Question

What two classes of enzymes are very common in signal transduction pathways, and why?

Answer 1

Two classes of enzymes in signal transduction pathways are 1. Protein kinases and 2. phosphatases

Activation of cell-surface receptors leads to changes in protein phosphorylation through the activation of protein kinase. There are many types of protein kinases involved in signal transduction. They all have the same basic catalytic activity: they add a phosphate group to an amino acid in a target protein. The phosphate is provided by ATP. Protein kinases can be classified by the types of amino acids that they phopshorylate in the protein target. Five groups of protein kinases are distinguished by the types of amino acid targets: protein serine/threonine kinases, protein tyrosine kinases, dual specificity kinases, histidine kinases, aspartate kinases.

Protein kinases may be membrane-bound or cytosolic on the basis of their location in the cell. Cytosolic protein kinases are most often Ser/Thr protein kinases.

The activity of protein kinases is opposed by the activity of protein phosphatases, which remove remove phosphate phosphate groups from specific substrate proteins. Depending on structural parameters, the protein phosphatase family is classified into subfamilies: Ser/Thr-specific phosphates, phosphotyrosine phosphatases, Thr/Tyr-specific phosphatases, prokaryotic phosphohistidine and phosphoaspartate phosphatases.