Transcript Lecture 7: Protein Sorting

Roadmap of
protein traffic
inside cell
Two ways in which a sorting signal can be
built into a protein
Some typical signal sequences
Nuclear Pore complexes perforate the nuclear
envelope
Nuclear pore complexes
Nuclear side of the nuclear envelope
Face on view of nuclear complexes without the
membrane
Side view of 2 nuclear pore complexes
Transport through nuclear pore complexes
occurs through free diffusion and active transport
Nuclear import signal direst proteins to the nucleus
Single amino acid mutation in signal will prevent
import into the nucleus
Nuclear import receptors bind to nuclear porins
and nuclear localization signal of cargo protein
Different nuclear localization signals bind different import receptors
Ran GTP provides energy for nuclear protein import
Ran-GTP controls cargo loading and unloading
Transmembrane transport into the mitochondria
and chloroplasts
Subcompartments of mitochondria and
chloroplasts
Signal sequence for mitochondrial import
red = positively charged
yellow = nonpolar
Signal sequence for mitochondrial import can
form amphipathic α - helix
α - helix is recognized by receptor proteins
Protein translocators in mitochondrial membrane
Protein import by mitochondria
DVD Clip 55
Protein transport into the peroxisomes
Roadmap of
protein traffic
inside cell
Insertion of rhodopsin into the ER membrane
Most proteins in the ER
are glycosylated
Proteins in cytosol are
rarely glycosylated
original precursor
oligosaccharide added
to most proteins in the ER
Protein glycosylation in the rough ER
Oligosaccharides are used as tags to mark the
state of protein folding
Misfolded proteins are exported from ER and
destroyed