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Related Concept Videos

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...
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...
Protein Folding01:25

Protein Folding

Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to its biological function. Interactions between its constituent amino acids guide protein folding, and hence the protein structure is primarily dependent on its amino acid sequence.
Protein Structure Is Critical to Its Biological Function
Proteins perform a wide range of biological functions such as catalyzing chemical reactions, providing...
Protein Folding01:22

Protein Folding

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Protein Folding Quality Check in the RER01:29

Protein Folding Quality Check in the RER

ER is the primary site for the maturation and folding of soluble and transmembrane secretory proteins. The calnexin cycle is a specific chaperone system that folds and assesses the confirmation of N-glycosylated proteins before they can exit the ER lumen. The primary players of this quality check pipeline are the lectins, ER-resident chaperones, and a glucosyl transferase enzyme. In case the calnexin system in the lumen fails to salvage a misfolded protein, it is transported to the cytoplasm...

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Competition between folding, native-state dimerisation and amyloid aggregation in beta-lactoglobulin.

Daizo Hamada1, Toshiki Tanaka, Gian Gaetano Tartaglia

  • 1Department of Developmental Infectious Diseases, Osaka Medical Center for Maternal and Child Health, 840 Murodo, Izumi, Osaka 594-1101, Japan. daizo@med.kobe-u.ac.jp

Journal of Molecular Biology
|January 10, 2009
PubMed
Summary

Individual beta-strands of beta-lactoglobulin can form amyloid aggregates. These aggregates can seed fibril formation in reduced, but not intact, full-length beta-lactoglobulin, highlighting the role of unfolding in aggregation.

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Area of Science:

  • Biochemistry
  • Protein Misfolding Diseases
  • Structural Biology

Background:

  • Beta-lactoglobulin is a major whey protein.
  • Protein misfolding and amyloid aggregation are implicated in various diseases.
  • Understanding the intrinsic aggregation propensity of protein segments is crucial.

Purpose of the Study:

  • To investigate the amyloid aggregation propensity of individual beta-strands from beta-lactoglobulin.
  • To determine if these peptide aggregates can seed fibril formation in full-length beta-lactoglobulin under different conditions.
  • To explore the role of disulfide bonds and sequence context in modulating aggregation.

Main Methods:

  • Synthesis of peptides corresponding to individual beta-strands of beta-lactoglobulin.
  • Amyloid aggregate formation assays using these peptides.
  • Seeding experiments with full-length beta-lactoglobulin (reduced and intact disulfide bonds).
  • Analysis of the effect of specific beta-strands (e.g., betaA, betaI) on aggregation.

Main Results:

  • Individual beta-strands readily form amyloid aggregates.
  • Peptide aggregates can seed fibril formation in reduced full-length beta-lactoglobulin.
  • Preformed fibrils of betaA promote aggregation in intact full-length beta-lactoglobulin.
  • High intrinsic aggregation propensity regions require partial unfolding to aggregate.
  • The betaI strand's aggregation propensity favors dimerization due to disulfide stabilization, not misfolding.

Conclusions:

  • Intrinsic amyloidogenicity of protein segments can be masked by native-state stabilizing interactions.
  • Partial unfolding is necessary for aggregation of intrinsically aggregation-prone regions.
  • The overall protein sequence can act as a 'negative design' to prevent aggregation, likely shaped by evolution.
  • Disulfide bonds and native structure play critical roles in preventing misfolding and aggregation.