Shambhu Prasad.G.A

VII sem, M.Sc in Mol-Bio

-by

Protein targeting or protein sorting is the mechanism by which a celltransports 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

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

Endomembrane System

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

Transport of protein to NUCLEUS

The transport of Proteins into MITOCHONDRIA & CHLOROPLAST

Transport of proteins into PEROXISOMES

ENDOPLASMIC RETICULUM

INTRACELLULAR VESICULAR TRAFFIC

Endomembrane system

Structure of GOLGI-COMPLEX

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.

Motar proteins mediate movement of vesicles along MICRO TUBULES

kinesin dynein

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.

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