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  • 1.
    Baldassarre, Maurizio
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Li, Chenge
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Eremina, Nadejda
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Goormaghtigh, Erik
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Simultaneous Fitting of Absorption Spectra and Their Second Derivatives for an Improved Analysis of Protein Infrared Spectra2015Inngår i: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 20, nr 7, s. 12599-12622Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Infrared spectroscopy is a powerful tool in protein science due to its sensitivity to changes in secondary structure or conformation. In order to take advantage of the full power of infrared spectroscopy in structural studies of proteins, complex band contours, such as the amide I band, have to be decomposed into their main component bands, a process referred to as curve fitting. In this paper, we report on an improved curve fitting approach in which absorption spectra and second derivative spectra are fitted simultaneously. Our approach, which we name co-fitting, leads to a more reliable modelling of the experimental data because it uses more spectral information than the standard approach of fitting only the absorption spectrum. It also avoids that the fitting routine becomes trapped in local minima. We have tested the proposed approach using infrared absorption spectra of three mixed α/β proteins with different degrees of spectral overlap in the amide I region: ribonuclease A, pyruvate kinase, and aconitase.

  • 2. Kaltofen, Sabine
    et al.
    Li, Chenge
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Huang, Po-Ssu
    Serpell, Louise C.
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    André, Ingemar
    Computational De Novo Design of a Self-Assembling Peptide with Predefined Structure2015Inngår i: Journal of Molecular Biology, ISSN 0022-2836, E-ISSN 1089-8638, Vol. 427, nr 2, s. 550-562Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Protein and peptide self-assembly is a powerful design principle for engineering of new biomolecules. More sophisticated biomaterials could be built if both the structure of the overall assembly and that of the self-assembling building block could be controlled. To approach this problem, we developed a computational design protocol to enable de novo design of self-assembling peptides with predefined structure. The protocol was used to design a peptide building block with a beta alpha beta fold that self-assembles into fibrillar structures. The peptide associates into a double beta-sheet structure with tightly packed a-helices decorating the exterior of the fibrils. Using circular dichroism, Fourier transform infrared spectroscopy, electron microscopy and X-ray fiber diffraction, we demonstrate that the peptide adopts the designed conformation. The results demonstrate that computational protein design can be used to engineer protein and peptide assemblies with predefined three-dimensional structures, which can serve as scaffolds for the development of functional biomaterials. Rationally designed proteins and peptides could also be used to investigate the subtle energetic and entropic tradeoffs in natural self-assembly processes and the relation between assembly structure and assembly mechanism. We demonstrate that the de novo designed peptide self-assembles with a mechanism that is more complicated than expected, in a process where small changes in solution conditions can lead to significant differences in assembly properties and conformation. These results highlight that formation of structured protein/peptide assemblies is often dependent on the formation of weak but highly precise intermolecular interactions.

  • 3.
    Kumar, Saroj
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Li, Chenge
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik. chenge.li@dbb.su.se.
    Montigny, Cedric
    le Maire, Marc
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Conformational changes of recombinant Ca2+-ATPase studied by reaction-induced infrared difference spectroscopy2013Inngår i: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 280, nr 21, s. 5398-5407Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recombinant Ca2+-ATPase was expressed in Saccharomycescerevisiae with a biotin-acceptor domain linked to its C-terminus by a thrombin cleavage site. We obtained 200g of similar to 70% pure recombinant sarcoendoplasmic reticulum Ca2+-ATPase isoform1a (SERCA1a) from a 6-L yeast culture. The catalytic cycle of SERCA1a was followed in real time using rapid scan FTIR spectroscopy. Different intermediate states (Ca(2)E1P and Ca(2)E2P) of the recombinant protein were accumulated using different buffer compositions. The difference spectra of their formation from Ca(2)E1 had the same spectral features as those from the native rabbit SERCA1a. The enzyme-specific activity for the active enzyme fraction in both samples was also similar. The results show that the recombinant protein obtained from the yeast-based expression system has similar structural and dynamic properties as native rabbit SERCA1a. It is now possible to apply this expression system together with IR spectroscopy to the investigation of the role of individual amino acids.

  • 4.
    Li, Chenge
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Infrared spectroscopy: a tool for protein characterization2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Infrared (IR) spectroscopy, which belongs to vibrational spectroscopy, detects the vibrations of molecules, for example, proteins. The absorption of the peptide group gives rise to 9 characteristic bands in the infrared region, named A, B, I-VII, with a decreasing energy or wavenumber (cm-1). Among the 9 bands, amide I, which is mainly caused by C=O stretching vibration, is most sensitive to backbone structure and environment, and therefore can be used for structural analysis. In this thesis, a membrane protein sarcoplasmic reticulum Ca2+-ATPase (SERCA1a) and a self-assembling peptide was studied with IR spectroscopy.  

    In the first two papers, IR spectroscopy was used to assess the quality of a recombinant SERCA1a. A yeast-based expression system was applied to express recombinant SERCA1a, and the reaction cycle as well as the structure was analysed with IR spectroscopy. Different reaction intermediates were accumulated under different buffer conditions upon the release of ATP. The results showed that the recombinant protein shared similar IR features compared to the native protein. However, two SERCA1a preparations showed a difference around 1640 cm-1 in the amide I region. Using curve fitting, the band was assigned to β structure, and further investigation indicated that the difference in this region originates from protein aggregation. In the third paper, a co-fitting approach was tested and showed to be a more reliable method for structural analysis, and it can be applied in the biological IR spectroscopy. In the fourth paper, a peptide was computational designed and was predicted to self-assemble to amyloid fibrils, the formation of the fibril was confirmed with both electron microscopy and X-ray diffraction. IR spectroscopy was used to analyze further the structural details and the results support our structural predication. 

  • 5.
    Li, Chenge
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Kumar, Saroj
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Montigny, Cedric
    le Mairebcd, Marc
    Barth, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för biokemi och biofysik.
    Quality assessment of recombinant proteins by infrared spectroscopy. Characterisation of a protein aggregation related band of the Ca2+-ATPase2014Inngår i: The Analyst, ISSN 0003-2654, E-ISSN 1364-5528, Vol. 139, nr 17, s. 4231-4240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Infrared spectroscopy was used to characterise recombinant sarcoplasmic reticulum Ca2+-ATPase (SERCA1a). In the amide I region, its spectrum differed from that of Ca2+-ATPase prepared from rabbit fast twitch muscle below 1650 cm(-1). A band at 1642 cm(-1) is reduced in the spectrum of the recombinant protein and a band at 1631 cm(-1) is more prominent. By comparison of amide 1 band areas with the known secondary structure content of the protein, we assigned the 1642 cm(-1) band to beta-sheet structure. Further investigation revealed that the 1642 cm(-1) band decreased and the 1631 cm-1 band increased upon storage at room temperature and upon repeated washing of a protein film with water. Also protein aggregates obtained after solubilisation of the rabbit muscle enzyme showed a prominent band at 1631 cm(-1), whereas the spectrum of solubilised ATPase resembled that of the membrane bound protein. The spectral position of the 1631 cm(-1) band is similar to that of a band observed for inclusion bodies of other proteins. The findings show that the absence of the 1642 cm(-1) band and the presence of a prominent band at 1631 cm(-1) indicate protein aggregation and can be used as a quality marker for the optimisation of recombinant protein production. We conclude that recombinant production of SERCA1a, storage at room temperature, repeated washing and aggregation after solubilisation all modify existing beta-sheets in the cytosolic domains so that they become similar to those found in inclusion bodies of other proteins.

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