1. Protein and toxin export and secretion
Final localization of proteins
- Cell membrane ~ 300 distinct proteins
- Periplasm (Gram(-)) ~ 100 proteins
-External membrane (Gram(-)) ~ 50 proteins
- Extracellular proteins
- Toxins (patogens)
Export – translocation across the membrane
Secretion – translocation to the exterior of the cell
Questions:
- What determines a protein final location?
-What energy source drives translocation?
-How a perotein knows its final location?

2. General secretory pathway, GSP
Components of the Sec system:
1) Signal peptide
2) A chaperone
3) A membranar translocase
The signal peptide has 3 distinct regions:
Basic region, positively charged at neutral pH
central hidrophobic region, to interact with the membrane;
C-terminal region containing a sequence recognized by a peptidase.

4. The sec and TAT transport systems

6. Protein secretion At least 6 protein secretion systems in bacteria
- Types I and III – sec-independent
-Types II and IV – sec-dependent