NYMU Taipei/Protocols2/Properties of TAT Signal Peptides

<ul>
    <li>TAT signal peptides consist of three domains
    <ul>
        <li>The positively charged N-terminal domain (or n-region)</li>
        <li>The hydrophobic domain (h-rgeion)
        <ul>
            <li>h-region is typically less hydrophobic than that of Sec-specific signal peptides owing to the presence of more glycine and threonine residues</li>
        </ul>
        </li>
        <li>The C-termianl domain (c-region)</li>
    </ul>
    </li>
    <li>Signal peptides capable of targeting the TAT translocon contain the consensus motif
    <ul>
        <li>Ser/Thr-Arg-Arg-X-Phe-Leu-Lys (where X is any polar amino acid)</li>
        <li>[[image:Tat_signal_peptides.png]]</li>
    </ul>
    </li>
    <li>The TAT signal peptides tend to be longer than their Sec counterparts (primarily because of an extended n-region)
    <ul>
        <li>Average lengths of 38 a.a for TAT signal peptides and 24 a.a for Sec signal peptides</li>
    </ul>
    </li>
    <li>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</li>
    <li>The substitution of both arginines with lysines blocks the export of physiological Tat substrate proteins.</li>
    <li>The other residues within the consensus motif are more amenable to amino acid substitutions
    <ul>
        <li>For example, the Phe and Leu residues can be substituted with other highly hydrophobic amino acids with little effect on export</li>
    </ul>
    </li>
    <li>The presence of a positive charge in the c-region serves to avoid misdirecting the precursor polypeptide to the Sec translocon.
    <ul>
        <li>However, many Tat signal peptides lack this charge</li>
    </ul>
    </li>
    <li>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.</li>
</ul>