Guanylating

Guanylating is the covalent attachment of a guanylyl group (the GMP moiety) to a substrate, typically via transfer from guanosine triphosphate (GTP). The reaction is catalyzed by enzymes known as guanylyltransferases and often releases pyrophosphate as a byproduct. Guanylation encompasses several related biological processes in which a guanylyl group is added to a molecule such as RNA, proteins, or small metabolites.

A prominent example is RNA capping in eukaryotes and some viruses. An RNA guanylyltransferase transfers GMP from GTP to the 5' end of a nascent RNA, producing a cap structure (GpppN). Further methylation yields the mature m7G cap, which is important for mRNA stability, export, and translation initiation.

Guanylation also appears as covalent post-translational modification of proteins in certain contexts, referred to as protein S-guanylation or N-guanylation, where a GMP moiety becomes attached to amino acid side chains such as cysteine or lysine. This modification is associated with redox signaling and can modulate protein activity or interactions, though the prevalence and functional consequences are still being investigated.

Guanylation can also describe the formation of guanylated intermediates or conjugates in metabolic pathways, where a guanylyl group is transferred to a carrier molecule or small substrate to enable subsequent transformations.

Overall, guanylating describes the chemical process of transferring a guanylyl group to a substrate, shaping various molecular functions from RNA processing to potential regulatory protein modifications.