Protein sorting is the mechanism by which cells transport proteins to the appropriate locations inside or outside the cell. Sorting signals contained within the protein direct it to targets like organelles, membranes, or out of the cell. Correct sorting is important for cell function, as errors can lead to disease. The major intracellular compartments and their relative volumes are the cytosol, mitochondria, ER, Golgi apparatus, nucleus, peroxisomes, lysosomes, and endosomes. Protein sorting involves transport of proteins from the cytosol to target locations directed by sorting signals like sequences for nuclear import, mitochondrial import, or ER import.

1. Shambhu Prasad.G.A
VII sem, M.Sc in Mol-Bio
-by

2. Protein targeting or protein sorting is the mechanism by which a cell
transports proteins to the appropriate positions in the cell or outside of it.
Sorting targets can be the inner space of an organelle, any of several interior
membranes, the cell's outer membrane, or its exterior via secretion. This
delivery process is carried out based on information contained in the protein
itself. Correct sorting is crucial for the cell; errors can lead to diseases.
Protein sorting and targeting

3. Intracellular
compartment
% of total cell
volume
Cytosol 54
Mittchondria 22
Rough ER
cisternae
9
Smooth ER
cisternae plus
Golgi cisternae
6
Nucleus 6
Peroxisome 1
Lysosomes 1
Endosomes 1
Relative volumes occupied by the major intracellular compartments in Liver Cell

4. Endomembrane System

6. Protein sorting: Protein molecules move from the cytosol to their target
organelles or cell surface directed by the sorting signals in the proteins.
Some typical signal sequences:
Import into nucleus: -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val-
Export from nucleus: -Leu-Ala-Leu-Lys-Leu-Ala-Gly-Leu-Asp-Ile-
Import into mitochondris: +H3N-Met-Leu-Ser-Leu-Arg-Gln-Ser-Ile-Arg-Phe-Phe-
Lys-Pro-Ala-Thr-Arg-Thr-Leu-Cys-Ser-Ser-Arg-Tyr-Leu-Leu-
Import into peroxisomes: -Ser-Lys-Leu-COO-
Import into ER: +H3N-Met -Met-Ser-Phe-Val-Ser-Leu-Leu-Leu-Val-Gly-Ile-Leu-
Phe-Try-Ala-Thr-Glu-Ala-Glu-Gln-Leu-Thr-Lys-Cys-Glu-Val-Phe-Gln-
Return to ER: -Lys-Asp-Glu-Leu--COO-
Positively charged amino acids
Hydrophobic amino acids

7. Transport of protein to
NUCLEUS

8. The transport of Proteins
into MITOCHONDRIA &
CHLOROPLAST

9. Transport of proteins into
PEROXISOMES

10. ENDOPLASMIC RETICULUM

11. INTRACELLULAR VESICULAR TRAFFIC
Endomembrane system

13. Structure of GOLGI-COMPLEX

14. Transpot of newly synthesized lysosomal hydrolases to LYSOSOMES
The mannose 6-phosphate pathway: M-6-P
receptor binds its specific oligo. at pH6.5-6.7 in TGN
and releases it at pH6.0 in late endosomes.

16. Motar proteins mediate
movement of vesicles
along MICRO TUBULES
kinesin dynein

17. References :
http://www.mblab.gla.ac.uk/~julian/Dict.html
http://www.ncsu.edu/imse/1/cellbiology.
Molecular Biolgy of the Cell;2004 B.Alberts, D.Bray, J.Lewis, M.Raff, K.Roberts
& J.D.Watson. Garland Publishers, New York and London.
Molecular Cell Biology;2002 Lodish.H.F, Berk.A, Matsudaira.P, Kaiser.C.A,
Kraeger.M,Scot.M.P, Zipursky.S.L, Darnel.J ; W.H.Freeman and co., Publishers.

18. THANK YOU ALL