The Immunomodulatory Properties of ß-2,6 Fructans: A Comprehensive Review.

Polysaccharides such as ß-2,1-linked fructans including inulin or fructose oligosaccharides are well-known prebiotics with recognised immunomodulatory properties. In recent years, other fructan types covering ß-2,6-linked fructans, particularly microbial levans, have gained increasing interest in the field. ß-2,6-linked fructans of different degrees of polymerisation can be synthesised by plants or microbes including those that reside in the gastrointestinal tract. Accumulating evidence suggests a role for these ß-2,6 fructans in modulating immune function. Here, we provide an overview of the sources and structures of ß-2,6 fructans from plants and microbes and describe their ability to modulate immune function in vitro and in vivo along with the suggested mechanisms underpinning their immunomodulatory properties. Further, we discuss the limitations and perspectives pertinent to current studies and the potential applications of ß-2,6 fructans including in gut health.

Structural basis for the role of serine-rich repeat proteins from Lactobacillus reuteri in gut microbe-host interactions.

Lactobacillus reuteri, a Gram-positive bacterial species inhabiting the gastrointestinal tract of vertebrates, displays remarkable host adaptation. Previous mutational analyses of rodent strain L. reuteri 100-23C identified a gene encoding a predicted surface-exposed serine-rich repeat protein (SRRP100-23) that was vital for L. reuteri biofilm formation in mice. SRRPs have emerged as an important group of surface proteins on many pathogens, but no structural information is available in commensal bacteria. Here we report the 2.00-Å and 1.92-Å crystal structures of the binding regions (BRs) of SRRP100-23 and SRRP53608 from L. reuteri ATCC 53608, revealing a unique ß-solenoid fold in this important adhesin family. SRRP53608-BR bound to host epithelial cells and DNA at neutral pH and recognized polygalacturonic acid (PGA), rhamnogalacturonan I, or chondroitin sulfate A at acidic pH. Mutagenesis confirmed the role of the BR putative binding site in the interaction of SRRP53608-BR with PGA. Long molecular dynamics simulations showed that SRRP53608-BR undergoes a pH-dependent conformational change. Together, these findings provide mechanistic insights into the role of SRRPs in host-microbe interactions and open avenues of research into the use of biofilm-forming probiotics against clinically important pathogens.