BIOL 4004 Module 6 Flashcards

AAA-ATPase

ATPase which provides energy for the retrotranslocation of misfolded proteins from the ER to the cytosol.

Acetyl-CoA ligase

Enzyme which 'activates' fatty acids by the addition of CoA.

Acyl transferase

Enzyme which catalyzes the attachment of Co-A-linked fatty acids to glycerol 3-phosphate.

BiP

Hsp70-like chaperone protein, located on the lumenal side of the ER membrane, which pulls proteins through the protein translocator via ATP-driven cycles of binding and release. This protein also functions as a chaperone protein which recognizes and binds

Calnexin

Membrane-bound ER chaperone protein which binds to the carbohydrate domains of unfolded ER proteins, preventing the proteins from leaving the ER.

Calreticulin

Soluble ER chaperone protein which binds to the carbohydrate domains of unfolded ER proteins, preventing the proteins from leaving the ER.

Chaperone proteins

Proteins which bind to other proteins to prevent them from folding, or to help them fold correctly.

Co-translational translocation

The simultaneous translation and translocation of a protein into the ER.

Cristae

Invaginations of the mitochondrial inner membrane.

Cytoplasm

Portion of a cell located outside of the nucleus, it includes the cytosol and organelles.

Dolichol

Membrane lipid on which an N-linked oligosaccharide precursor is first assembled before being transferred to the asparigine residue of an ER protein.

E3 ubiquitin ligase

Enzyme which attaches polyubiquitin tags to unfolded proteins as they exit a protein translocator and enter the cytosol, thus marking the protein for destruction by proteasomes.

Endoplasmic reticulum (ER)

Network of branching, interconnecting tubules and flattened sacs that extends throughout the cytosol.

ER cisternal space (ER lumen)

The continuous space between the two nuclear membranes and the two ER membranes.

ER resident proteins

Proteins that are retained and function within the ER.

ER retention signal

Four amino acid sequence at the C-terminal of a protein which prevents it from being translocation from the ER to other organelles.

ER signal peptidase

Enzyme, closely associated with the ER protein translocator, which cleaves ER signal sequences from translocating proteins.

Flippase

Head-group specific lipid translocator found in the plasma membrane, it flips phosphatidylserine and phosphatidylethanolamine directionally from the extracellular leaflet to the cytosolic leaflet, resulting in an asymmetric lipid bilayer.

Free ribosomes

Ribosomes, unattached to a membrane, which function in the synthesis of cytosolic proteins.

Gated transport

The selective movement of proteins between the cytosol and nucleus.

Glucosidase

Enzyme which cleaves terminal glucose residues from N-linked oligosaccharides in the ER.

Glucosyl transferase

ER enzyme which adds a glucose residue to ER proteins that are not properly folded.

Glycosylphosphatidyl-inositol (GPI) anchor

A glycolipid which can be attached to the C-terminus of a protein in the ER lumen; when transported to the plasma membrane the protein will be displayed on the cell surface.

Golgi apparatus

Organelle composed of stacks of disc-like compartments called cistenae; functions in the modification of proteins and lipids received from the ER, and transport of these molecules to various cellular locations.

Lysosomes

Organelle which functions in the degradation of intracellular and extracellular macromolecules, as well as the degradation of other organelles.

Membrane-bound ribosomes

Ribosomes attached to the cytosolic side of the ER membrane.

Mitochondria

Double membrane organelle which contains its own genome and carries out a variety of functions, including the production of ATP.

Mitochondrial Hsp70

Part of the TIM translocator, this chaperone protein binds to imported proteins as they emerge from the TIM channel, and helps 'pull' the protein into the matrix space using the energy of ATP hydrolysis.

N-glycanase

Enzyme which removes oligosaccharides chains from ER proteins that have been retrotranslocated into the cytosol.

N-linked oligosaccharides

Oligosaccharides covalently linked to asparagine residues of proteins.

NPC proteins (nucleoporins)

Proteins which form nuclear pore complexes, they are composed of repetitive domains and are orientated symmetrically across the nuclear envelope.

Nuclear basket

Network of fibrils which protrude from nuclear pore proteins into the nucleus and cytosol.

Nuclear export receptors (exportins)

Receptors which bind to nuclear export signals and NPC proteins; they function in the translocation of proteins from the nucleus to the cytosol.

Nuclear export signals

Sorting signals used to direct the translocation of proteins and protein complexes from the nucleus to the cytosol.

Nuclear import receptors (importins)

Receptors which bind to NLS and NPC proteins; they function in the translocation of proteins from the cytosol to the nucleus.

Nuclear lamina

Network of nuclear lamin proteins which gives shape and stability to the envelope.

Nuclear localization signals (NLS)

Sorting signals used to direct the translocation of proteins and protein complexes from the cytosol to the nucleus.

Nuclear pore complexes (NPCs)

Arrangement of protein subunits which function to regulate the gated transport of proteins between the cytosol and the nucleus.

Oligosaccharyl transferase

Enzyme that transfers a precursor oligosaccharide from membrane-bound dolichol to certain asparagine residues of proteins imported into the ER.

