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Related Concept Videos

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.
A protein's shape is critical to its function. For example, an enzyme can...
Amyloid Fibrils03:03

Amyloid Fibrils

Amyloid fibrils are aggregates of misfolded proteins.  Under most circumstances, misfolded proteins are either refolded by chaperone proteins or degraded by the proteasome. However, in the case of a mutation or a disease, these proteins can accumulate to form large clusters and often further assemble to form elongated fibers, called fibrils. 
Amyloid deposits were observed as early as 1639 in the liver and the spleen.   In 1854, Rudolph Virchow performed iodine staining, normally used to...
Formation of Higher-order Actin Filaments01:11

Formation of Higher-order Actin Filaments

The polymerization of G-actin monomers into filamentous F-actin is a multi-step process. Once the F-actins are formed, they can bundle together in different arrangements to form higher-order networks and regulate cellular functions. Common examples include the formation of lamellipodia and filopodia at the cell's leading edge by actin reorganization in a migrating cell. The microvilli on the brush border epithelial cells are also formed through the F-actin network.
The high-order actin networks...
Generation of Straight or Branched Actin Filaments01:14

Generation of Straight or Branched Actin Filaments

The straight or branched structure formation of actin filaments is controlled by nucleating proteins such as the formins and Arp2/3 complex. Formin-mediated assembly results in straight filaments, whereas Arp2/3 protein complex-mediated assembly results in branched actin filaments.
Arp2/3 Complex
Arp2/3 complex is a seven-subunit complex consisting of two proteins similar to actin- Arp2 and Arp3, and five other subunits that help keep Arp2 and Arp3 inactive. When required, the complex is...
Globular and Fibrous Proteins02:21

Globular and Fibrous Proteins

Many proteins can be classified into two distinct subtypes - globular or fibrous. These two types differ in their shapes and solubilities.
Globular proteins are also known as spheroproteins and typically are approximately round in shape. They contain a mix of amino acid types and contain differing sequences in their primary structures. Globular proteins have many different functions, such as enzymes, cellular messengers, and molecular transporters. These roles often require the proteins to be...
Globular and Fibrous Proteins02:21

Globular and Fibrous Proteins

Many proteins can be classified into two distinct subtypes - globular or fibrous. These two types differ in their shapes and solubilities.
Globular proteins are also known as spheroproteins and typically are approximately round in shape. They contain a mix of amino acid types and contain differing sequences in their primary structures. Globular proteins have many different functions, such as enzymes, cellular messengers, and molecular transporters. These roles often require the proteins to be...

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Related Experiment Video

Updated: Jun 16, 2026

Determination of Glucan Chain Length Distribution of Glycogen Using the Fluorophore-Assisted Carbohydrate Electrophoresis (FACE) Method
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Determination of Glucan Chain Length Distribution of Glycogen Using the Fluorophore-Assisted Carbohydrate Electrophoresis (FACE) Method

Published on: March 31, 2022

Glucagon fibril polymorphism reflects differences in protofilament backbone structure.

Christian Beyschau Andersen1, Matthew R Hicks, Valeria Vetri

  • 1Protein Structure and Biophysics, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Måløv, Denmark.

Journal of Molecular Biology
|February 17, 2010
PubMed
Summary

Glucagon peptide hormone forms two distinct amyloid fibril structures, twisted and straight, with differing morphologies and structural properties. These structural variations, including secondary structure and backbone stability, are inherent to the glucagon sequence itself.

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Experimental Approaches for Biochemical Analysis of Glial Fibrillary Acidic Protein and Its Disease-associated Variants
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Experimental Approaches for Biochemical Analysis of Glial Fibrillary Acidic Protein and Its Disease-associated Variants

Published on: November 28, 2025

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Last Updated: Jun 16, 2026

Determination of Glucan Chain Length Distribution of Glycogen Using the Fluorophore-Assisted Carbohydrate Electrophoresis (FACE) Method
06:13

Determination of Glucan Chain Length Distribution of Glycogen Using the Fluorophore-Assisted Carbohydrate Electrophoresis (FACE) Method

Published on: March 31, 2022

Experimental Approaches for Biochemical Analysis of Glial Fibrillary Acidic Protein and Its Disease-associated Variants
06:02

Experimental Approaches for Biochemical Analysis of Glial Fibrillary Acidic Protein and Its Disease-associated Variants

Published on: November 28, 2025

Area of Science:

  • Biochemistry
  • Structural Biology
  • Biophysics

Background:

  • Amyloid fibrils are associated with various diseases.
  • The peptide hormone glucagon can form amyloid fibrils.
  • Glucagon exhibits polymorphism, forming distinct fibril structures.

Purpose of the Study:

  • To investigate the structural differences between glucagon amyloid fibrils formed at low and high concentrations.
  • To elucidate the molecular basis of glucagon polymorphism.

Main Methods:

  • Transmission electron microscopy (TEM) for morphology.
  • Proteolytic degradation for stability and accessibility.
  • Circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) for secondary structure.
  • Linear dichroism (LD) for chromophore alignment.
  • X-ray fiber diffraction for fibril superstructure.

Main Results:

  • Low-concentration glucagon fibrils are twisted, composed of multiple protofilaments.
  • High-concentration glucagon fibrils are straight, composed of two protofilaments.
  • Twisted fibrils exhibit beta-turn rich CD spectra and weaker hydrogen bonding.
  • Straight fibrils show beta-sheet rich CD spectra, higher order, and greater stability.
  • Structural differences are observed at all levels, from backbone to superstructure.

Conclusions:

  • Glucagon polymorphism results in distinct fibril structures with differing secondary structures and stability.
  • The observed morphological and structural differences are intrinsic to the glucagon sequence.
  • Glucagon serves as a model for understanding how a single peptide sequence can adopt diverse fibrillar forms.