Biochemistry: Protein Folding and Modifications

Changes made to a protein after its translation by ribosomes is complete. These modifications are catalyzed by enzymes and can include adding functional groups, proteolytic processing, and folding processes.

Examples include phosphorylation, neddylation, ubiquitination, proteolytic processing, and protein folding.

Proteins are made up of amino acids connected by peptide bonds, forming a polypeptide chain.

Peptide bonds are the links between amino acids in a protein.

The peptide bonds in proteins allow for rotation of the atoms, giving them flexibility.

Weak bonds that help proteins fold and maintain their shape. They include hydrogen bonds, electrostatic interactions, and van der Waals attractions.

The distribution of polar and nonpolar amino acids influences protein folding. Polar amino acids tend to be on the outside of the protein, while nonpolar amino acids tend to be on the inside.

Proper protein folding is crucial for their function. Misfolded proteins can be inactive or even harmful.

A covalent bond formed between two cysteine amino acid side chains.

The process of creating a disulfide bond between cysteine residues.

An oxidoreductase in bacteria that catalyzes disulfide bond formation in the periplasm.

An oxidoreductase in bacteria that reoxidizes DsbA, allowing it to continue catalyzing disulfide bond formation.

Sulfhydryl oxidoreductases in eukaryotes that catalyze disulfide bond formation in the endoplasmic reticulum.

FAD-dependent oxidases in yeast that reduce PDI, allowing it to continue catalyzing disulfide bond formation.

A specific sequence of amino acids within a protein that directs it to a particular cellular location.

Sorting motifs direct proteins to the correct cellular compartment, ensuring proper function and localization.

The movement of a protein across a biological membrane, from one cellular compartment to another.

A protein channel embedded in a membrane that facilitates the passage of proteins across the membrane.

A specific amino acid sequence that signals proteins to be transported into the nucleus.

A protein that binds to the NLS and guides proteins through the nuclear pore complex.

A small GTP-binding protein involved in nuclear transport, regulates the release of proteins at their destination.

An amino acid sequence that targets proteins for export out of the nucleus.

The removal of a portion of a polypeptide chain to activate a protein.

Acylation is the process of attaching a fatty acyl group (like myristoyl or palmitoyl) to a protein.

The process of adding or removing monosaccharides from a glycoprotein in the Golgi apparatus, usually involving various enzymes.

Acylation happens at the N-terminus (beginning) or C-terminus (end) of a protein.

A sugar molecule represented by a yellow hexagon, commonly found in glycoproteins.

A sugar molecule represented by a blue hexagon, often present in glycoproteins.

Prenylation adds an isoprenoid group (like farnesyl or geranylgeranyl) to a protein.

A sugar molecule represented by a red hexagon, sometimes part of glycoproteins.

Prenylation usually occurs at the C-terminus (end) of a protein.

A GPI anchor is a complex molecule composed of carbohydrates and lipids that attaches to a protein.

The addition of a phosphate group to a protein, often regulated by kinases, which can alter its function.

GPI anchors tether proteins to the cell membrane and direct them to the cell surface.

The attachment of an acetyl group to a protein, usually on side chains or the amino terminus.

The addition of a methyl group to a protein, often on specific side chains.

The main types of protein lipid modifications are acylation, prenylation, and GPI anchoring.

A protein domain that specifically recognizes and binds to phosphorylated tyrosine residues.

Protein lipid modifications affect where a protein is located inside the cell and its function.

A small protein that acts as a tag for proteins destined for degradation by the proteasome. It's attached to target proteins through a process called ubiquitination.

A large protein complex responsible for breaking down (degrading) proteins marked with ubiquitin tags. It's like a cellular recycling center.

The process of attaching ubiquitin molecules to a target protein. It involves a series of enzymatic steps including E1, E2, and E3 enzymes.

Enzymes involved in ubiquitination: E1 activates ubiquitin, E2 conjugates it to the target protein, and E3 facilitates the process.

A chain of multiple ubiquitin molecules linked together. The type of chain determines the fate of the target protein, such as degradation or other functions.

A common PTM where a phosphate group is added to a protein, often affecting its activity.

Both are PTMs, but ubiquitination tags proteins for degradation, while phosphorylation can modulate protein activity.