The modification of serine to N-[5-(6-O-seryl-beta-glucosyl)-2,3-dihydroxybenzoyl]-O-[N-(2,3-dihydroxybenzoyl)-O-[N-(2,3-dihydroxybenzoyl)seryl]seryl]serine as found in microcin E492 produced from the mceA gene in plasmid pJAM229 of the E. coli VCS257 strain and the K. pneumoniae RYC492 strain.