Posttranslational maturation of the invasion acyl carrier protein of salmonella enterica serovar Typhimurium requires an essential phosphopantetheinyl transferase of the fatty acid biosynthesis pathway

Abstract

Salmonella pathogenicity island 1 (SPI-1) carries genes required for the formation of a type 3 secretion system, which is necessaryfor the invasion process of Salmonella. Among the proteins encoded by SPI-1 is IacP, a homolog of acyl carrier proteins.Acyl carrier proteins are mainly involved in fatty acid biosynthesis, and they require posttranslational maturation by addition ofa 4=-phosphopantetheine prosthetic group to be functional. In this study, we analyzed IacP maturation in vivo. By performingmatrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectrometry analysis of intact purified proteins,we showed that IacP from Salmonella enterica serovar Typhimurium was matured by addition of 4=-phosphopantetheine to theconserved serine 38 residue. Therefore, we searched for the phosphopantetheinyl transferases in charge of IacP maturation. Abacterial two-hybrid approach revealed that IacP interacted with AcpS, an enzyme normally required for the maturation of thecanonical acyl carrier protein (ACP), which is involved in fatty acid biosynthesis. The creation of a conditional acpS mutant thendemonstrated that AcpS was necessary for the maturation of IacP. However, although IacP was similar to ACP and matured byusing the same enzyme, IacP could not replace the essential function of ACP in fatty acid synthesis. Hence, the demonstrationthat IacP is matured by AcpS establishes a cross-connection between virulence and fatty acid biosynthesis pathway. © American Society for Microbiology 2013.