The Diverse Functional Roles of Elongation Factor Tu (EF-Tu) in Microbial Pathogenesis

Abstract

Elongation factor thermal unstable Tu (EF-Tu) is a G protein that catalyzes the binding of aminoacyl-tRNA to the A-site of the ribosome inside living cells. Structural and biochemical studies have described the complex interactions needed to effect canonical function. However, EF-Tu has evolved the capacity to execute diverse functions on the extracellular surface of both eukaryote and prokaryote cells. EF-Tu can traffic to, and is retained on, cell surfaces where can interact with membrane receptors and with extracellular matrix on the surface of plant and animal cells. Our structural studies indicate that short linear motifs (SLiMs) in surface exposed, non-conserved regions of the molecule may play a key role in the moonlighting functions ascribed to this ancient, highly abundant protein. Here we explore the diverse moonlighting functions relating to pathogenesis of EF-Tu in bacteria and examine putative SLiMs on surface-exposed regions of the molecule.

Keywords: EF-Tu; adhesion; bacteria; chaperone activities; moonlighting.

FIGURE 1

The canonical role of EF-Tu in translation. Structures sourced from protein databank (PDB), accession numbers 1DG1, 5OPD, 1B23, 4PC7, 1EFT, 1EFT. EF-Ts monomer structure obtained using Phyre2.

FIGURE 2

Moonlighting functions of prokaryote EF-Tu. (A) (1) EF-Tu binds immune system regulators such as Factor H, substance P and plasminogen (and enhancing its conversion to plasmin), increasing virulence and immune system evasion. (2) EF-Tu stimulates both host innate and humoral immune responses. (3) Antibodies against EF-Tu decrease bacterial load and offer at least partial protection against some bacterial infections. (B) (4) EF-Tu binding to fibronectin facilitates invasion into host cells. EF-Tu also binds to other extracellular matrix (ECM) proteins, such as glycosaminoglycans, facilitating adhesion. (C) (5) EF-Tu binds MreB and facilitates production of MreB filaments that regulate cell shape. (D) (6) EF-Tu undergoes proteolytic processing and EF-Tu fragments also bind ECM proteins. Furthermore, these fragments may act as molecular decoys to help evade immune detection.

FIGURE 3

Basic amino acid residue clusters that reside within EF-Tu molecules that moonlight in prokaryotes. An exposed basic amino acid cluster (blue bar) with a putative P:P interaction sites (green circle) is present at the N-termini of moonlighting EF-Tu examples from both Gram positive and Gram-negative bacteria. However, only the Gram-positive bacteria appear to have a consensus heparin binding motif (red bar) and only in B. subtilis is this motif predicted to be solvent accessible (solid red bar). The remaining basic residue clusters are predicted to be at least partial buried.

FIGURE 4

N-termini basic residue cluster logo. The logo is representative of EF-Tu molecules derived from 17 prokaryote species.