Biochemistry And Assembly Of The Regular Surface Array Of Aquaspirillum Serpens Mw5

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Kist, Marion Leah
Biology; Microbiology
thesis / dissertation description
The regularly-structured surface array of the Gram-negative bacterium, Aquaspirillum serpens MW5, consists of two layers of hexagonally-arranged subunits which, together, produce a complex and linear surface pattern. The components of the structure were isolated and identified as proteins and the biochemical and in vitro assembly properties of these proteins were examined.;The array was removed from cell envelopes and dissociated by treatment with 6 M urea. The isolated surface components reassembled onto outer membrane and self-assembled into planar sheets in vitro. Both assemblies required the presence of calcium or strontium. Image analysis of the self-assembled sheets showed that they were highly similar to the in vivo structure.;The two layers were removed sequentially from cell envelopes; initial treatment with pH 10.3 buffer removed the outermost surface layer while subsequent treatment with 6 M urea removed the innermost layer. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed that the outer and inner layers of the array were composed of proteins with molecular weights of 125,000 (125K) and 150,000 (150K), respectively.;The two layers assembled sequentially; the 150K protein formed an array, either alone by self-assembly, or on an outer membrane surface, and the 125K protein required that array as a template for its in vitro assembly.;The amino acid compositions of the two proteins were similar. They demonstrated a number of properties in common with other bacterial RS proteins including a high proportion of acidic and hydrophobic residues.;The relatedness of the two RS proteins of strain MW5 was examined as well as their relatedness to the RS protein of A. serpens VHA. The three proteins were immunologically cross-reactive; peptide mapping, however, demonstrated differences between them. The sequence differences detected supported the observed biochemical and assembly differences between the RS proteins.;The surface array of A. serpens MW5 provides an excellent model for the assembly of a complex macromolecular structure. The biochemical and in vitro assembly properties of the components of this array, examined in this study, provides a basis for the study of the in vivo assembly of the structure.