Protein targeting

Protein targeting or protein sorting is the biological mechanism by which proteins are transported to their correct destinations within or outside the cell. Proteins can be targeted to the inner cell or cell membrane, organelles of the cell, or to exterior of the cell via secretion.

Overview

Protein targeting occurs post-translationally for most proteins, although some proteins may be directed to specific locations while they are being synthesized (co-translationally). The targeting process is usually specified by the amino acid sequence of the protein itself, which can contain targeting signals for various cellular compartments.

Mechanisms

Co-translational targeting

Co-translational targeting begins while the protein is still being synthesized. It is associated with proteins that are destined for the endoplasmic reticulum, including those that will be secreted from the cell, and proteins that will reside in the plasma membrane.

Post-translational targeting

Post-translational targeting occurs after the protein has been completely synthesized. It is associated with proteins that will reside in a number of different cellular compartments, including the mitochondria, chloroplasts, peroxisomes, and the nucleus.

Protein targeting signals

Protein targeting signals, or signal sequences, are the "addresses" that direct proteins to their correct location. These are usually found at the beginning (N-terminus) of the protein sequence, but can also be found at the end (C-terminus), or internally.

See also

• Signal peptide
• Signal recognition particle
• Translocon
• Sec61
• TOMM20
• TIMM23

References

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  Gunter Blobel, Nobel Prize winner for discoveries in protein targeting

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  General overview of protein targeting

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  Overview of proteins targeted to the mitochondria

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  Carrier pathway for proteins to inner membrane

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  Inner membrane and matrix protein targeting

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  Protein targeting to the thylakoid membrane in chloroplasts

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  Peroxisome protein targeting