# Interaction between bacterial phytochromes Agp1 and Agp2 of Agrobacterium fabrum by fluorescence resonance energy transfer and docking studies

## TL;DR

This study explores how two bacterial proteins, Agp1 and Agp2, interact to control DNA transfer and conjugation in Agrobacterium fabrum.

## Contribution

The study reveals the specific interaction mechanism between Agp1 and Agp2 using FRET and docking models.

## Key findings

- FRET efficiencies increased from position 122 to 545 of Agp1.
- Agp2's PCM showed FRET signals, while Agp1's PCM did not.
- Arg83 of Agp2 is specifically evolved to interact with Agp1.

## Abstract

Phytochromes are biliprotein photoreceptors found in bacteria, fungi, and plants. The soil bacterium Agrobacterium fabrum has two phytochromes, Agp1 and Agp2, which work together to control DNA transfer to plants and bacterial conjugation. Both phytochromes interact as homodimeric proteins. For fluorescence resonance energy transfer (FRET) measurements, various Agp1 mutants and wild‐type Agp2 were labeled with specific fluorophores to study their interaction. FRET efficiencies rose from position 122 to 545 of Agp1. The photosensory chromophore module (PCM) of Agp1 did not show a FRET signal, but the PCM of Agp2 did. Docking models suggest that Agp1 and Agp2 interact with their histidine kinase and PCM perpendicular to each, around 45 amino acids of Agp1 or Agp2 are involved.

The interaction between Agrobacterium fabrum phytochromes Agp1 and Agp2 was studied using FRET. Full‐length and truncated proteins with varied label positions provided spatial insights, narrowing down from many docking models to three. These models explain Agp2's reduction in Agp1 autophosphorylation, with Arg83 of Agp2 specifically evolved to interact with Agp1, unlike Agp2 in species without Agp1.