Function
Catalyzes the formation of 6,7-dimethyl-8-ribityllumazine by condensation of 5-amino-6-(D-ribitylamino)uracil with 3,4-dihydroxy-2-butanone 4-phosphate (PubMed:10482294, PubMed:16165152, PubMed:20195542). This is the penultimate step in the biosynthesis of riboflavin. The isozyme RibH2 but not RibH1 is essential for Brucella intracellular survival and replication inside macrophages or in mice (PubMed:20195542). Displays low catalytic activity in comparison with the isozyme RibH1 (PubMed:16165152). Is a highly immunogenic protein (PubMed:14500496). Activates dendritic cells (DCs) in vitro, increasing the levels of costimulatory molecules and the secretion of proinflammatory cytokines, and recruits DCs, B cells and CD8+ T cells in vivo, both effects in a TLR4-dependent manner (PubMed:16455994). Induces the cross presentation of covalently attached peptides and generates a strong and long-lasting humoral immune response without adjuvants; TLR4 signaling is necessary for the induction of the cytotoxic response but not for antigen cross presentation (PubMed:23029192). Elicits a TLR4-mediated protective response against B16 melanoma in mice, slowing tumor growth and prolonging mice survival (PubMed:25973756).