Structural studies on flagellins from shape and antigenic variants of Salmonella and Proteus flagella
The primary structures of flagellins from antigenic and shape variants of Salmonella and Proteus flagella were studied. H antigenic differences in Salmonella are related to differences in amino acid composition of the flagellin molecules: peptide differences were observed between thermolytic, and between chymotryptic peptide maps of Salmonella g.... antigenic flagellins. These differences were located on the CNBr A fragments of the flagellins. Homologous CNBr A fragments were almost as effective as homologous flagella as inhibitors of antiserum raised against g.... antigenic flagella, as measured by immobilisation-inhibition and complement fixation-inhibition assays. Thus the H antigenic determinants appear to be located primarily on the CNBr A fragment, although some results suggest that they might extend onto the CNBr B fragment in certain flagellins. The sites of amino acid substitutions in morphological mutants of Salmonella g... antigenic flagellins appear to be located at either the N-terminal (CNBr B) or C-terminal (CNBr C and CNBr D) regions of the flagellin molecule. The C-terminus of the molecule is conserved. Several epsilon-N-methyllysine residues were detected in most of the Salmonella g.... antigenic flagellins analysed and, in fewer numbers, in certain P. morganii flagellins. The absence of E-N-methyllysine residues in flagellins of diverse bacteria was noted. Arginine and tyrosine residues of various bacterial flagellins were differentiated by chemical modification into three groups: residues not accessible to modification; residues accessible in the monomer but not in the polymer; residues which are modified in both the monomer and polymer. Residues belonging to the second group may be implicated in the self-assembly of flagellin subunits into flagellar filaments. Comparison of amino acid sequences of bacterial flagellins indicated sequences of homology at the N- and C-terminal regions of the flagellin molecule. These regions may be essential for the assembly of subunits into functional filaments. The central part of the molecule, however, appears to be a variable region which is exposed in the polymer and predominantly bears the H-antigenic characteristics of the bacterium.