# Experimental Approaches to Visualize Effector Protein Translocation During Host‐Pathogen Interactions

## TL;DR

This review discusses methods to visualize how bacteria deliver proteins into host cells, helping understand their role in disease.

## Contribution

The paper summarizes experimental approaches for analyzing effector protein translocation at the single molecule level.

## Key findings

- Various methods allow visualization of effector translocation from static to dynamic live-cell imaging.
- Recent approaches enable real-time tracking of effector proteins in living cells.
- The review highlights advantages, limitations, and open questions in the field.

## Abstract

Bacterial pathogens deliver effector proteins into host cells by deploying sophisticated secretion systems. This effector translocation during host‐pathogen interactions is a prerequisite for the manipulation of host cells and organisms and is important for pathogenesis. Analyses of dynamics and kinetics of translocation, subcellular localization, and cellular targets of effector proteins lead to understanding the mode of action and function of effector proteins in host‐pathogen interplay. This review provides an overview of biochemical and genetic tools that have been developed to study protein effector translocation qualitatively or quantitatively. After introducing the challenges of analyses of effector translocation during host‐pathogen interaction, we describe various methods ranging from static visualization in fixed cells to dynamic live‐cell imaging of effector protein translocation. We show the main findings enabled by the approaches, emphasize the advantages and limitations of the methods, describe recent approaches that allow real‐time tracking of effector proteins in living cells on a single molecule level, and highlight open questions in the field to be addressed by application of new methods.

Translocation of effector proteins is a key virulence trait of many pathogenic bacteria. Various strategies were developed to visualize the translocation of effector proteins, and this review summarizes experimental approaches for analyses of translocation towards localization, kinetics, and dynamics on single molecule level.