NYMU Taipei/Protocols2/Properties of TAT Signal Peptides

From 2007.igem.org

• TAT signal peptides consist of three domains
  • The positively charged N-terminal domain (or n-region)
  • The hydrophobic domain (h-rgeion)
    • h-region is typically less hydrophobic than that of Sec-specific signal peptides owing to the presence of more glycine and threonine residues
  • The C-termianl domain (c-region)
• Signal peptides capable of targeting the TAT translocon contain the consensus motif
  • Ser/Thr-Arg-Arg-X-Phe-Leu-Lys (where X is any polar amino acid)
  • File:Tat signal peptides.png
• The TAT signal peptides tend to be longer than their Sec counterparts (primarily because of an extended n-region)
  • Average lengths of 38 a.a for TAT signal peptides and 24 a.a for Sec signal peptides
• The first arginine of the Arg-Arg dipeptide in the consensus motif can be sustituted with Lys and the second arginine can be substituted with Gln or Asn as well as Lys, with varying efficiencies
• The substitution of both arginines with lysines blocks the export of physiological Tat substrate proteins.
• The other residues within the consensus motif are more amenable to amino acid substitutions
  • For example, the Phe and Leu residues can be substituted with other highly hydrophobic amino acids with little effect on export
• The presence of a positive charge in the c-region serves to avoid misdirecting the precursor polypeptide to the Sec translocon.
  • However, many Tat signal peptides lack this charge
• A recent analysis of 29 predicted E. coli Tat signal peptides revealed that Tat selectivity is imparted by the overall charge of the c-region together with the N terminus of the mature protein.