Search results for "protein structure"
showing 10 items of 757 documents
Structure of the anchor-domain of myristoylated and non-myristoylated HIV-1 Nef protein 1 1Edited by A. R. Fersht
1999
Negative factor (Nef) is a regulatory myristoylated protein of human immunodeficiency virus (HIV) that has a two-domain structure consisting of an anchor domain and a core domain separated by a specific cleavage site of the HIV proteases. For structural analysis, the HIV-1 Nef anchor domain (residues 2-57) was synthesized with a myristoylated and non-myristoylated N terminus. The structures of the two peptides were studied by1H NMR spectroscopy and a structural model was obtained by restrained molecular dynamic simulations. The non-myristoylated peptide does not have a unique, compactly folded structure but occurs in a relatively extended conformation. The only rather well-defined canonical…
Folding in vitro of light-harvesting chlorophyll a/b protein is coupled with pigment binding.
2002
The major light-harvesting chlorophyll a/b protein (LHCIIb) of the plant photosynthetic apparatus is able to self-organise in vitro. When the recombinant apoprotein, Lhcb1, is solubilised in the denaturing detergent sodium (or lithium) dodecylsulfate (SDS or LDS) and then mixed with chlorophylls and carotenoids under renaturing conditions, structurally authentic LHCIIb forms. Assembly of functional LHCIIb, as indicated by the establishment of energy transfer between complex-bound chlorophyll molecules, occurs in two apparent kinetic steps with time constants of 10 to 30 seconds and 50 to 300 seconds, depending on the reaction conditions. Here, we use circular dichroism (CD) in the far-UV ra…
Consecutive binding of chlorophylls a and b during the assembly in vitro of light-harvesting chlorophyll-a/b protein (LHCIIb).
2006
The apoprotein of the major light-harvesting chlorophyll a/b complex (LHCIIb) is post-translationally imported into the chloroplast, where membrane insertion, protein folding, and pigment binding take place. The sequence and molecular mechanism of the latter steps is largely unknown. The complex spontaneously self-organises in vitro to form structurally authentic LHCIIb upon reconstituting the unfolded recombinant protein with the pigments chlorophyll a, b, and carotenoids in detergent micelles. Former measurements of LHCIIb assembly had revealed two apparent kinetic phases, a faster one (tau1) in the range of 10 s to 1 min, and a slower one (tau2) in the range of several min. To unravel th…
Random mutations directed to transmembrane and loop domains of the light-harvesting chlorophyll a/b protein: impact on pigment binding.
1999
The major light-harvesting complex of photosystem II (LHCII) can be reconstituted in vitro by folding its bacterially expressed apoprotein, Lhcb, in detergent solution in the presence of chlorophylls and carotenoids. To compare the impact of alpha-helical transmembrane domains and hydrophilic loop domains of the apoprotein on complex formation and stability, we introduced random mutations into a segment of the protein comprising the stromal loop, the third (C-proximal) transmembrane helix, and part of the amphipathic helix in the C-terminal domain. The mutant versions of Lhcb were screened for the loss of their ability to form stable LHCII upon reconstitution in vitro. Most steps during the…
Rigid versus Flexible Protein Matrix: Light-Harvesting Complex II Exhibits a Temperature-Dependent Phonon Spectral Density
2018
Dynamics-function correlations are usually inferred when molecular mobility and protein function are simultaneously impaired at characteristic temperatures or hydration levels. In this sense, excitation energy transfer in the photosynthetic light-harvesting complex II (LHC II) is an untypical example because it remains fully functional even at cryogenic temperatures relying mainly on interactions of electronic states with protein vibrations. Here, we study the vibrational and conformational protein dynamics of monomeric and trimeric LHC II from spinach using inelastic neutron scattering (INS) in the temperature range of 20-305 K. INS spectra of trimeric LHC II reveal a distinct vibrational …
Pigment Binding, Fluorescence Properties, and Oligomerization Behavior of Lhca5, a Novel Light-harvesting Protein
2005
A new potential light-harvesting protein, named Lhca5, was recently detected in higher plants. Because of the low amount of Lhca5 in thylakoid membranes, the isolation of a native Lhca5 pigment-protein complex has not been achieved to date. Therefore, we used in vitro reconstitution to analyze whether Lhca5 binds pigments and is actually an additional light-harvesting protein. By this approach we could demonstrate that Lhca5 binds pigments in a unique stoichiometry. Analyses of pigment requirements for light-harvesting complex formation by Lhca5 revealed that chlorophyll b is the only indispensable pigment. Fluorescence measurements showed that ligated chlorophylls and carotenoids are arran…
Water-Soluble Chlorophyll Protein (WSCP) Stably Binds Two or Four Chlorophylls
2017
Water-soluble chlorophyll proteins (WSCPs) of class IIa from Brassicaceae form tetrameric complexes containing one chlorophyll (Chl) per apoprotein but no carotenoids. The complexes are remarkably stable toward dissociation and protein denaturation even at 100 °C and extreme pH values, and the Chls are partially protected against photooxidation. There are several hypotheses that explain the biological role of WSCPs, one of them proposing that they function as a scavenger of Chls set free upon plant senescence or pathogen attack. The biochemical properties of WSCP described in this paper are consistent with the protein acting as an efficient and flexible Chl scavenger. At limiting Chl concen…
Early folding events during light harvesting complex II assembly in vitro monitored by pulsed electron paramagnetic resonance
2016
Efficient energy transfer in the major light harvesting complex II (LHCII) of green plants is facilitated by the precise alignment of pigments due to the protein matrix they are bound to. Much is known about the import of the LHCII apoprotein into the chloroplast via the TOC/TIC system and its targeting to the thylakoid membrane but information is sparse about when and where the pigments are bound and how this is coordinated with protein folding. In vitro, the LHCII apoprotein spontaneously folds and binds its pigments if the detergent-solubilized protein is combined with a mixture of chlorophylls a and b and carotenoids. In the present work, we employed this approach to study apoprotein fo…
Derivation of coarse-grained simulation models of chlorophyll molecules in lipid bilayers for applications in light harvesting systems
2015
The correct interplay of interactions between protein, pigment and lipid molecules is highly relevant for our understanding of the association behavior of the light harvesting complex (LHCII) of green plants. To cover the relevant time and length scales in this multicomponent system, a multi-scale simulation ansatz is employed that subsequently uses a classical all atomistic (AA) model to derive a suitable coarse grained (CG) model which can be backmapped into the AA resolution, aiming for a seamless conversion between two scales. Such an approach requires a faithful description of not only the protein and lipid components, but also the interaction functions for the indispensable pigment mo…
Amino acids in the second transmembrane helix of the Lhca4 subunit are important for formation of stable heterodimeric light-harvesting complex LHCI-…
2007
Photosynthetic light-harvesting complexes (LHCs) are assembled from apoproteins (Lhc proteins) and non-covalently attached pigments. Despite a considerable amino acid sequence identity, these proteins differ in their oligomerization behavior. To identify the amino acid residues determining the heterodimerization of Lhca1 and Lhca4 to form LHCI-730, we mutated the poorly conserved second transmembrane helix of the two subunits. Mutated genes were expressed in Escherichia coli and the resultant proteins were refolded in vitro and subsequently analyzed by gel electrophoresis. Replacement of the entire second helix in Lhca4 by the one of Lhca3 abolished heterodimerization, whereas it had no eff…