guanylated

Guanylated is the adjective used to describe a molecule, protein, or nucleic acid that has been modified by the covalent attachment of a guanylate (GMP) moiety. The process, guanylation, is typically mediated by guanylyltransferases, enzymes that transfer GMP from GTP to a substrate, releasing pyrophosphate.

Guanylation is most prominent in RNA biology via the 5' capping reaction. In eukaryotic and some viral systems, a guanylyltransferase transfers GMP from GTP to the 5' diphosphate end of a nascent pre-mRNA, generating a cap structure (GpppN), which is subsequently methylated to form the mature cap (m7GpppN). This cap protects RNA from degradation, aids in ribosome recognition, and regulates RNA processing.

Beyond RNA capping, guanylation can refer to the covalent attachment of GMP to other substrates, including proteins, in various enzymatic contexts. In these cases, the resulting guanylated substrate bears a GMP moiety that can influence function, interactions, or localization. Guanylation reactions are part of broader nucleotide-modification chemistry, and their occurrence is studied to understand post-transcriptional regulation, host-pathogen interactions, and enzymology of nucleotide transfer reactions.

Chemical details: the transfer usually involves activation of the substrate's terminal phosphate or diphosphate, followed by nucleophilic attack by an active-site residue on the substrate. The reaction liberates pyrophosphate and yields a stable GMP-conjugate.

In summary, guanylated describes entities bearing a GMP addition, most notably in RNA capping, but also in other guanylyltransferase-mediated modifications. The term emphasizes the presence of a guanylate group as a covalent modification rather than merely the binding of guanine-containing ligands.