Staphylococcus aureus CapF and related proteins, C-terminal cupin domain
This family contains cupin domains of proteins homologous to Staphylococcus aureus CapF (also known as WbjC in Pseudomonas aeruginosa and FnlB in Escherichia coli). CapF is a bifunctional metalloenzyme produced by certain pathogenic bacteria and is essential in the biosynthetic path of capsular polysaccharide (CP), a mucous layer on the surface of bacterium that facilitates immune evasion and infection. Thus, CapF is an antibacterial/therapeutic target. In S. aureus, enzymes CapE, CapF and CapG catalyze the sequential transformation of UDP-D-GlcNAc in the CP precursor UDP-L-FucNAc via the intermediate compound UDP-N-acetyl-L-talosamine (UDP-L-TalNAc). CapF consists of two domains; the C-terminal cupin domain catalyzes the epimerization of the compound produced by the upstream enzyme CapE, and the N-terminal short-chain dehydrogenase/reductase (SDR) domain catalyzes the reduction of the compound afforded by the cupin domain, requiring one equivalent of NADPH. The cupin domain is crucial for catalyzing the first chemical reaction, and also important for the stability of the enzyme. Similarly, in P. aeruginosa, WbjC, WbjB and WbjD enzymes synthesize UDP-N-acetyl-L-fucosamine, a precursor of the lipopolysacharide component L-fucosamine. The cupin domains contain a conserved "jelly roll-like" beta-barrel fold.
Jiyao W et al.(2023). "The conserved domain database in 2023.",