The OmpA signal peptide is a 21-amino acid sequence that targets fused proteins to the Sec secretion pathway in E. coli. It can be used to increase protein yield and simplify purification procedures. 

Here are some things to know about the OmpA signal peptide:

• Secretion
  The OmpA signal peptide directs the secretion of fused proteins into the periplasmic space. The fused protein is not folded until it is secreted. 
• Cleavage
  After secretion, the signal peptidase cleaves the signal peptide after residue 21. The recognition sequence for this cleavage is Ala-X-Ala. 
• Optimizing signal peptides
  The optimal signal peptide for a particular protein must be determined experimentally. 
• Comparison to other signal peptides
  The type of signal peptide can affect the expression level and structure of the N-terminus of recombinant proteins. For example, when the N-terminal sequence of a protein is not critical, the OmpA signal peptide is preferred.