most abundant organic molecules in living systems and have the most diverse range of functions of all macromolecules. Proteins may be structural, regulatory, contractile, or protective. They may serve in transport, storage, or membranes; or they may be toxins or enzymes. Their structures, like their functions, vary greatly. They are all, however, amino acid polymers arranged in a linear sequence.
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Insulin secretory vesicles release insulin to stimulate blood glucose uptake and regulate carbohydrate metabolism. When the blood glucose levels increase, glucose enters the pancreatic β-islet cells through glucose transporters. Once inside, glucose is metabolized through glycolysis, the citric acid cycle, and the electron transport chain, producing ATP. This increase in ATP concentration closes ATP-sensitive potassium channels, leading to depolarization of the membrane and the opening of...
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The pancreatic islets comprising only 1%-2% of the volume are highly vascularized and innervated mini-organs. They contain five endocrine cell types, including β cells that secrete insulin, which is synthesized as a single polypeptide chain, preproinsulin, processed to proinsulin, and finally to insulin and C-peptide. This process is complex and regulated, involving the Golgi complex, the endoplasmic reticulum, and the secretory granules of the β cell.
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Insulin action is mediated through a receptor tyrosine kinase, akin to the IGF-1 receptor. The number of receptors per cell varies significantly, from 40 on erythrocytes to 300,000 on adipocytes and hepatocytes. The insulin receptor consists of linked α/β subunit dimers, forming a heterotetramer glycoprotein with two extracellular α subunits and two β subunits spanning the membrane. The α subunits inhibit the inherent tyrosine kinase activity of the β subunits, but this inhibition is released...
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The endoplasmic reticulum (ER) of pancreatic β-cells synthesizes preproinsulin, which consists of a signal peptide, A and B chains, and a C-peptide. Preproinsulin is then cleaved and folded into proinsulin, which translocates to the Golgi apparatus for sorting and packaging into secretory granules. In these granules, enzymatic clipping generates insulin and C-peptide.
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Related Experiment Video

Updated: Jul 23, 2026

A Method for Mouse Pancreatic Islet Isolation and Intracellular cAMP Determination
12:33

A Method for Mouse Pancreatic Islet Isolation and Intracellular cAMP Determination

Published on: June 25, 2014

Separate functional features of proinsulin C-peptide.

M Henriksson1, E Nordling, E Melles

  • 1Department of Medical Biochemistry and Biophysics, Karolinska Institutet, 171 77, Stockholm, Sweden.

Cellular and Molecular Life Sciences : CMLS
|July 9, 2005
PubMed
Summary

Proinsulin C-peptide

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Area of Science:

  • Biochemistry and Molecular Biology
  • Endocrinology
  • Cellular Signaling

Background:

  • Proinsulin C-peptide has physiological roles beyond its function in insulin production.
  • C-peptide is a potential therapeutic for type 1 diabetes, but its mechanisms are not fully understood.
  • Identifying C-peptide's functional interactions is crucial for therapeutic development.

Purpose of the Study:

  • To investigate the functional effects of proinsulin C-peptide variants.
  • To identify key residues and structural features of C-peptide that influence cellular activity.
  • To correlate C-peptide structure with its ability to modulate mitogen-activated protein kinase (MAPK) phosphorylation.

Main Methods:

  • Comparative analysis of 22 mammalian proinsulin C-peptide sequences.
  • Design and synthesis of C-peptide analogues for activity studies.
  • Functional assays measuring MAPK phosphorylation in Swiss 3T3 fibroblasts.

Main Results:

  • Conserved glutamic acid residues at positions 3, 11, and 27 of C-peptide promote MAPK phosphorylation.
  • Helix-promoting residues in the N-terminal segment enhance C-peptide's functional activity.
  • Findings indicate that both N-terminal and C-terminal segments of C-peptide contribute to its complex interactions.

Conclusions:

  • Specific residues and structural elements within C-peptide are critical for its functional effects on MAPK signaling.
  • C-peptide's biological activity is mediated by complex and potentially multiple interaction sites.
  • These findings advance the understanding of C-peptide's role in cellular processes and its therapeutic potential.