A synaptojanin-homologous region of Salmonella typhimurium SigD is essential for inositol phosphatase activity and Akt activation

FEBS Lett. 2001 Apr 13;494(3):201-7. doi: 10.1016/s0014-5793(01)02356-0.

Abstract

The Ser-Thr kinase Akt is activated in epithelial cells by Salmonella enterica serovar typhimurium. The bacterial effector SigD, which is translocated into host cells via the specialized type III secretion system, is essential for Akt activation. Here, we investigated the inositol phospholipid substrate preferences of SigD. Recombinant SigD preferentially dephosphorylated phosphatidylinositol 3,5-biphosphate and phosphatidylinositol 3,4,5-triphosphate over other phosphatidylinositol lipids. Phosphatidylinositol 3-phosphate was not a substrate, suggesting the 5' phosphate moiety is one of the preferred substrates. Database searches revealed that SigD bears a small region of homology to the mammalian type II inositol 5-phosphatase synaptojanin. Mutation of two conserved residues in this region, Lys527 and Lys530, decreased or abrogated phosphatase activity, respectively. The Shigella flexneri SigD homologue, IpgD, displayed a similar activity in vitro and also activated Akt when used to complement a DeltasigD Salmonella strain. A mutation in IpgD at Lys507, analogous to Lys530 of SigD, also failed to activate Akt. Thus, we have characterized a region near the carboxyl-terminus of SigD which is important for phosphatase activity. We discuss how dephosphorylation of inositol phospholipids by SigD in vivo might contribute to the activation of Akt.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Conserved Sequence / genetics
  • Enzyme Activation
  • Genetic Complementation Test
  • HeLa Cells
  • Humans
  • Lysine / genetics
  • Lysine / metabolism
  • Molecular Sequence Data
  • Mutation / genetics
  • Nerve Tissue Proteins / chemistry*
  • Phosphatidylinositols / metabolism
  • Phosphoric Monoester Hydrolases / chemistry*
  • Phosphoric Monoester Hydrolases / genetics
  • Phosphoric Monoester Hydrolases / metabolism*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Rats
  • Salmonella typhimurium / enzymology*
  • Salmonella typhimurium / genetics
  • Sequence Alignment
  • Shigella flexneri / enzymology
  • Shigella flexneri / genetics
  • Substrate Specificity

Substances

  • Bacterial Proteins
  • Nerve Tissue Proteins
  • Phosphatidylinositols
  • Proto-Oncogene Proteins
  • SopB protein, Bacteria
  • AKT1 protein, human
  • Akt1 protein, rat
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • IpgD protein, Shigella flexneri
  • synaptojanin
  • Phosphoric Monoester Hydrolases
  • myo-inositol-1 (or 4)-monophosphatase
  • SopB protein, Salmonella
  • Lysine