1. Cell Surface Targeting

2. Two routes Protein-protein interfaceDNA-DNA interface

3. Protein-protein

4. Protein domain BioBricks 5’ GTTTCTCCGAATTCGCGGCCGCTTCTAGAG EcoRI XbaI TACTAGTAGCGGCCGCTGCAGGGAGAAAC 3’ SpeI PstI Standard part 5’ GTTTCTCCGAATTCGCGGCCGCTTCTAGA EcoRI XbaI ACTAGTAGCGGCCGCTGCAGGGAGAAAC 3’ SpeI PstI Protein domain 5’ GTTTCTCCGAATTCGCGGCCGCTTCTAGA EcoRI XbaI ACTAGTAGCGGCCGCTGCAGGGAGAAAC 3’ SpeI PstI Domain assembly ACTAGA ThrArg Mixed

5. Streptavidin Found in bacteria Streptomyces avidinii Full-length ~160 aa’s, core ~ 140 aa’s Binds strongly to biotin (vitamin H or B7) –K d ~ 10 -15 M (Chaiet, 1964) No cysteines, no carbohydrates, no charge McDevitt, 1999

6. Lpp-OmpA surface expression Lipoprotein (Lpp): major outer membrane protein (most abundant protein in E. coli by numbers); targeted to outer membrane Outer membrane protein A (OmpA): well-characterized eight-strand beta-barrel transmembrane domain; stable surface xpression Lpp 20aa signal peptide + Lpp aa 1-9 + OmpA aa 46-159 + surface protein OmpA 46-66 also successful Bla, Fv fragments, OPH, Cex (C. fimi) Goal: Use Lpp-OmpA to express streptavidin on the surface to bind biotinylated DNA or protein to the membrane Francisco et al., 1992

7. Progress/agenda Created BioBricks of three streptavidin clones from Ting lab: wild-type, wild-type + His6 tag, dead mutant Created BioBricks of full Lpp and OmpA, then Lpp(1-29), OmpA(46-66), OmpA(46-159) More BioBricks: single-chain dimer streptavidin from Aslan lab Assembly and expression of Lpp-OmpA-streptavidin

8. DNA-DNA

9. Aptamers Short DNA/RNA sequences that have high specificity and affinity for substrate Low generation time

10. Pros –Potential control of binding kinetics and thermodynamics –Control of relative amounts of different substrates that bind cell surface –Swappable Cons –Interaction strength limited by strength of aptamer- protein interactions

11. First designs

12. Progress Have begun to characterize DNA-DNA interaction Gel shift assays have failed to prove that aptamers are binding the proteins For the future: more promising assays.