Protein Sorting and Vesicular Transport Flashcards

This set covers protein translocation into the ER, vesicle budding and fusion mechanisms, and protein modification and quality control within the endomembrane system.

N-terminal signal sequence

A sequence on proteins destined for the endoplasmic reticulum that leads to the docking of the ribosome and entry of the protein across the ER membrane during synthesis.

Rough endoplasmic reticulum (RER)

A region of the ER consisting of membranes and polyribosomes that are in the process of translating and translocating proteins into the ER membrane and lumen.

Cytosol

The cellular location where ribosomes translate mRNAs that encode cytoplasmic proteins, such as ribosomal proteins.

Signal-recognition particle (SRP)

A cytosolic component that binds to the N-terminal signal sequence of a protein and carries the ribosome to the ER membrane.

Stop-transfer sequence

An internal hydrophobic sequence that causes the translocation channel to discharge a protein sideways into the lipid bilayer, making it a transmembrane protein.

Secretory (exocytic) pathway

The pathway through which proteins are transported out of a cell, passing through the endoplasmic reticulum and the Golgi apparatus.

Endocytic pathway

The pathway through which fluids and macromolecules are transported into the cell.

Endomembrane system

A system of organelles, including the ER and Golgi, that are linked by transport vesicles.

Disulfide bonds

Covalent bonds formed by the oxidation of cysteine side chains in the ER lumen that stabilize protein structure; they do not form in the reducing environment of the cytosol.

Clathrin

Molecules that act at the cytosolic surface of membranes to help shape vesicles, which are released once budding occurs.

Adaptins

Proteins that select cargo for transport by capturing cargo receptors and interacting with clathrin during vesicle budding.

Dynamin

A protein required for the completion of vesicle budding; its absence leads to the formation of coated pits that cannot pinch off.

Rab proteins

A family of proteins involved in the recognition and docking of transport vesicles with their target membrane.

v-SNAREs and t-SNAREs

Complementary proteins on the vesicle and target membrane, respectively, that interact to pull the membranes together for fusion.

N-linked oligosaccharides

Branched 14-sugar chains attached to the asparagine in the sequence Asn-X-Ser/Thr inside the endoplasmic reticulum.

ER retention signal

A signal on proteins normally residing in the ER lumen that allows them to be captured in the Golgi and returned to the ER.

Chaperone proteins

Proteins that help misfolded proteins fold properly or bind to them to retain them in the ER for eventual export and degradation in the cytosol.

Unfolded protein response (UPR)

A cellular response activated by sensors for misfolded proteins that results in the expanded production of ER membrane and chaperone proteins.

Protein translocator

An ER membrane component through which the polypeptide chain threads as it is being translocated into the lumen.

Signal peptidase

An enzyme located in the ER lumen that cleaves the signal sequence from a protein after translocation has initiated.