Thermally induced permutations of antigenicity and conformation of arachin (peanut globular protein)*.

The reactivity of arachin (principal storage protein of the peanut) with anti-arachin decreased after arachin was heated at certain temperatures. Infrared and circular dichroic spectra of heated and unheated samples of arachin were examined to determine whether conformational modes changed concomitantly with decreased antigenicity. Infrared absorbances of each sample at amide I, II and V bands were essentially identical; however, absorbances at amide IV and VI bands were altered in relative intensities proportionally to the temperatures of treatment. Conformational modes, determined by circular dichroism, gradually increased in content of unordered structure from x-helical and pleated sheet modes relative to the temperature of treatment. These observations are discussed in regard to relationships of the loss of antigenicity to conformatonal changes in heated arachin.     

Extracellular chloride signals collagen IV network assembly during basement membrane formation

Basement membranes are defining features of the cellular microenvironment; however, little is known regarding their assembly outside cells. We report that extracellular Cl⁻ ions signal the assembly of collagen IV networks outside cells by triggering a conformational switch within collagen IV noncollagenous 1 (NC1) domains. Depletion of Cl⁻ in cell culture perturbed collagen IV networks, disrupted matrix architecture, and repositioned basement membrane proteins. Phylogenetic evidence indicates this conformational switch is a fundamental mechanism of collagen IV network assembly throughout Metazoa. Using recombinant triple helical protomers, we prove that NC1 domains direct both protomer and network assembly and show in Drosophila that NC1 architecture is critical for incorporation into basement membranes. These discoveries provide an atomic-level understanding of the dynamic interactions between extracellular Cl⁻ and collagen IV assembly outside cells, a critical step in the assembly and organization of basement membranes that enable tissue architecture and function. Moreover, this provides a mechanistic framework for understanding the molecular pathobiology of NC1 domains.