O-linked oligosaccharide

Oligosaccharide linked to an hydroxyl group of serine, threonine or hydroxyl-lysine.

Organelles

Membrane bound compartments within the cytosol.

OXA complex

Mitochondrial inner membrane translocator which mediates the insertion of mitochondrial encoded proteins and nuclear-encoded matrix proteins into the inner membrane.

PERK kinase, ATF6 and IRE1 kinase

Three ER membrane proteins which sense, and are activated by, an accumulation of unfolded proteins. These proteins carry out the unfolded protein response.

Peroxins

Proteins which form perioxisome protein translocators.

Peroxisomes

Organelle which contains high concentrations of oxidative enzymes.

Phosphatidic acid

This phospholipid precursor is formed by the attachment of glycerol 3-phosphate to two membrane fatty acids.

Phospholipid exchange proteins (phospholipid transfer proteins)

Water soluble carrier proteins involved in the transport of lipids from the ER to mitochondria.

Polyribosome

Multiple ribosomes attached to a single mRNA.

Porins

Beta-barrel proteins which form large pores in the outer mitochondrial membrane, making it freely permeable to inorganic ions and metabolites.

Post-translational translocation

The import of proteins into organelles after their translation is completed in the cytosol.

Proteasomes

Cytosolic structures where poly-ubiquitylated proteins are degraded.

Protein disulfide isomerase (PDI)

Enzyme which catalyzes the oxidation of free sulfhydryl groups of cysteines residues to form disulfide bonds.

Protein translocation

Movement of proteins from the cytosol to mitochondria, peroxisomes and the ER via the recognition of sorting signals by transmembrane protein translocators.

Protein translocators

Transmembrane, multiprotein complexes which mediate the movement of proteins across membranes.

Ran GTPase

GTPase (molecular switch) which functions in the regulation of nuclear import and export.

Ran GTPase-activating protein (Ran-GAP)

Cytosolic protein which catalyzes the hydrolysis of Ran-bound GTP, converting Ran-GTP to Ran-GDP.

Ran Guanine Exchange Factor (Ran-GEF)

Nuclear protein which catalyzes the exchange of GCD for GTP, converting Ran-GDP to Ran-GTP.

Ran-specific regulatory proteins

Proteins which catalyze the conversion of Ran-GTPase between two states (bound GTP or bound GDP), e.g. Ran-GAP and Ran-GEF.

Retrotranslocation (dislocation)

Translocation of misfolded ER proteins back to the cytosol for degradation.

Rough endoplasmic reticulum (RER)

Organelle with membrane-attached ribosomes; site for the synthesis of protein destined for the Golgi, endosomes, lysosomes, plasma membrane and extracellular space.

SAM complex

Mitochondrial outer membrane complex which helps outer membrane ?-barrel proteins fold correctly.

Scramblase

Non-specific lipid translocator which flips phospholipids between membrane leaflets, resulting in an equal distribution between monolayers.

Sec61 complex

Protein complex which forms the aqueous core of ER protein translocators.

Signal patches

Sorting signals composed of multiple internal amino acid sequences that from a three-dimensional arrangement on the surface of a protein.

Signal sequences

Sorting signals composed of stretches of amino acids 15-60 residues in length.

Signal-recognition particle (SRP)

Ribonucleoprotein complex which binds to an ER signal sequence as it emerges from the ribosome, halts further translation, and guides the ribosome to receptors on the ER membrane.

Smooth endoplasmic reticulum (SER)

Organelle which is the site for the synthesis of most lipids, and storage of intracellular calcium.

Sorting receptors

Proteins which recognize sorting signals.

Sorting signals

Sequences that direct the delivery of a proteins to a specific cellular compartment; proteins without these sequences will remain in the cytosol.

SRP receptor

An ER transmembrane complex which binds to SRP, and brings the SRP-ribosome complex to an unoccupied protein translocator.

Start transfer signal

A protein sequence, usually a signal sequence, which binds to a protein translocator, triggering the start of protein translocation.

Stop transfer signal

Hydrophobic sequence that halts the translocation of a polypeptide chain through a membrane protein translocator.

TIM22 complex

Mitochondrial inner membrane protein translocator which mediates the insertion of some proteins into the inner membrane.

TIM23 complex

Mitochondrial inner membrane protein translocator, associated with mitochondrial HSP70, which transports some soluble proteins into the matrix space, and helps insert transmembrane proteins into the inner membrane.

TOM complex

Mitochondrial outer membrane protein translocator required for the translocation of all nuclear encoded mitochondrial proteins.

Translation pause domain

Domain on the SRP which causes a pause in translation by interfering with the binding of elongation factor.

Translocon

Complex of a protein translocator and associated proteins (e.g. oligosaccharide transferases, signal peptidases) that act to modify the translocating protein.

Unfolded protein response

This response to an accumulation of unfolded/misfolded ER proteins results in an increased transcription of genes involved in retrotranslocation and cytosolic protein degradation.

Zellweger syndrome

Inherited human disease caused by defects in the import of proteins to peroxisomes.