Structural Biochemistry/Proteins/Adenylation

Adenylation, also known as adenylylation or AMPylation, is the process of attaching an AMP molecule to a protein side chain by covalent bonding. It has two main functions: 1) to regulate enzyme activity via post-translational modification and 2) to produce unstable intermediates of a protein, peptide or amino acids to allow reactions that are not thermodynamically favored to occur.

Adenylation Applications
Adenylations has a particular application when it involves the adenylation of RNA. There is a known procedure that allows for RNA 5' adenylation using T4 DNA ligases. Basically this is an approach to adenylate RNA so that it becomes a 5',5'-adenyl pyrophosphoryl cap structure. This new adenylated RNA structure is desirable in the sense that it can investigate certain natural biochemical pathways that require such intermediates. The 5' adenylated RNA is also useful for a certain amount of in vitro selection procedures to identify nucleic acid enzymes that specificially use the 5' adenlyated RNA as a reactive RNA substrate. This is particularly favorable given that the adenylated RNA is considered a transition state molecule which has evolved to become the most favorable of states when it comes to enzyme substrate complexes. in other words, the adenylation of the 5' RNA allows for a better enzyme substrate complex due to its nature of being a transitional state substrate for biochemical pathways that wish to be observed. In addition to being a RNA substrate for selective catalysis reactions, there are also applications to RNA '5 capping and 5' labeling. It was shown in the "Efficient RNA5' adenylation by T4 DNa ligase to facilitate practical applications" paper that the protein enzyme T4 RNA ligase was used along with some DNA oligonucleotides to create a net transfer of the AMP group onto a monophosphorolyated terminus of the desired RNA substrate.

Enzyme Regulation
Glutamine synthetase regulation by adenylation

Formation of Unstable Intermediates
Carboxyl groups of small molecules or amino acids may be adenylated to form unstable intermediates as shown in the diagram to the left.

For many decades, the example of glutamine synthetase has been used to explain the principles of adenylation, but recent discoveries in adenylation of Rho and Rab GTPases have shown potential in revealing the other aspects of adenylation.