Adenylation

Adenylation, or adenylylation, is the enzymatic process in which an adenosine monophosphate (AMP) group is transferred to a substrate. This transfer typically forms an adenylylated intermediate that participates in subsequent chemical steps, and many reactions use ATP as the donor of the AMP moiety.

Adenylation is a common activation step in metabolism and signaling. In protein synthesis, aminoacyl-tRNA synthetases activate amino acids by forming aminoacyl-AMP before the amino acid is transferred to tRNA. In ubiquitin signaling, ubiquitin-activating enzymes (E1) adenylate ubiquitin to form a ubiquitin-AMP intermediate, which then reacts to form a thioester bond with the enzyme. Other nucleotidyltransferases perform similar transfers of AMP to diverse substrates, enabling downstream reactions such as ligation, activation, or tagging.

In RNA biology, adenylation is also used to describe the addition of adenine nucleotides to RNA, most prominently the polyadenylation of eukaryotic mRNA. Polyadenylation adds a poly(A) tail at the 3' end, a modification that influences RNA stability, export from the nucleus, and translational efficiency. Poly(A) polymerases catalyze this process by adding multiple AMP units from ATP to the RNA terminus.

Enzymes that catalyze adenylation are often referred to as adenylyltransferases. The term encompasses a broad family of enzymes, collectively playing essential roles in protein maturation, signaling, RNA processing, and metabolism.