Cell Surface Display

The manipulation of the cell surfaces of prokaryotes (mainly bacteria) and eukaryotes (such as Yeast) has manifested to be an area of stupendous ongoing research, with intelligent widespread applications spanning different arenas of biological sciences (Charbit et al., 1988; Cruz et al., 2000; Francisco et al., 1993; Götz, 1990; Jostock & Dübel, 2005; Keskinkan et al., 2004; Kotrba et al., 1999; Lee & Schnaitman, 1980; Liljeqvist et al., 1997; Martineau et al., 1991; Mizuno et al., 1983; Sousa et al., 1996; Taschner et al., 2002; Wernérus & Ståhl, 2004; Willett et al., 1995; Xu & Lee, 1999). Till date, majority of the surface display systems developed for Gram-negative bacteria involve introducing external peptides into surface-approachable loops of naturally displayed proteins. This sometimes put extreme size restrictions on the displayed components (Wernérus & Ståhl, 2004). However, this problem is more or less resolved since larger proteins could be inserted through some recently developed bacterial display systems for Gram-negative bacteria (Charbit et al., 1988; Cruz et al., 2000; Lee & Schnaitman, 1980; Mizuno et al., 1983; Xu & Lee, 1999). Thanks to some tireless research, it is now evident that the structural properties of the cell wall in Gram-positive bacteria, i.e. the thick peptidoglycan layer, make them suitable candidates for strict laboratory procedures and demanding field applications (Jostock & Dübel, 2005). On the other hand, lower transformation efficiency has been a significant disadvantage of using Gram-positive bacteria (Wernérus & Ståhl, 2004), considering if someone is working with surface-displayed conjunctional libraries for affinity-based selections. However, libraries of significant size could also be obtained for Gram-positive bacteria. Transformation frequencies as high as 105 − 106 colony forming units/μg of DNA have been observed for Staphylococcus carnosus (Götz, 1990). Until recently, different surface displaying systems have been successfully developed (Lee et al., 2003). Based on their recombinant portfolios, these can be categorized into three principal groups: C-terminal fusion, N-terminal fusion, and Sandwich fusion. Natural occurring surface proteins with distinct restricting signals within their N-terminal part may use a C-terminal fusion mechanism to affix external peptides to the C terminus of that functional portion. In a similar way, a N-terminal fusion system points external proteins to the cell wall by using either Staphylococcus aureus protein A, fibronectin binding protein B, Streptococcus pyogenes fibrillar M protein, and Saccharomyces cerevisiae α-agglutinin, all of which contain C-terminal screening signals. However, in many surface proteins, the whole structure is an essentiality for successful aggregation, primarily because the anchoring regions are absent in their subunits (such as outer membrane proteins or OMPs). Here, the sandwich fusion plays a vital role. Escherichia coli PhoE, FimH, FliC, and PapA act as good carriers for sandwich fusion for small peptides (Xu & Lee, 1999). 4