Aspects of X-ray diffraction on single spider fibers.

A complete image of the helical arrangement of cellulose fibrils in the S2 layer of adjacent wood cells of Picea abies (Norwegian spruce) was obtained by applying position-resolved synchrotron X-ray microdiffraction on cells in cross section. In contrast to conventional fiber diffraction studies, the incident beam was parallel to the longitudinal cell axis, resulting in a glancing angle μ far from 90° with respect to the cellulose fibrils. This special choice of diffraction geometry allowed us to take advantage of an asymmetry effect in the two-dimensional diffraction patterns arising from the curvature of the Ewald sphere to obtain information on the local orientation of the cellulose fibrils. The small size of the beam, smaller than the thickness of a single cell wall, allowed mesh scans over intact transverse sections of adjacent wood cells with a microscopic position resolution. The scan yielded a map of diffraction patterns that could readily serve as a microscopic image. Each of the diffraction patterns was then used to evaluate the local orientation of the cellulose fibrils at the actual beam position. The combination of these results gave an image of cellulose fibrils forming (Z) helices in several adjacent wood cells.

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Imaging of the helical arrangement of cellulose fibrils in wood by synchrotron X-ray microdiffraction

Structure–property relation in poly(p-phenylene terephthalamide) (PPTA) fibers

Focused X-ray beams from third generation synchrotron sources allow the possibility of data collection from previously unusable protein microcrystals of only a few microns in size.

Small is beautiful: protein micro-crystallography

Silks are highly expressed, secreted proteins that represent a substantial metabolic cost to the insects and spiders that produce them. Female spiders in the superfamily Araneoidea (the orb-spinning spiders and their close relatives) spin six different kinds of silk (three fibroins and three fibrous protein glues) that differ in amino acid content and protein structure. In addition to this diversity in silks produced by different glands, we found that individual spiders of the same species can spin dragline silks (drawn from the spider's ampullate gland) that vary in content as well. Freely foraging ARGIOPE: argentata (Araneae: Araneoidea), collected from 13 Caribbean islands, produced dragline silk that showed an inverse relationship between the amount of serine and glycine they contained. X-ray microdiffraction of the silks localized these differences to the amorphous regions of the protein that are thought to lend silks their elasticity. The crystalline regions of the proteins, which lend silks their strength, were unaffected. Laboratory experiments with ARGIOPE: keyserlingi suggested that variation in silk composition reflects the type of prey the spiders were fed but not the total amount of prey they received. Hence, it may be that the amino acid content (and perhaps the mechanical properties) of dragline silk spun by ARGIOPE: directly reflect the spiders' diet. The ability to vary silk composition and, possibly, function is particularly important for organisms that disperse broadly, such as Argiope, and that occupy diverse habitats with diverse populations of prey.

/pdf/evidence-for-diet-effects-on-the-composition-of-silk-4ww5ai24l4.pdf

Evidence for Diet Effects on the Composition of Silk Proteins Produced by Spiders

It is shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fibers with a 2 μm synchrotron radiation beam in a few seconds per pattern. Preferred orientation was obs...

K. Wagner

Papers

Microdiffraction Experiments on Single Polymeric Fibers by Synchrotron Radiation