Biophysical properties of human body louse nit related proteins: LNSP1, Agp9 and Agp22.

The human parasitic head and body lice lay their eggs on either hair or clothing. Attachments of the eggs are possible because the female lice secret a glue substance from the accessory gland along with the egg, which hardens into a nit sheath that secures and protects the egg (The "nit" commonly refers to either the louse egg with an embryo or the empty hatched egg). Proteins called the louse nit sheath protein (LNSP) are suggested to be the major proteins of the nit sheath, but transcriptome profiling of the accessory glands indicated other proteins such as Agp9 and Agp22 are also expressed in the glands. In this study, human body louse LNSP1 (partial), Agp9, and Agp22 are recombinantly produced using the E. coli expression system, and the biophysical properties characterized. Circular dichroism analysis indicated that the secondary structure elements of LNSP1 N-terminal and middle-domains, Agp9, and Agp22 are prominently random coiled with up to 10-30% anti-parallel ß-sheet element present. Size-exclusion chromatography profiles of LNSP1 proteins further suggested that the ß-sheets made of the smaller N-terminal domain stacks onto the ß-sheets of the larger middle-domain.

The structure of Deinococcus radiodurans transcriptional regulator HucR retold with the urate bound.

HucR is a MarR family protein of Deinococcus radiodurans, which binds tightly to the intergenic region of HucR and the uricase gene to inhibit their expression. Urate (or uric acid) antagonizes the repressor function of HucR by binding to HucR to impede its association with the cognate DNA. The previously reported crystal structure of HucR was without the bound urate showing significant structural homology to other MarR structures. In this paper, we report the crystal structure of HucR determined with the urate bound. However, despite the fact that the urate is found at a site well-known to harbor ligands in other MarR family proteins, the overall HucR structure indicates that no significant change in structure takes place with the urate bound. Structure analysis further suggests that the urate interaction in HucR is mediated by histidine/glutamate side chains and ordered water molecules stabilized by various residues. Such interaction is quite unique compared to other known structural interactions between urate and its binding proteins. Furthermore, structural comparison of the apo- and the urate bound forms allows us to hypothesize that the Trp20-mediated water network in the apo-form stabilizes the proper HucR fold for cognate DNA binding, and that urate binding, also via Trp20, and the consequent reorganization of water molecules in the binding pocket, likely disrupts the DNA binding configuration to result in the attenuated DNA binding.