Phase variation in H type I and Lewis a epitopes of Helicobacter pylori lipopolysaccharide

Helicobacter pylori NCTC 11637 lipopolysaccharide (LPS) expresses the human blood group antigens Lewis x (Le(x)), Le(y), and H type I. In this report, we demonstrate that the H type I epitope displays high-frequency phase var iation. One variant expressed Le(x) and Le(y) and no H type I as determined by serology; this switch was reversible. Insertional mutagenesis in NCTC 1 1637 of JHP563 (a poly(C) tract containing an open reading frame homologous to glycosyltransferases) yielded a transformant with a serotype similar to the phase variant. Structural analysis of the NCTC 11637 LPS confirmed the loss of the H type T epitope, Sequencing of JHP563 in strains NCTC 11637, an H type I-negative variant, and an H type I-positive switchback variant s howed a C14 (gene on), C13 (gene off), and C14 tract, respectively. Inactiv ation of strain G27, which expresses Le(x), Le(y), H type I, and Le(a), yie lded a transformant that expressed Le(x) and Le(y), We conclude that JHP563 encodes a beta 3-gaclactosyltransferase involved in the biosynthesis of H type I and Le(a) and that phase variation in H type I is due to C-tract cha nges in this gene. A second H type I-negative variant (variant 3a) expresse d Le(x) and Le(a) and had lost both H type I and Le(y) expression. Inactiva tion of HP093-HP094 resulted in a transformant expressing Le(x) and lacking Le(y) and H type I. Structural analysis of a mutant LPS confirmed the sero logical data. We conclude that the HP093-HP094 alpha 2-fucosyltransferase ( alpha 2-FucT) gene product is involved in the biosynthesis of both Le(y) an d Le(x). Finally, we inactivated HP0379 in strain 3a, The transformant had lost both Le(x) and Le(a) expression, which demonstrates that the HP0379 ge ne product is both an alpha 3- and an alpha 4-FucT, Our data provide unders tanding at the molecular level of how H. pylori is able to diversify in the host, a requirement likely essential for successful colonization and trans mission.