lecture 6 Protein Transport and Translocation Mechanisms

Vocabulary flashcards focused on key terms and definitions related to protein transport and translocation mechanisms.

Signal Recognition Particle (SRP)

A ribonucleoprotein that mediates the targeting of proteins to the endoplasmic reticulum (ER) by binding to the ribosome and the signal sequence.

Polyribosome

A complex of multiple ribosomes that are simultaneously translating a single mRNA molecule.

Translocator

A protein complex that forms a water-filled channel in the endoplasmic reticulum membrane that facilitates the translocation of polypeptides across the membrane.

Sec61 complex

Built from 3 subunits conserved from bacteria to eukaryotes that are the core component of the ER translocator responsible for transporting polypeptides across the ER membrane. Consists of 10 helices surrounding a central channel

Cotranslational translocation

The process by which proteins are simultaneously synthesized and inserted into the ER membrane.

Post-translational translocation

The process of transporting fully synthesized proteins into the ER after their synthesis in the cytosol.

Chaperone proteins

Proteins that assist in the proper folding and assembly of polypeptides within the ER.

Hydrophobic segment

A region of a transmembrane protein that is recognized by the SRP and facilitates insertion into the ER membrane.

Signal peptide

A short peptide sequence that directs the transport of the polypeptide to the ER and engages the translocator.

Oligosaccharide

A carbohydrate molecule that is covalently attached to proteins in the ER, often playing a role in protein folding.

Glycosylation

The covalent attachment of sugars to proteins, a critical process for protein maturation and function.

Calnexin

A chaperone protein in the ER that assists in the folding process of newly synthesized glycoproteins.

Nuclear pore complex (NPC)

A large protein complex that spans the nuclear envelope, allowing selective transport of proteins and RNA between the nucleus and cytosol.

Nuclear localization signal (NLS)

An amino acid sequence that directs proteins to the nucleus through recognition by import receptors.

GTPase Ran

A molecular switch that regulates nuclear transport, existing in GTP-bound (active) and GDP-bound (inactive) forms.

Karyopherins

Proteins that mediate the transport of cargo proteins into and out of the nucleus by recognizing nuclear localization signals.

Import receptor

A transport receptor that binds to cargo proteins with NLSs for import into the nucleus.

Export receptor

A transport receptor that facilitates the export of cargo proteins from the nucleus to the cytoplasm.

Phosphatase calcineurin

An enzyme that dephosphorylates NF-AT, enabling its nuclear localization during T cell activation.

Sterol response element binding protein (SREBP)

A transcription factor that regulates cholesterol biosynthesis in response to cellular cholesterol levels.

Cytosol

The liquid component of the cytoplasm, excluding organelles and membrane-bound structures.

Endoplasmic reticulum (ER)

An organelle involved in the synthesis, folding, modification, and transport of proteins.

Transmembrane protein

Proteins that span the biological membrane and are usually processed in the ER before being sent to their final destinations.

Nuclear lamina

A meshwork of protein filaments within the nucleus that provides structural support and organizes chromatin.

AAA-ATPase

A family of proteins that utilize ATP hydrolysis to promote unfolding and translocation of substrates across membranes.

Glucosyl transferase

An enzyme that re-adds glucose residues to glycoproteins, facilitating their association with chaperones for folding.