Signal Peptide Structure
The core of the signal peptide contains a long stretch of hydrophobic amino acids that has a tendency to form a single alpha-helix. In addition, many signal peptides begin with a short positively charged stretch of amino acids, which may help to enforce proper topology of the polypeptide during translocation by what is known as the positive-inside rule. At the end of the signal peptide there is typically a stretch of amino acids that is recognized and cleaved by signal peptidase. However this cleavage site is absent from transmembrane-domains that serve as signal peptides, which are sometimes referred to as signal anchor sequences. Signal peptidase may cleave during, or after completion of, translocation to generate a free signal peptide and a mature protein. The free signal peptides are then digested by specific proteases.
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