We demonstrate that two photon excited fluorescence and second harmonic generation are sensitive to the hydration, overall β sheet content and molecular orientation of the sample.
Partial conformational change of MPG is associated with formation of a complex with its cargo, and an increase in sheet content occurs upon association with the cell membrane.
Helix and sheet content coincided with an alpha beta structural fold.
The α helical content was 29% for 27 kDa 7B2, while the β sheet content was 14%.
The 21 kDa rat and the 27 kDa C. elegans proteins contained even fewer structural elements, with only 18% α helix and 26% β sheet content.
This was first established for prion diseases and the PK resistance was attributed to the amyloid structure with high beta sheet content of the pathological prion protein [ 15].
Far-UV spectroscopy showed that three of these mutants exhibited similar secondary structure contents as WT CXCL8, whereas two mutants differed significantly: CXCL8 Δ6F17RF21RN71K) displayed less than 50% of the helical and more than 150% of the CXCL8 sheet content, and CXCL8 Δ6F17RF21RE70KN71R) exhibited more than 200% of the helical but similar sheet content compared with CXCL8.
This finding shows that Aβ isoforms are differentially transcytosed or endocytosed through the BBB and that LRP at the BBB favors the clearance of Aβ isoforms relative to high β sheet content.
7 The increase in the β-pleated sheet content of the protein greatly enhances its protease resistance to digestion with proteinase K and hence the nomenclature PrPRes where the Res superscript refers to the resistance to proteinase K mediated degradation.
Regardless, the hallmark feature of the misfolded protein is an induced change in its secondary structure, from a predominantly α-helices containing protein to one with an increase in the β-pleated sheet content.
Structural studies on UbL50P and UbI61T revealed distorted structure with greatly reduced α-helical and elevated β-sheet contents, while UbS20F and UbA46S show mild structural alterations.
