The binding of SDS to proteins at millimolar concentrations of SDS under conditions of pH in which a protein is negatively charged leads to the formation of amyloid fibers. In this paper, we examine whether this is also seen with hyperthermophile-derived proteins, to examine whether low concentrations of SDS can sufficiently structurally perturb these ultra-stable proteins to cause such proteins to also deposit into amyloid fibers. We report that although the range of SDS concentrations over which the phenomenon is seen is somewhat broader for amyloid aggregate formation by hyperthermophile proteins, the phenomenon is essentially the same as reported for mesophile proteins. We have developed our data with multiple hyperthermophile proteins tested into a sophisticated mechanistic understanding of both the effect of low concentrations of SDS on proteins, and the correlation (or lack thereof) with the formation of micelles by SDS. Most significantly, we use the data to demonstrate that amyloid formation is associated with a signature in the circular dichroic spectrum with a band minimum at ~230 nm. Also, we confirm the previous observations with various mesophile proteins that regardless of the nature of secondary structure to begin with, higher concentrations of SDS transform all proteins into helical structures which are presumably long rod-like helices decorated uniformly with SDS. Our data clearly suggests that SDS initially binds to proteins through electrostatic interactions. Subsequently, SDS also interacts through hydrophobic interactions.

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