{Reference Type}: Journal Article {Title}: Two remarkable serine/leucine polymorphisms in Helicobacter pylori: functional importance for serine protease HtrA and adhesin BabA. {Author}: Backert S;Tegtmeyer N;Horn AHC;Sticht H;Linz B; {Journal}: Cell Commun Signal {Volume}: 22 {Issue}: 1 {Year}: 2024 May 2 {Factor}: 7.525 {DOI}: 10.1186/s12964-024-01635-5 {Abstract}: Single nucleotide polymorphisms (SNPs) account for significant genomic variability in microbes, including the highly diverse gastric pathogen Helicobacter pylori. However, data on the effects of specific SNPs in pathogen-host interactions are scarce. Recent functional studies unravelled how a serine/leucine polymorphism in serine protease HtrA affects the formation of proteolytically active trimers and modulates cleavage of host cell-to-cell junction proteins during infection. A similar serine/leucine mutation in the carbohydrate binding domain of the adhesin BabA controls binding of ABO blood group antigens, enabling binding of either only the short Lewis b/H antigens of blood group O or also the larger antigens of blood groups A and B. Here we summarize the functional importance of these two remarkable bacterial SNPs and their effect on the outcome of pathogen-host interactions.