Partial characterization of a peptidoglycan-protein complex from Fusobacterium nucleatum Fev1

A protein in the cell wall of Fusobacterium nucleatum Fev1 remained associated with the peptidoglycan during extraction with various detergents and organic solvents. On digestion of this peptidoglycan-protein complex (PPC) with murein hydrolases, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed polypeptide bands with apparent molecular weights (MWs) in the range of 3000 to 40,000. After reaction with maleic anhydride the electrophoretic mobilities of these polypeptide bands increased to those of MWs 3000 to 12,000. The PPC protein showed a limited susceptibility toward trypsin, giving polypeptides that migrated in SDS-PAGE as a diffuse band with MW in the range of 3000 to 6000. The amino acid composition of all polypeptide bands eluted from SDS-PAGE was very similar, whichever enzyme was used for the solubilization of the PPC, and was nearly identical to that found for the protein moiety of the PPC. On the basis of a MW of 3000 for a protein unit, about one molecule of protein was found per five peptidoglycan subunits. Lanthionine was not found associated with released polypeptide, and muramic acid and glucosamine were either absent or present in amounts less than one molecule per protein unit. The PPC was immunogenic in rabbits, and purified anti-PPC IgG reacted with murein hydrolase-released protein separated on SDS-PAGE but preferentially with bands of MWs greater than 18,000.