Structural characterization of TssL from Acinetobacter baumannii : a key component of the type VI secretion system

LOPEZ, JUVENAL; ESPINOSA, YANIS R.; RUIZ, FEDERICO M.; SANTILLANA, ELENA; ROMERO, ANTONIO; FERRARA, C. GASTÓN; FELDMAN, MARIO F.

JOURNAL OF BACTERIOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2020

0021-9193

The type VI secretion system (T6SS) is a complex molecular nanomachine used by Gram-negative bacteria to deliver diverse effectors into adjacent cells. A membrane complex (MC) anchors this transport system to the bacterial cell wall. One of the proteins forming the MC is TssL, a cytoplasmic protein bound to the inner membrane through a single transmembrane helix. Here, we report the structure of the cytoplasmic N-terminal region of TssL from Acinetobacter baumannii, a bacteria encoding in a single locus a secretion system that is a special case among others T6SSs. The protein structure, consisting of two antiparallel alpha-helical bundles connected by a short loop, reveals several interesting particularities when compared with homologues proteins from other organisms. In addition, we demonstrate the structural significance of residues Asp98 and Glu99, which are strongly conserved among T6SS-encoding Gram-negative bacteria. Mutations in these two residues strongly impact protein dynamics, expression and functionality. Our results improve our understanding of the T6SS of A. baumannii, which remains largely understudied, compared with that of other pathogens.