A reliable reducing end assay for chito-oligosaccharides

Molecular basis for peptidoglycan recognition by a bactericidal lectin

RegIII proteins are secreted C-type lectins that kill Gram-positive bacteria and play a vital role in antimicrobial protection of the mammalian gut. RegIII proteins bind their bacterial targets via interactions with cell wall peptidoglycan but lack the canonical sequences that support calcium-dependent carbohydrate binding in other C-type lectins. Here, we use NMR spectroscopy to determine the molecular basis for peptidoglycan recognition by HIP/PAP, a human RegIII lectin. We show that HIP/PAP recognizes the peptidoglycan carbohydrate backbone in a calcium-independent manner via a conserved "EPN" motif that is critical for bacterial killing. While EPN sequences govern calcium-dependent carbohydrate recognition in other C-type lectins, the unusual location and calcium-independent functionality of the HIP/PAP EPN motif suggest that this sequence is a versatile functional module that can support both calcium-dependent and calcium-independent carbohydrate binding. Further, we show HIP/PAP binding affinity for carbohydrate ligands depends on carbohydrate chain length, supporting a binding model in which HIP/PAP molecules "bind and jump" along the extended polysaccharide chains of peptidoglycan, reducing dissociation rates and increasing binding affinity. We propose that dynamic recognition of highly clustered carbohydrate epitopes in native peptidoglycan is an essential mechanism governing high-affinity interactions between HIP/PAP and the bacterial cell wall.

Enzyme, protein, carbohydrate, and phenolic contaminants in commercial tyrosinase preparations: potential problems affecting tyrosinase activity and inhibition studies

Commercial mushroom tyrosinase contains other proteins, enzymes, carbohydrates, and phenolic material besides tyrosinase. Carbohydrate and phenolic material comprise a large percentage of the powder resuspensions derived from Agaricus bisporus. Enzyme assays identified the presence of tyrosinase, laccase, beta-glucosidase, beta-galactosidase, beta-xylosidase, cellulase, chitinase, xylanase, and mannanase in the commercial tyrosinase. Protein sequencing indicated the presence of tyrosinase, a lectin, and a putative mannanase as well as 10 unidentified protein/peptides in the commercial tyrosinase preparations. Characteristics of tyrosinase isoforms were similar in two different commercial tyrosinase sources. Inhibition studies indicated that I 50 values for some tyrosinase inhibitors were different when the crude powder was compared to a partially purified tyrosinase. The presence of these contaminants has the potential to affect studies using commercial tyrosinase.