Probing Structural Changes during Self-assembly of Surface-Active Hydrophobin Proteins that Form Functional Amyloids in Fungi. Issue 20 (12th October 2018)

• Record Type: Journal Article
• Authors: Pham, Chi L.L.; Rodríguez de Francisco, Borja; Valsecchi, Isabel; Dazzoni, Régine; Pillé, Ariane; Lo, Victor; Ball, Sarah R.; Cappai, Roberto; Wien, Frank; Kwan, Ann H.; Guijarro, J. Iñaki; Sunde, Margaret
• Is Part Of: Journal of molecular biology. Volume 430:Issue 20(2018)
• Page Start: 3784
• Page End: 3801
• Publication Date: 2018-10-12
• Subjects: functional amyloid -- hydrophobin -- rodlet -- synchrotron radiation circular dichroism -- Fourier-transform infrared; HHIs hydrophobic/hydrophilic interfaces -- SRCD synchrotron radiation circular dichroism -- FT-IR Fourier-transform infrared spectroscopy -- ThT thioflavin T -- ATR attenuated total reflection; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2018.07.025
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: Hydrophobins are amphiphilic proteins secreted by filamentous fungi in a soluble form, which can self-assemble at hydrophilic/hydrophobic or water/air interfaces to form amphiphilic layers that have multiple biological roles. We have investigated the conformational changes that occur upon self-assembly of six hydrophobins that form functional amyloid fibrils with a rodlet morphology. These hydrophobins are present in the cell wall of spores from different fungal species. From available structures and NMR chemical shifts, we established the secondary structures of the monomeric forms of these proteins and monitored their conformational changes upon amyloid rodlet formation or thermal transitions using synchrotron radiation circular dichroism and Fourier-transform infrared spectroscopy (FT-IR). Thermal transitions were followed by synchrotron radiation circular dichroism in quartz cells that allowed for microbubbles and hence water/air interfaces to form and showed irreversible conformations that differed from the rodlet state for most of the proteins. In contrast, thermal transitions on hermetic calcium fluoride cells showed reversible conformational changes. Heating hydrophobin solutions with a water/air interface on a silicon crystal surface in FT-IR experiments resulted in a gain in β-sheet content typical of amyloid fibrils for all except one protein. Rodlet formation was further confirmed by electron microscopy. FT-IR spectra of pre-formed hydrophobin rodlet preparations also showed a gain in β-sheet characteristic of the amyloid cross-β structure. Our results indicate that hydrophobins are capable of significant conformational plasticity and the nature of the assemblies formed by these surface-active proteins is highly dependent on the interface at which self-assembly takes place. Graphical abstract: Highlights: Class I hydrophobins assemble with conformational change into functional amyloid. Heating of hydrophobins can induce the formation of alternative structures. Conversion to amyloid involves a shift from right-twisted to more relaxed β-structure. Hydrophobin surface activity and plasticity vary with diverse biological functions.