In a membrane in a more fluid state, Laurdan fluoresces with greater intensity at green wavelengths, with an emission maximum centred at 490 nm, whereas in more ordered regions its emission maximum shifts to the blue wavelengths, centred at 440 nm.
These results demonstrate the utility of a low-cost widefield microscope to effectively replicate results gained from Laurdan staining and two-photon microscopy, in both the heterogeneity of individual cells and protozoan membranes, and in changes in membrane fluidity in response to chemicals that remove the cholesterol from membranes and prevent the cell forming the more ordered regions.
EPR studies of Aβ fibril structure using site-directed spin-labeling demonstrated that this central region is sandwiched between two more highly ordered regions in the fibril structure [58].
Flagellar membranes have also been shown by Tyler et al. [42] to be more highly ordered regions than other regions of the cellular membrane, and this can be seen for the American trypanosome Trypanosoma rangeli, a flagellated protozoon (Fig. 4).
This confirms that negative selection acts to preserve these biochemical types of residues more strongly within ordered regions, as opposed to simply being stronger proportionately over all residues.
It is well-recognized that IDRs typically evolve more rapidly than ordered regions, resulting in greater extents of amino acid substitution [ 30– 32]; however, the forces driving such high substitution rates, specifically the role of positive against negative selection, are not well defined.
Note that posttranslational modifications very commonly occur in disordered regions [ 1], perhaps much more often than in ordered regions, especially those modifications involving phosphorylation [ 21, 22].
The final description of the structure as an ensemble does involve many more (non-independent) parameters than a single description, and particularly needs in essence more parameters to describe poorly ordered regions, which are the least well determined from the data.
The aggregated state may become more ordered where the hydrophobic regions are buried and the polar regions are left exposed to solvent, similar to a micelle formation.
Hence, this loop might become more ordered when the P1′ region of the natural substrate is bound.
