Spider major ampullate silk (MA) is natures’ toughest fibre. There is thus immense interest among scientists across different fields in the attainment of an understanding about why and how spiders produce such amazing fibres. Accordingly there are now many publications on MA silk genetic expression patterns, secondary and tertiary protein structures, silk fibre physical and engineering properties, and silk spinning technologies aimed at emulating natural and synthetic processes.
There has, nevertheless, not been any study to date that has united the disciplines, and systematically show how genetic expressions influence the chemistry and structures of silk proteins (spidroin), with consequences on fibre properties. Our latest study in PloS One (https://doi.org/10.1371/journal. pone.0192005) has, nevertheless, gone a long way to rectifying this problem.
Our study, which involved collaborators from Australia (UNSW) and Taiwan (Tunghai University and National Synchrotron Radiation Research Centre), assessed MA silk genetic expression patterns, silk amino acid compositions, spidroin structural variations, and mechanical properties of the spun fibres, in five species of Australian Araneoid spider that were placed on nutrient enhanced or nutrient devoid diets. We subsequently used a multitude of approaches from Fluidigm RT-PCR technologies, to High Performance Liquid Chromatography, to Small and Wide Angle X-ray Scattering (SAXS/WAXS), to tensile performance testing to assess the silk properties at multiple (i.e. nano to macro) scales.
Interestingly, the consequences of the different nutrient environments on silk mechanics varied across the five species, meaning that MA silk changes in property to different degrees across spiders species when under nutrient deprivation. The primary driver of mechanical property variability in most instances seemed to be differential genetic expression, which caused alterations to the amino acid compositions of the silk, resulting in shifts in the protein’s secondary structures and, predominantly, a predictable shift in silk mechanics. For instance, we consistently found that proline composition was associated with silk amorphous region structural changes and this subsequently affected silk extensibility.
Nevertheless, when no significant changes to protein structures occurred, any shifts in genetic expressions or silk amino acid compositions did not result in any shifts in silk mechanics. Indeed, significant shifts in the genetic expression in redback spider silks were found, but these did not correlate with any shifts in protein structure or silk mechanics.
Our study is the first to systematically assess how genetic expressions influence spidroin structures, and the resultant consequences on spider silk fibre properties. Our study thus provides insights into silk property variability at multiple scales. We expect it to inspire renewed efforts to produce new synthetic MA silk-like fibres; an outcome which continues to elude bioengineers.