TY - JOUR A1 - Hofmann, Hagen A1 - Soranno, Andrea A1 - Borgia, Alessandro A1 - Gast, Klaus A1 - Nettels, Daniel A1 - Schuler, Benjamin T1 - Polymer scaling laws of unfolded and intrinsically disordered proteins quantified with single-molecule spectroscopy JF - Proceedings of the National Academy of Sciences of the United States of America N2 - The dimensions of unfolded and intrinsically disordered proteins are highly dependent on their amino acid composition and solution conditions, especially salt and denaturant concentration. However, the quantitative implications of this behavior have remained unclear, largely because the effective theta-state, the central reference point for the underlying polymer collapse transition, has eluded experimental determination. Here, we used single-molecule fluorescence spectroscopy and two-focus correlation spectroscopy to determine the theta points for six different proteins. While the scaling exponents of all proteins converge to 0.62 +/- 0.03 at high denaturant concentrations, as expected for a polymer in good solvent, the scaling regime in water strongly depends on sequence composition. The resulting average scaling exponent of 0.46 +/- 0.05 for the four foldable protein sequences in our study suggests that the aqueous cellular milieu is close to effective theta conditions for unfolded proteins. In contrast, two intrinsically disordered proteins do not reach the T-point under any of our solvent conditions, which may reflect the optimization of their expanded state for the interactions with cellular partners. Sequence analyses based on our results imply that foldable sequences with more compact unfolded states are a more recent result of protein evolution. KW - protein folding KW - single-molecule FRET KW - coil-globule transition KW - polymer theory Y1 - 2012 U6 - https://doi.org/10.1073/pnas.1207719109 SN - 0027-8424 VL - 109 IS - 40 SP - 16155 EP - 16160 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Bremer, Anne A1 - Wolff, Martin A1 - Thalhammer, Anja A1 - Hincha, Dirk K. T1 - Folding of intrinsically disordered plant LEA proteins is driven by glycerol-induced crowding and the presence of membranes JF - The FEBS journal N2 - Late embryogenesis abundant (LEA) proteins are related to cellular dehydration tolerance. Most LEA proteins are predicted to have no stable secondary structure in solution, i.e., to be intrinsically disordered proteins (IDPs), but they may acquire alpha-helical structure upon drying. In the model plant Arabidopsis thaliana, the LEA proteins COR15A and COR15B are highly induced upon cold treatment and are necessary for the plants to attain full freezing tolerance. Freezing leads to increased intracellular crowding due to dehydration by extracellular ice crystals. In vitro, crowding by high glycerol concentrations induced partial folding of COR15 proteins. Here, we have extended these investigations to two related proteins, LEA11 and LEA25. LEA25 is much longer than LEA11 and COR15A, but shares a conserved central sequence domain with the other two proteins. We have created two truncated versions of LEA25 (2H and 4H) to elucidate the structural and functional significance of this domain. Light scattering and CD spectroscopy showed that all five proteins were largely unstructured and monomeric in dilute solution. They folded in the presence of increasing concentrations of trifluoroethanol and glycerol. Additional folding was observed in the presence of glycerol and membranes. Fourier transform infra red spectroscopy revealed an interaction of the LEA proteins with membranes in the dry state leading to a depression in the gel to liquid-crystalline phase transition temperature. Liposome stability assays revealed a cryoprotective function of the proteins. The C- and N-terminal extensions of LEA25 were important in cryoprotection, as the central domain itself (2H, 4H) only provided a low level of protection. KW - intrinsically disordered proteins KW - late embryogenesis abundant proteins KW - osmolytes KW - protein folding KW - protein-membrane interaction Y1 - 2017 U6 - https://doi.org/10.1111/febs.14023 SN - 1742-464X SN - 1742-4658 VL - 284 SP - 919 EP - 936 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Hornemann, Andrea A1 - Eichert, Diane Madeleine A1 - Hoehl, Arne A1 - Tiersch, Brigitte A1 - Ulm, Gerhard A1 - Ryadnov, Maxim G. A1 - Beckhoff, Burkhard T1 - Investigating Membrane-Mediated Antimicrobial Peptide Interactions with Synchrotron Radiation Far-Infrared Spectroscopy JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - Synchrotron radiation-based Fourier transform infrared spectroscopy enables access to vibrational information from mid over far infrared to even terahertz domains. This information may prove critical for the elucidation of fundamental bio-molecular phenomena including folding-mediated innate host defence mechanisms. Antimicrobial peptides (AMPs) represent one of such phenomena. These are major effector molecules of the innate immune system, which favour attack on microbial membranes. AMPs recognise and bind to the membranes whereupon they assemble into pores or channels destabilising the membranes leading to cell death. However, specific molecular interactions responsible for antimicrobial activities have yet to be fully understood. Herein we probe such interactions by assessing molecular specific variations in the near-THz 400-40 cm(-1) range for defined helical AMP templates in reconstituted phospholipid membranes. In particular, we show that a temperature-dependent spectroscopic analysis, supported by 2D correlative tools, provides direct evidence for the membrane-induced and folding-mediated activity of AMPs. The far-FTIR study offers a direct and information-rich probe of membrane-related antimicrobial interactions. KW - antimicrobial peptides KW - electrostatic interactions KW - IR spectroscopy KW - phospholipid membranes KW - protein folding Y1 - 2022 U6 - https://doi.org/10.1002/cphc.202100815 SN - 1439-4235 SN - 1439-7641 VL - 23 IS - 4 PB - Wiley-VCH CY - Weinheim ER -