Bacterial Derived Carbohydrates Bind Cyr1 and Trigger Hyphal Growth in Candida albicans.

The dimorphic yeast Candida albicans is the most common pathogenic fungus found in humans. While this species is normally commensal, a morphological switch from budding yeast to filamentous hyphae allows the fungi to invade epithelial cells and cause infections. The phenotypic change is controlled by the adenylyl cyclase, Cyr1. Interestingly, this protein contains a leucine-rich repeat (LRR) domain, which is commonly found in innate immune receptors from plants and animals. A functional and pure LRR domain was obtained in high yields from E. coli expression. Utilizing a surface plasmon resonance assay, the LRR was found to bind diverse bacterial derived carbohydrates with high affinity. This domain is capable of binding fragments of peptidoglycan, a carbohydrate polymer component of the bacterial cell wall, as well as anthracyclines produced by Streptomyces, leading to hyphae formation. These findings add another dimension to the human microbiome, taking into account yeast-bacteria interactions that occur in the host.

Crohn's Disease Variants of Nod2 Are Stabilized by the Critical Contact Region of Hsp70.

Nod2 is a cytosolic, innate immune receptor responsible for binding to bacterial cell wall fragments such as muramyl dipeptide (MDP). Upon binding, subsequent downstream activation of the NF-κB pathway leads to an immune response. Nod2 mutations are correlated with an increased susceptibility to Crohn's disease (CD) and ultimately result in a misregulated immune response. Previous work had demonstrated that Nod2 interacts with and is stabilized by the molecular chaperone Hsp70. In this work, it is shown using purified protein and in vitro biochemical assays that the critical Nod2 CD mutations (G908R, R702W, and 1007fs) preserve the ability to bind bacterial ligands. A limited proteolysis assay and luciferase reporter assay reveal regions of Hsp70 that are capable of stabilizing Nod2 and rescuing CD mutant activity. A minimal 71-amino acid subset of Hsp70 that stabilizes the CD-associated variants of Nod2 and restores a proper immune response upon activation with MDP was identified. This work suggests that CD-associated Nod2 variants could be stabilized in vivo with a molecular chaperone.

The effect of NOD2 on the microbiota in Crohn's disease.

Recent advancements toward the treatment of Crohn's disease (CD) indicate great promise for long-term remission. CD patients suffer from a complex host of dysregulated interactions between their innate immune system and microbiome. The most predominant link to the onset of CD is a genetic mutation in the innate immune receptor nucleotide-binding oligomerization domain-containing 2 (NOD2). NOD2 responds to the presence of bacteria and stimulates the immune response. Mutations to NOD2 promote low diversity and dysbiosis in the microbiome, leading to impaired mucosal barrier function. Current treatments suppress the immune response rather than enhancing the function of this critical protein. New progress toward stabilizing NOD2 signaling through its interactions with chaperone proteins holds potential in the development of novel CD therapeutics.