To identify the linkage of the Kdo residues, methylation analysis of the K1 hydrophobic moiety was performed using the Ciucanu and Kerek method with modifications to preserve the linkages of Neu Ac and Kdo (25-methyl-octitol were observed (ratio of 1:1.38), suggestive of an alternating polymer of 2,4- and 2,7-linked Kdo (Fig. A small amount of terminal Kdo was also detected, indicative of some hydrolysis in the sample.The presence of characteristic fragment ions in electron-impact MS confirmed the assignment of 4-, 7-, and terminal Kdo species, and chemical-ionization MS confirmed that all molecular ions were consistent with monolinked Kdo.The charge of the ion is shown next to the letter identifying it.( K1 sample confirmed the presence of C16:0 fatty acids, glycerol, Kdo, and Neu Ac.This lipid has been implicated in anchoring CPSs to the outer membrane (16).
The composition of the acyl chain is in parentheses and the number of Kdo and Neu Ac residues in each ion is indicated.
One common virulence factor is the capsule, which consists of long-chain capsular polysaccharides (CPSs) anchored in the outer membrane.
CPSs are often important for preventing phagocytosis and complement-mediated killing and thus represent an attractive therapeutic target (1, 2).
Capsules protect pathogens from host defenses including complement-mediated killing and phagocytosis and therefore represent a major virulence factor.
Capsular polysaccharides are synthesized by enzymes located in the inner (cytoplasmic) membrane and are then translocated to the cell surface.