Question

Describe the functions of the following proteins and how they modify other proteins to activate or inactivate these other protein’s enzymatic functions: 1)Kinases, 2)Phosphatases, 3)Acetyltransferases, 4)Methyltransferases.

Answer 1

1) Kinases:

Function: Transfer of phosphate group from a high energy molecules that donate phosphate, such as ATP to the substrate protein. This process is called phosphorylation.

Mechanism: Phosphorylation of Ser, Thr, Tyr and His in the protein such as receptors activates these proteins. Addition of phosphate to a non polar R-group of amino acid, changes the hydrophobic part of the protein to highly hydrophilic protein. This conformational change results in reversible activation and plays a major role in signal transduction.

2) Phosphatases:

  Function: Removal of phosphate group from a substrate protein by hydrolysis. This process is called dephosphorylation.

Mechanism: Dephosphorylation of amino acids in the proteins such as receptors deactivates these proteins. Removal of phosphate to a polar R-group of amino acid, changes the hydrophilic part of the protein to highly hydrophobic protein. This conformational change results in reversible deactivation and plays a major role in signal transduction.

3) Acetyltransferases:

Function: Transfer of acetyl group from a acetyl-group donor to the substrate, a process known as acetylation.

Mechanism: Acetylation is a post-translational modification. Addition of acetyl group to a positively charged amino acid, makes the protein neutral. Thus the change in charge of the protein leads to the conformational change. This reversible conformation involves in many function such as regulating accessibility of DNA by histone acetylation.

4) Methyltransferases:

Function: Transfer of methyl group from a acetyl-group donor to DNA, a process known as methylation.

Mechanism: Addition of methyl group to the DNA, regulates the transcription of the DNA region that is methylated.