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 β-sheet element present. Size-exclusion chromatography profiles of LNSP1 proteins further suggested that the β-sheets made of the smaller N-terminal domain stacks onto the β-sheets of the larger middle-domain.