The Biochemistry of Bovine Spongiform Encephalopathy

The Biochemistry of Bovine Spongiform Encephalopathy (BSE)

Otherwise Known as Mad Cow Disease

Model of an Essential Amino Acid

The sulfur group thiol is prone to oxidation.

Hydrophobic.

(Arizona)

Two Chemical Characteristics of Methionine

Levels of Protein Structure

Dehydration Synthesis and the Formation of a Peptide Bond

Two amino acids are joined together by a peptide bond.

During this process the glycine loses an OH from its carboxyl group and Alanine loses it H from its amine group forming water or H2O.

Hydrolysis and the Breaking of the Peptide Bond

The peptide bond is broken when water or H2O is added to a polypeptide.

The OH will go to the carboxyl group of the Glycine and the H will go to the amine group of the alanine to complete the two amino acids.

Hydrophobic Interactions

Hydrogen Bonds

Ionic Bonding

Disulfide Bridges

Four Forces that stabilize a Proteins Three-Dimensional Structure

Hydrophobic Interactions are the clustering of hydrophobic R groups in the center of the molecule to minimize contact with water.

Hydrophobic Interactions

A hydrogen bond forms when two atoms are electrostatically attracted to each other between molecules.

When the two molecules are in side amino acid chains, the tertiary structure is stabilized.

Amino acids with oxygen or nitrogen will form these hydrogen bonds.

Hydrogen Bonds

An electrostatic attraction between two polar side amino acid chains help stabilize the structure at the core of the protein.

Ionic Bonding

A strong force created when two cysteine side groups form a covalent bond.

Disulfide Bridges

Prions are proteins that occur naturally in a cell membrane and are designated PrPc.

Infected prions are designated PrPsc and have the same amino acid sequence as PrPc, but are shaped differently.

The PrPscs enter through infected feed that is made from other animals.

The PrPscs will convert PrPcs into PrPscs.

(Hudon-Miller)

The Role of Prions in BSE

Misfolding causes a changes in the protein, making it hydrophobic and unable to function normally.

The infected protein (PrPsc) acts as a chaperone and infects other PrPcs.

The infected PrPcs cannot do their job in the cell so the cell produces more PrPcs to do the job.

As more are produced, more get infected.

(Hudon-Miller)

Protein Misfolding and Aggregation in BSE

The infected PrPc are not recognized by the Proteasomes and are not eliminated by the cell.

The infected PrPcs build up and begin to aggregate or stick together.

This aggregation and build up of infected PrPcs eventually leads to cell death.

As cells die within tissue, the place of the cell is not filled creating sponge like holes.

(Hudon-Miller)

Protein Misfolding and Aggregation in BSE

The role of a normal chaperone is to enable proteins to fold normally.

PrPscs will act as a chaperone to cause the misfolding in PrPcs allowing them to become PrPscs.

Normal chaperones have no effect on the PrPscs so they cannot fix or transform the PrPscs back to PrPcs.

(Hudon-Miller)

Role of the Chaperone Protein

Prohibit the inclusion of brain and spinal cord tissue in feed.

Removal of brain and spinal cord tissue at slaughter and processing.

Surveillance of occurrences of neurological disorders.

Awareness programs to aid surveillance.

Screening tests at slaughter.

Destruction of animals exposed to contaminated feed.

Appropriate disposal of carcasses and animal byproducts.

(OIE)

How Can the USA Decrease the Risk of BSE in the Food Supply

Clark, J (2012) The Structure of Proteins. Chemguide. March 27, 2014 from http://www.chemguide.co.uk/organicprops/aminoacids/proteinstruct.html

OIE, (2014) Prevention and Control. OIE, World Organisation for Animal Health. March 28, 2014 from http://www.oie.int/animal-health-in-the-world/bse-portal/prevention-and-control/

Arizona (2003) Methionine. The Biology Project. March 23, 2014 from http://www.biology.arizona.edu/biochemistry/problem_sets/aa/Methionine.html

Hudon-Miller, S. (2012) Bovine spongiform encephalopathy. March 27, 2014 from http://youtu.be/TE8e5rRreSE

References