**Abbreviations**


*Inhibition of Protein Fibrillation by Hydrogen Sulfide DOI: http://dx.doi.org/10.5772/intechopen.86221*

*Amyloid Diseases*

bonds in HEWL remains intact during the fibrillation of HEWL in control solution, as we have described here. It has been suggested that a partial denaturation of lysozyme precedes fibril formation because the native tertiary structure would not allow rearrangement to the cross-β sheet structure due to steric constraints [8, 76]. It has also been reported that partial denaturation, the first step of lysozyme fibrillation, is an irreversible process [46]. At the same time, a fully denatured lysozyme forms amorphous aggregates that prevent fibril formation [64]. It is believed that the fully denatured protein lacks the hydrophobic side chains present in partially unordered intermediates. In addition, amorphous aggregates potentially decrease the effective concentration of HEWL available for fibril formation [64]. In agreement with these observations, our results suggest that lysozyme denatures strongly in the presence of H2S and forms unordered aggregates that prevent β-sheet formation and fibrillation. Regarding this, it has been shown that Hb under physiological conditions and in presence of 45% 2,2,2-trifluoethanol (TFE) produces amyloid-like fibril species [28]. The mechanism surrounding these fibril events remains almost unknown. Curiously, myoglobin and hemoglobin do not have any S-S moiety in their chemical structures, and **Figures 5** and **6** show that the fibrillation inhibition effect of H2S depends on its concentration. Specifically, the Mb and Hb α-helix assemblies are almost preserved at higher H2S concentrations. Therefore, in these hemeproteins, it is not clear the inhibition mechanism by H2S, since CD indicates that hydrogen sulfide prevents β-sheet formation and fibrillation without altering significantly the α-helical structure of Mb or Hb. Also similar to HEWL, the addition of H2S to Mb or Hb fibrils does not revert the β-sheet amyloid fibrils to the native α-structure. These results are consistent with the ThT findings that β-sheets are present in Mb and Hb amyloid-like fibrils in the presence of 45% TFE and that increasing concentration of H2S inhibits β-sheet formation. The findings demonstrate the same H2S effect on to the fibrillation of Mb monomer and Hb tetramer, although some quantitative

kinetic differences may be evident and need further study.

This work was supported in part by the National Science Foundation under Award CHE-1152752 (I.K.L.), NSF PREM: Wisconsin-Puerto Rico Partnership for Research and Education in Materials under Award DMR-0934115 (J.L.G), the National Institute of Health-INBRE PR under Award P20GM103475-13 (J.L.G.), the Alfred P. Sloan NACME Grant No. 2010-3-02, and BioXFEL-National Science

**Acknowledgements**

**Abbreviations**

Foundation Grant No. 1231306.

H2S hydrogen sulfide HEWL hen egg white lysozyme

ThT thioflavin T cys cysteine

DUVRR deep ultraviolet resonance Raman

AFM atomic force microscopy

SOD super oxide dismutase hGH human growth hormone DPDS dipropyl disulfide DPTS dipropyl trisulfide DTT dithiothreitol

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