An acetyltransferase effector conserved across
Legionella
species targets the eukaryotic eIF3 complex to modulate protein translation
Authors: Syriste Lukas , Patel Deepak T. , Stogios Peter J. , Skarina Tatiana , Patel Dhruvin , Savchenko Alexei 
Published: February 2024

The survival of
Legionella
spp. as intracellular pathogens relies on the combined action of protein effectors delivered inside their eukaryotic hosts by the Dot/Icm (
d
efective in
o
rganelle
t
rafficking/
i
ntra
c
ellular
m
ultiplication) type IVb secretion system. The specific repertoire of effector arsenals varies dramatically across over 60 known species of this genera with
Legionella pneumophila
responsible for most cases of Legionnaires’ disease in humans encoding over 360 Dot/Icm effectors. However, a small subset of “core” effectors appears to be conserved across all
Legionella
species raising an intriguing question of their role in these bacteria’s pathogenic strategy, which for most of these effectors remains unknown.
L. pneumophila
Lpg0103 effector, also known as VipF, represents one of the core effector families that features a tandem of Gcn5-related N-acetyltransferase (GNAT) domains. Here, we present the crystal structure of the Lha0223, the VipF representative from
Legionella hackeliae
in complex with acetyl-coenzyme A determined to 1.75 Å resolution. Our structural analysis suggested that this effector family shares a common fold with the two GNAT domains forming a deep groove occupied by residues conserved across VipF homologs. Further analysis suggested that only the C-terminal GNAT domain of VipF effectors retains the active site composition compatible with catalysis, whereas the N-terminal GNAT domain binds the ligand in a non-catalytical mode. We confirmed this by
in vitro
enzymatic assays which revealed VipF activity not only against generic small molecule substrates, such as chloramphenicol, but also against poly-L-lysine and histone-derived peptides. We identified the human eukaryotic translation initiation factor 3 (eIF3) complex co-precipitating with Lpg0103 and demonstrated the direct interaction between the several representatives of the VipF family, including Lpg0103 and Lha0223 with the K subunit of eIF3. According to our data, these interactions involve primarily the C-terminal tail of eIF3-K containing two lysine residues that are acetylated by VipF. VipF catalytic activity results in the suppression of eukaryotic protein translation
in vitro
, revealing the potential function of VipF “core” effectors in
Legionella
’s pathogenic strategy.

IMPORTANCE

By translocating effectors inside the eukaryotic host cell, bacteria can modulate host cellular processes in their favor.
Legionella
species, which includes the pneumonia-causing
Legionella pneumophila,
encode a widely diverse set of effectors with only a small subset that is conserved across this genus. Here, we demonstrate that one of these conserved effector families, represented by
L. pneumophila
VipF (Lpg0103), is a tandem Gcn5-related N-acetyltransferase interacting with the K subunit of human eukaryotic initiation factor 3 complex. VipF catalyzes the acetylation of lysine residues on the C-terminal tail of the K subunit, resulting in the suppression of eukaryotic translation initiation factor 3-mediated protein translation
in vitro
. These new data provide the first insight into the molecular function of this pathogenic factor family common across
Legionellae
.