M6P is a key targeting signal for acid hydrolase precursor proteins that are destined for transport to lysosomes.

Specifically, in a reaction involving uridine diphosphate (UDP) and N-acetylglucosamine, the enzyme N-acetylglucosamine-1-phosphate transferase catalyzes the N-linked glycosylation of asparagine residues with M6P.

Once appropriately marked with the M6P targeting signal, these proteins are moved to the trans-Golgi network.

There, the M6P moiety is recognized and bound by mannose 6-phosphate receptor (MPR) proteins at pH 6.5–6.7.

[1] The MPRs are packed into vesicles that bud off the late endosome and return to the trans-Golgi network.