Variation of gonococcal lipooligosaccharide structure is due to alterations in poly-G tracts in lgt genes encoding glycosyl transferases.

Abstract

SUlTlnlaryThe lipooligosaccharide (LOS) expressed by gonococci spontaneously varies its structure at high frequency, but the underlying genetic mechanism has not been described. We have previously reported that the genes encoding the glycosyl transferases responsible for the biosynthesis of the variable o~ chain of the LOS of Neisseria gonorrhoeae are located in a locus containing five genes, lgtA, lgtB, IgtC, IgtD, and lgtE. Sequence analysis showed that tgtA, lgtC, and IgtD contained poly-G tracts within the coding frames, leading to the hypothesis that shiftsin the number of guanosine residues in the poly-G tracts might be responsible for the.high frequency variation in structure of gonococcal LOS. We now provide experimental evidence confirming this hypothesis.

Phase variation in tcpH modulates expression of the ToxR regulon in Vibrio cholerae

“…In Neisseria gonorrhoeae, phase variation of expression of outer membrane protein II occurs by a change in the number of CTCTT tandemly repeated sequences, producing a frameshift within the signal peptide of the gene encoding this protein; this provides a translational control mechanism for phase variation in the expression of individual outer membrane protein II alleles (Murphy et al, 1989). Different strains of N. gonorrhoeae also express a variety of related lipo-oligosaccharide structures on their cell surface, and phase variation in lipo-oligosaccharide types relates to changes in the number of guanine residues in polyguanine tracts within individual open reading frames involved in the synthesis of different lipo-oligosaccharide structures (Yang and Gotschlich, 1996;Burch et al, 1997). In N. meningitidis, unencapsulated variants arise by deletion of one C residue within a string of seven C residues in the open reading frame of siaD, which encodes an enzyme involved in the synthesis of the polysialic acid capsule of this organism (Hammerschmidt et al, 1996).…”

Phase variable changes in genes lgtA and lgtC within the lgtABCDE operon of Neisseria gonorrhoeae can modulate gonococcal susceptibility to normal human serum

“…The lgtABCDE operon, originally described by Gotschlich, 21 encodes enzymes responsible for extension of the LOS a-chain, and three of the genes (lgtA, lgtC and lgtD) contain homopolymeric G nucleotide tracts that are subject to phase-variable expression. Single nucleotide deletions or insertions in these genes due to slipped-strand mispairing events can place these genes in or out of frame, 8,21 resulting in variable production of full-length and functional enzymes. We now report that phase-variable expression of two genes within the lgtABCDE operon (lgtA and lgtC) can significantly impact the susceptibility of gonococci to the bacteriolytic action of NHS.…”

Genetic diversity of three lgt loci for biosynthesis of lipooligosaccharide (LOS) in Neisseria species The GenBank accession numbers for the sequences reported in this paper are AF470655–AF470685.

“…However, N. meningitidis LOS is heterogeneous and its expression is subject to antigenic variation (Burch et al, 1997 ;Danaher et al, 1995 ;Jennings et al, 1995 ;Yang & Gotschlich, 1996), which complicate the LOS phenotype as a marker for epidemiological purposes. On the basis of genetic organization of the three lgt loci, 25 N. meningitidis strains examined in this study can be divided into 10 LOS genotypes (Table 4).…”

“…1) (Banerjee et al, 1998). Four genes at the lgt-1 and lgt-3 loci, lgtA, lgtC, lgtD and lgtG, have a homopolymeric tract that is thought to be involved in LOS phase variation by the slipped strand mispairing mechanism (Danaher et al, 1995 ;Jennings et al, 1995 ;Yang & Gotschlich, 1996). Therefore, both the composition and expression of lgt will regulate the biosynthesis of LOS.…”

“…1). The Neisseria LOS is heterogeneous and the expression of LOS is subject to phase variation (Burch et al, 1997 ;Danaher et al, 1995 ;Jennings et al, 1995 ;Yang & Gotschlich, 1996). N. meningitidis LOS is divided into 12 immunotypes (L1-12) on the basis of specific antibody reactions Zollinger et al, 1977Zollinger et al, , 1980.…”