Guanylation

Guanylation is a biochemical process in which a guanine-containing moiety, most commonly guanosine monophosphate (GMP), is covalently attached to a substrate. The reaction is typically catalyzed by enzymes called guanylyltransferases, which use guanosine triphosphate (GTP) as the donor of the GMP group. Guanylation can create a stable covalent bond between GMP and the substrate, forming a guanylated product.

A well-characterized example is the formation of the 5' cap on eukaryotic mRNA. RNA guanylyltransferases transfer GMP from GTP to the 5'-diphosphate end of a nascent RNA, producing a cap structure (GpppN) that is subsequently methylated. The cap is important for RNA stability, nuclear export, and translation initiation.

In addition to RNA capping, guanylation has been described as a post-translational modification of proteins in some contexts. One form, known as S-guanylation, involves the covalent modification of cysteine residues with a GMP moiety under oxidative or nitrosative stress, with potential effects on protein function and signaling. These protein guanylation events are less well understood than RNA capping and are an active area of study.

Research on guanylation covers enzymology, RNA biology, and redox signaling. Key concepts include guanylyltransferases, the formation of enzyme–GMP intermediates, and the recognition of guanylated substrates. Analytical approaches include biochemical assays and mass spectrometry to detect GMP modifications and cap structures on RNA.