General principles of cellular communication

# 3 Proteins: major components of signalling pathways

Many signalling pathways, though by no means all, are composed entirely of proteins. To help you make sense of how signalling pathways work, some general principles governing proteins involved in signalling, their functions and their regulation, are reviewed here.

## Activity 3 Proteins

Why do you think proteins are particularly well suited for signal transduction?

## Answer

Proteins are capable of interacting in a highly specific manner with various ligands and also other proteins. These features are required to ensure fidelity in a signalling pathway. Also, the activity of proteins can be acutely modulated by altering their conformation (for example, by allosteric regulation and by covalent modification), thereby tuning the flow of information via signalling pathways.

## Activity 4 Protein–ligand interactions

What is the basis of the specificity exhibited by proteins in protein–ligand interactions?

## Answer

If you were thinking along the lines of the structure or conformation of the protein and its ligand, you would be on the right track. Protein–ligand interactions depend on the chemical and physical compatibility of the protein and its ligand and involve the formation of a variety of non-covalent interactions.

## Activity 5 non-covalent interactions

Which of the following are non-covalent interactions?

- hydrogen bond
- ionic bond
- hydrophobic interaction

## Answer

All of these are types of non-covalent interaction and they are all involved in protein–ligand interactions.

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