Spider silk is protein fibers with extraordinary mechanical properties. Up to now, it is still poorly understood how silk proteins are kept in a soluble form before spinning into fibers and how the protein molecules are aligned orderly to form fibers. Minor ampullate spidroin is one of the seven types of silk proteins, which consists of four types of domains: N-terminal domain, C-terminal domain (CTD), repetitive domain (RP) and linker domain (LK). Here we report the tertiary structure of CTD and secondary structures of RP and LK in aqueous solution, and their roles in protein stability, solubility and fiber formation. The stability and solubility of individual domains are dramatically different and can be explained by their distinct structures. For the tri-domain miniature fibroin, RP-LK-CTDMi, the three domains have no or weak interactions with one another at low protein concentrations (<1 mg/ml). The CTD in RP-LK-CTDMi is very stable and soluble, but it cannot stabilize the entire protein against chemical and thermal denaturation while it can keep the entire tri-domain in a highly water-soluble state. In the presence of shear force, protein aggregation is greatly accelerated and the aggregation rate is determined by the stability of folded domains and solubility of the disordered domains. Only the tri-domain RP-LK-CTDMi could form silk-like fibers, indicating that all three domains play distinct roles in fiber formation: LK as a nucleation site for assembly of protein molecules, RP for assistance of the assembly and CTD for regulating alignment of the assembled molecules.

The hydroxyl radical, •OH, is one of the most reactive free radicals and plays significant roles in the oxidative degradation of organic pollutants and the electron transfer of inorganic ions in natural and engineered environmental processes. To quantitatively determine the contribution of •OH to oxidative reactions, a specific scavenger, such as tert-butyl alcohol (TBA), is usually added to eliminate •OH effects. Although TBA is commonly assumed to transform •OH into oxidatively inert products, this study demonstrates that utilizing TBA as an •OH scavenger generates the secondary peroxyl radical (ROO•), influencing the oxidation of transition metals, such as Mn. Although ROO• is less reactive than •OH, it has an extended half-life and a longer diffusion distance that enables more redox reactions, such as the oxidation of Mn2+(aq) to MnIV oxide solids. In addition to promoting Mn2+(aq) oxidation kinetics, TBA can also affect the crystalline phases, oxidation states, and morphologies of Mn oxide solids. Thus, the oxidative roles of •OH in aqueous redox reactions cannot be examined simply by adding TBA: the effects of secondary ROO• must also be considered. This study urges a closer look at the potential formation of secondary radicals during scavenged oxidative reactions in environmental systems.

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Halide ions are naturally abundant in oceans and estuaries. Large amounts of highly saline efflux are also generated and discharged to surface water from desalination processes and from unconventional oil...