Pro- and eukaryotic surface display systems. A: phage display, e.g. phage M13. pIII: minor capsid protein, pVIII: major capsid protein [19]. B: gram negative bacteria, e.g. E. coli. Anchor protein: OmpA, CM: cytoplasma membrane, OM: outer membrane, PP: periplasma, PG: peptidoglycan [20]. C: gram positive bacteria, e.g. Staphylococcus sp. Anchor protein: SpA: S. aureus protein A [21]. D: yeast, direct display, e.g. S. cerevisiae. Anchor protein: Agα: agglutinin α. CW: cell wall [22]. E: yeast, indirect display. Aga: agglutinin a: dimeric protein, Aga1 and Aga2, connected by disulfide bonds. Aga1 acts as surface anchor, while the target protein is fused to Aga2 [23]. F: baculovirus (right) and insect cells (left). Anchor protein: major coat protein gp64, which is present on virions and infected insect cells [24].