Crystal and molecular structure of a collagen-like peptide at 1.9 A resolution.
ABSTRACT The structure of a protein triple helix has been determined at 1.9 angstrom resolution by x-ray crystallographic studies of a collagen-like peptide containing a single substitution of the consensus sequence. This peptide adopts a triple-helical structure that confirms the basic features determined from fiber diffraction studies on collagen: supercoiling of polyproline II helices and interchain hydrogen bonding that follows the model II of Rich and Crick. In addition, the structure provides new information concerning the nature of this protein fold. Each triple helix is surrounded by a cylinder of hydration, with an extensive hydrogen bonding network between water molecules and peptide acceptor groups. Hydroxyproline residues have a critical role in this water network. The interaxial spacing of triple helices in the crystal is similar to that in collagen fibrils, and the water networks linking adjacent triple helices in the crystal structure are likely to be present in connective tissues. The breaking of the repeating (X-Y-Gly)n pattern by a Gly-->Ala substitution results in a subtle alteration of the conformation, with a local untwisting of the triple helix. At the substitution site, direct interchain hydrogen bonds are replaced with interstitial water bridges between the peptide groups. Similar conformational changes may occur in Gly-->X mutated collagens responsible for the diseases osteogenesis imperfecta, chondrodysplasias, and Ehlers-Danlos syndrome IV.
SourceAvailable from: Fatma BrikiActa Crystallographica Section A Foundations of Crystallography 08/2011; 67(a1):C264-C265. DOI:10.1107/S0108767311093391 · 2.07 Impact Factor
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ABSTRACT: In this work we describe the self-assembly of a collagen-like periodic mini-fibril from a recombinant triple helix. The triple helix, designated Col108, is expressed in E. coli using an artificial gene and consists of a 378-residue triple helix domain organized into three pseudo-repeating sequence units. The peptide forms a stable triple helix with a melting temperature of 41 °C. Upon increases of pH and temperature, Col108 self-assembles in solution into smooth mini-fibrils with the cross-striated banding pattern typical of fibrillar collagens. The banding pattern is characterized by an axially repeating feature of ~ 35 nm as observed by TEM and AFM. Both the negatively stained and the positively stained TEM patterns of the Col108 mini-fibrils are consistent with a staggered arrangement of triple helices having a staggering value of 123 residues, a value closely connected to the size of one repeat sequence unit. A mechanism is proposed for the mini-fibril formation of Col108 in which the axial periodicity is instigated by the built-in sequence periodicity and stabilized by the optimized interactions between the triple helices in a 1-unit staggered arrangement. Lacking hydroxyproline residues and telopeptides - two factors implicated in the fibrillogenesis of native collagen - the Col108 mini-fibrils demonstrate that sequence features of the triple helical domain alone are sufficient to 'code' for axially repeating periodicity of fibrils. To our knowledge, Col108 is the first designed triple helix to self-assemble into periodic fibrils, and offers a unique opportunity to unravel the specific molecular interactions of collagen fibrillogenesis. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.Journal of Biological Chemistry 02/2015; 290(14). DOI:10.1074/jbc.M113.542241 · 4.60 Impact Factor
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ABSTRACT: Solid-state NMR spectroscopy has had a major impact on our understanding of the structure of mineralized tissues, in particular bone. Bone exemplifies the organic-inorganic composite structure inherent in mineralized tissues. The organic component of the extracellular matrix in bone is primarily composed of ordered fibrils of collagen triple-helical molecules, in which the inorganic component, calcium phosphate particles, composed of stacks of mineral platelets, are arranged around the fibrils. This perspective argues that key factors in our current structural model of bone mineral have come about through NMR spectroscopy and have yielded the primary information on how the mineral particles interface and bind with the underlying organic matrix. The structure of collagen within the organic matrix of bone or any other structural tissue has yet to be determined, but here too, this perspective shows there has been real progress made through application of solid-state NMR spectroscopy in conjunction with other techniques. In particular, NMR spectroscopy has highlighted the fact that even within these structural proteins, there is considerable dynamics, which suggests that one should be cautious when using inherently static structural models, such as those arising from X-ray diffraction analyses, to gain insight into molecular roles. It is clear that the NMR approach is still in its infancy in this area, and that we can expect many more developments in the future, particularly in understanding the molecular mechanisms of bone diseases and ageing. Copyright © 2015 Elsevier Inc. All rights reserved.Journal of Magnetic Resonance 04/2015; 253. DOI:10.1016/j.jmr.2014.12.011 · 2.32 Impact Factor