S-layer as versatile building blocks in nanobiotechnology

Many bacteria and archaea possess regularly structured protein lattices, so called S-layers as their outermost cell envelope component which completely cover the cell surface during all stages of bacterial growth and division. In gram-positive bacteria, the S-layer subunits recognize distinct types of heteropolysaccharides, termed secondary cell wall polymers (SCWP) as the proper anchoring structure in the rigid cell wall layer. Basically, two main binding mechanisms between S-layer proteins and SCWPs have been described. The first one, which involves so called S-layer-homologous (SLH) domains and pyruvylated SCWPs has been found to be widespread among prokaryotes and is considered as having been conserved in the course of evolution. The second type of binding mechanism which has been described for Geobacillus stearothermophilus wild-type strains, involves SCWPs that contain 2,3-dideoxy-diacetamido mannosamine uronic acid as the negatively charged component and an N- terminal part which does not possess an SLH-domain. The present study will focus on the investigation of the distribution (occurrence) of a probably second type of conserved binding mechanism between S-layer proteins and SCWPs in selected strains of gram-positive bacteria, as observed between the conserved N-terminus of S-layer proteins from G. stearothermophilus wild-type strains and non pyruvylated, mannosamine uronic acid-containing SCWPs. In this context, also the gene cluster responsible for synthesis of the non pyruvylated SCWP in G. stearothermophilus wild-type strains shall be identified. In the G. stearothermophilus wild-type strain PV72/p6, the S-layer protein SbsA was replaced by the S-layer protein SbsB of the variant designated PV72/p2 under non oxygen-limited growth conditions. During the switch from sbsA to sbsB, also the type of SCWP was changed. In the present project, the DNA region surrounding the S-layer gene sbsB shall be sequenced and investigated for the presence of genes responsible for synthesis of the variant specific, pyruvylated SCWP. Furthermore, it will be investigated, if the genes required for synthesis of the variant specific SCWP are also located on the sbsB-carrying megaplasmid before the switch or if they are located elsewhere on the chromosome in the wild-type strain PV72/p6. In the present study, it will also be studied, if G. stearothermophilus wild-type strains for which the development of SLH-carrying S-layer proteins has not yet been observed, have the intrinsic potential for variant formation under non oxygen-limited growth conditions. Since our group has previously demonstrated that S-layers and SCWPs are useful building blocks for nanobiotechnological applications, the present research project should contribute to a better understanding of the molecular mechanism beyond the highly specific interaction between bacterial S-layer proteins and cell wall polysaccharides.

Many bacteria and archaea possess regularly structured protein lattices, so called S-layers as their outermost cell envelope component which completely cover the cell surface during all stages of bacterial growth and division. In gram-positive bacteria, the S-layer subunits recognize distinct types of heteropolysaccharides, termed secondary cell wall polymers (SCWP) as the proper anchoring structure in the rigid cell wall layer. Basically, two main binding mechanisms between S-layer proteins and SCWPs have been described. The first one, which involves so called S-layer-homologous (SLH) domains and pyruvylated SCWPs has been found to be widespread among prokaryotes and is considered as having been conserved in the course of evolution. The second type of binding mechanism which has been described for Geobacillus stearothermophilus wild-type strains, involves SCWPs that contain 2,3-dideoxy-diacetamido mannosamine uronic acid as the negatively charged component and an N- terminal part which does not possess an SLH-domain. The present study will focus on the investigation of the distribution (occurrence) of a probably second type of conserved binding mechanism between S-layer proteins and SCWPs in selected strains of gram-positive bacteria, as observed between the conserved N-terminus of S-layer proteins from G. stearothermophilus wild-type strains and non pyruvylated, mannosamine uronic acid-containing SCWPs. In this context, also the gene cluster responsible for synthesis of the non pyruvylated SCWP in G. stearothermophilus wild-type strains shall be identified. In the G. stearothermophilus wild-type strain PV72/p6, the S-layer protein SbsA was replaced by the S-layer protein SbsB of the variant designated PV72/p2 under non oxygen-limited growth conditions. During the switch from sbsA to sbsB, also the type of SCWP was changed. In the present project, the DNA region surrounding the S-layer gene sbsB shall be sequenced and investigated for the presence of genes responsible for synthesis of the variant specific, pyruvylated SCWP. Furthermore, it will be investigated, if the genes required for synthesis of the variant specific SCWP are also located on the sbsB-carrying megaplasmid before the switch or if they are located elsewhere on the chromosome in the wild-type strain PV72/p6. In the present study, it will also be studied, if G. stearothermophilus wild-type strains for which the development of SLH-carrying S-layer proteins has not yet been observed, have the intrinsic potential for variant formation under non oxygen-limited growth conditions. Since our group has previously demonstrated that S-layers and SCWPs are useful building blocks for nanobiotechnological applications, the present research project should contribute to a better understanding of the molecular mechanism beyond the highly specific interaction between bacterial S-layer proteins and cell wall polysaccharides.