A new target of multiple lysine methylation in bacteria

The methylation of ε-amino groups in protein lysine residues is an important posttranslational modification in eukaryotes, influencing various biological processes. In prokaryotes, this modification has been less studied, but recent findings suggest its role in bacterial immune evasion and host cell adhesion. Here, we analyzed Acinetobacter sp. Tol 5 cell surface proteins using LC‒MS, discovering that lysine residues of its trimeric autotransporter adhesin (TAA), AtaA, are specifically methylated. Over 130 of 232 lysine residues in AtaA were methylated. We identified the outer membrane protein lysine methyltransferase (OM PKMT) KmtA, responsible for the methylation. Bioinformatic analysis revealed the wide distribution of OM PKMT genes among gram-negative bacteria, including pathogens with TAAs that promote infection, such as Burkholderia mallei and Haemophilus influenzae. Clustering analysis suggested that KmtA is a new type of OM PKMT. Deletion of Tol 5 KmtA increased AtaA on the cell surface, enhancing adhesion and slowing growth.