amyloid-beta peptide

Examples of amyloid-beta peptide in the following topics:

• Alzheimer's Disease

  • In 1991, the amyloid hypothesis postulated that amyloid beta (Aβ) deposits are the fundamental cause of the disease.
  • In 2009, this theory was updated, suggesting that a close relative of the beta-amyloid protein, and not necessarily the beta-amyloid itself, may be a major culprit in the disease.
  • N-APP, a fragment of APP from the peptide's N-terminus, is adjacent to beta-amyloid and is cleaved from APP by one of the same enzymes.
  • In this model, beta-amyloid plays a complementary role, by depressing synaptic function.
  • Enzymes act on the APP (Amyloid precursor protein) and cut it into fragments of protein, one of which is called beta-amyloid and its crucial in the formation of senile plaques in AD

• T Cell Receptors

  • MHC molecules and peptides form complexes on the surface of antigen presenting cells (APCs).
  • The receptor that recognizes these peptide-MHC complexes is called the T Cell Receptor (TCR).
  • Each alpha and beta chain consists of one variable domain (V), one constant domain (C), a hydrophobic transmembrane region, and a short cytoplasmic region .
  • The recognition of peptide-MHC complexes is mediated by CDRs formed by both the alpha and beta chains of the TCR.
  • T cell receptor consists of alpha and beta chains, a transmembrane domain, and a cytoplasmic region.

• Secondary & Tertiary Structure of Large Peptides and Proteins

  • Bulky side-chain substituents destabilize this arrangement due to steric crowding, so this beta-sheet conformation is usually limited to peptides having a large amount of glycine and alanine.
  • Although most proteins and large peptides may have alpha-helix and beta-sheet segments, their tertiary structures may consist of less highly organized turns, strands and coils.
  • A large section of antiparallel beta-sheets is colored violet, and a short alpha-helix is green.
  • The remaining peptide chain seems disorganized, but certain features such as a 180º turn (called a beta-turn) and five disulfide bonds can be identified.
  • The hemoglobin molecule is an assembly of four protein subunits, two alpha units and two beta units.

• Prions

  • All known prions induce the formation of an amyloid fold, in which the protein polymerises into an aggregate consisting of tightly-packed beta sheets.
  • Amyloid aggregates are fibrils, growing at their ends, and replicating when breakage causes two growing ends to become four growing ends.
  • This problem does not arise if PrPSc exists only in aggregated forms such as amyloid, where cooperativity may act as a barrier to spontaneous conversion.

• Insulin Secretion and Regulation of Glucagon

  • Glucagon is a peptide hormone that works in conjunction with insulin to maintain a stable blood glucose level.
  • Glucagon and insulin are peptide hormones secreted by the pancreas that play a key role in maintaining a stable blood glucose level.
  • Insulin is produced by beta cells in the pancreas and acts to oppose the functions of glucagon.

• The Incorporation of Nonstandard Amino Acids

  • Also, enzymes may remove amino acids from the amino end of the protein, or cut the peptide chain in the middle.
  • For instance, the peptide hormone insulin is cut twice after disulfide bonds are formed, and a propeptide is removed from the middle of the chain; the resulting protein consists of two polypeptide chains connected by disulfide bonds.
  • It is important to compare the structures of alanine and beta alanine.
  • In alanine, the side-chain is a methyl group; in beta alanine, the side-chain contains a methylene group connected to an amino group, and the alpha carbon lacks an amino group.
  • A rare exception to the dominance of α-amino acids in biology is the β-amino acid beta alanine (3-aminopropanoic acid), which is used in plants and microorganisms in the synthesis of pantothenic acid (vitamin B5), a component of coenzyme A.

• Inhibiting Cell Wall Synthesis

  • β-Lactam (beta-lactam) and glycopeptide antibiotics work by inhibiting or interfering with cell wall synthesis of the target bacteria.
  • The first class of antimicrobial drugs that interfere with cell wall synthesis are the β-Lactam antibiotics (beta-lactam antibiotics), consisting of all antibiotic agents that contains a β-lactam nucleus in their molecular structures.
  • The second class of antimicrobial drugs that interfere with cell wall synthesis are the glycopeptide antibiotics, which are composed of glycosylated cyclic or polycyclic nonribosomal peptides.
  • Describe the two types of antimicrobial drugs that inhibit cell wall synthesis: beta-lactam and glycopeptide antibiotics

• Digestive Processes of the Small Intestine

  • Proteins are degraded into small peptides and amino acids before absorption.
  • Proteolytic enzymes, including trypsin and chymotrypsin, are secreted by the pancreas and cleave proteins into smaller peptides.
  • This is because the cellulose is made out of beta-glucose that makes the inter-monosaccharidal bindings different from the ones present in starch, which consists of alpha-glucose.
  • Humans lack the enzyme for splitting the beta-glucose-bonds—that is reserved for herbivores and bacteria in the large intestine.

• Interactions of Hormones at Target Cells

  • Bundles of cells in the pancreas, called the islets of Langerhans, contain two kinds of cells: alpha cells and beta cells.
  • Beta cells secrete insulin.
  • When the concentration of blood glucose rises, such as after eating, beta cells secrete insulin into the blood.
  • Glucagon is a pancreatic peptide hormone that, as a counter-regulatory hormone for insulin, stimulates glucose release by the liver and maintains glucose homeostasis.

• Cerebrospinal Fluid and Its Circulation

  • The three biomarkers are CSF amyloid beta 1-42, total CSF tau protein, and P-Tau181P.