Protein Targeting

Abstract

Protein sorting is the process by which cellular proteins, both newly synthesised and recycling, are directed to the appropriate intracellular compartments in which they will perform their function. This process relies upon the targeting signals that are found within each protein. These specific signals can be integrally encoded within the polypeptide sequence or require post-translational modification of the protein. Targeting signals direct the interaction of proteins with a multitude of accessory factors to ensure the correct delivery of proteins to their appropriate destinations within each cell. Many proteins have multiple targeting signals that are interpreted hierarchically in cellular compartments. Changes in the expression of either the targeting signals or their recognition factors alter the targeting of proteins in different cell types or in response to physiological cues.

Key Concepts:

• Protein targeting signals can be encoded within the polypeptide chain or can be post-translational modifications or patches.

• Targeting signals are recognised by cellular factors that direct proteins to their proper site of function.

• Many proteins have multiple targeting signals.

• The relative strength of targeting signals can change based on post-translational modifications such as phosphorylation or accessibility to recognition factors at different locations within cells.

• Differences in the expression of targeting signals or recognition factors can result in cell-type dependent, developmental, or acute changes in protein targeting.