Rho-modifying bacterial protein toxins from Photorhabdus species

• Entomopathogenic Photorhabdus species produce numerous protein toxins.
• Photorhabdus luminescens Tc complex toxins ADP-ribosylate Rho and actin and cause clustering of the actin cytoskeleton.
• Photorhabdus asymbiotica toxin PaTox inactivates Rho proteins by N-acetyl-glucosaminylation of a tyrosine residue.
• PaTox activates heterotrimeric G proteins Gq and Gi by deamidation of a glutamine residue involved in GTP hydrolysis.
• Identification of a helical subdomain involved in membrane binding of PaTox glycosyltransferase.

Photorhabdus bacteria live in symbiosis with entomopathogenic nematodes. The nematodes invade insect larvae, where they release the bacteria, which then produce toxins to kill the insects. Recently, the molecular mechanisms of some toxins from Photorhabdus luminescens and asymbiotica have been elucidated, showing that GTP-binding proteins of the Rho family are targets. The tripartite Tc toxin PTC5 from P. luminescens activates Rho proteins by ADP-ribosylation of a glutamine residue, which is involved in GTP hydrolysis, while PaTox from Photorhabdus asymbiotica inhibits the activity of GTPases by N-acetyl-glucosaminylation at tyrosine residues and activates Rho proteins indirectly by deamidation of heterotrimeric G proteins.