Biomedical subjects

Clair Baldock

Publications and source records attributed to Clair Baldock.

6 recordsLinked to original sources

PubMed2003

Fibrillin microfibrils are stiff reinforcing fibres in compliant tissues.

Fibrillin-rich microfibrils have endowed tissues with elasticity throughout multicellular evolution. We have used molecular combing techniques to determine Young's modulus for individual microfibrils and X-ray diffraction of zonular filaments of the eye to establish the linearity of microfibril periodic extension. Microfibril periodicity is not altered at physiological zonular tissue extensions and Young's modulus is between 78 MPa and 96 MPa, which is two orders of magnitude stiffer than elastin. We conclude that elasticity in microfibril-containing tissues arises primarily from reversible alterations in supra-microfibrillar arrangements rather than from intrinsic elastic properties of individual microfibrils which, instead, act as reinforcing fibres in fibrous composite tissues.

Aged↗

PubMed2003

Raman microscopy and X-ray diffraction, a combined study of fibrillin-rich microfibrillar elasticity.

Fibrillin-rich microfibrils are essential elastic structures contained within the extracellular matrix of a wide variety of connective tissues. Microfibrils are characterized as beaded filamentous structures with a variable axial periodicity (average 56 nm in the untensioned state); however, the basis of their elasticity remains unknown. This study used a combination of small angle x-ray scattering and Raman microscopy to investigate further the packing of microfibrils within the intact tissue and to determine the role of molecular reorganization in the elasticity of these microfibrils. The application of relatively small strains produced no overall change in either molecular or macromolecular microfibrillar structure. In contrast, the application of larger tissue extensions (up to 150%) resulted in a markedly different structure, as observed by both Raman microscopy and small angle x-ray scattering. These changes occurred at different levels of architecture and are interpreted as ranging from alterations in peptide bond conformation to domain rearrangement. This study demonstrates the importance of molecular elasticity in the mechanical properties of fibrillin-rich microfibrils in the intact tissue.

Animals↗

PubMed2003

The supramolecular organization of collagen VI microfibrils.

Collagen VI has a ubiquitous distribution throughout connective tissues, and has key roles in linking cells and matrix macromolecules. We have generated three-dimensional reconstructions of collagen VI microfibrils using automated electron tomography (AET) in order to obtain new insights into the organisation of collagen VI in assembled microfibrils. Analysis of the reconstruction data has allowed the resolution of the double-beaded structure into smaller subunits. Volume calculations from the tomography data indicate that ten and six A-domains could be packed into the N and C-terminal regions from each monomer, respectively. A putative location for the globular N-terminal regions of the alpha3 chain, important for microfibril assembly and function, has been identified. Some surfaces of the alpha3 chain N-terminal domains appear to be exposed on the surface of a microfibril, where they may provide an interactive surface for molecules. Analysis of the interbead region provides evidence for complex triple helical supercoiling in microfibrils. Frequently, two strands were visualised emerging from the beaded region and merging into a single interbead region. Measurements taken from the AET data show that there is a decrease in periodicity from dimer/tetramer to microfibrils. Molecular combing reverses this effect by mechanically increasing periodicity to give measurements similar to the component dimers/tetramers. Together, these data have provided important new insights into the organisation and function of these large macromolecular assemblies.

Animals↗

PubMed2002

Fibrillin: from microfibril assembly to biomechanical function.

Fibrillins form the structural framework of a unique and essential class of extracellular microfibrils that endow dynamic connective tissues with long-range elasticity. Their biological importance is emphasized by the linkage of fibrillin mutations to Marfan syndrome and related connective tissue disorders, which are associated with severe cardiovascular, ocular and skeletal defects. These microfibrils have a complex ultrastructure and it has proved a major challenge both to define their structural organization and to relate it to their biological function. However, new approaches have at last begun to reveal important insights into their molecular assembly, structural organization and biomechanical properties. This paper describes the current understanding of the molecular assembly of fibrillin molecules, the alignment of fibrillin molecules within microfibrils and the unique elastomeric properties of microfibrils.

Animals↗

PubMed2002

Crystallization and preliminary X-ray crystallographic studies on acyl-(acyl carrier protein) from Escherichia coli.

Acyl carrier proteins carry the lipid substrate to the enzymes of the fatty acid synthase system. Crystals of Escherichia coli acyl carrier protein to which a butyryl group has been attached via a thioester link to the phosphopantetheine prosthetic arm have been obtained by the hanging-drop vapour-diffusion method. These crystals belong to space group P2(1)2(1)2(1), with unit-cell parameters a = 27.6, b = 41.6, c = 63.7 A. The asymmetric unit appears to contain one subunit, corresponding to a packing density of 2.1 A(3) Da(-1). Crystals of the selenomethionine-substituted (SeMet) protein were obtained using different conditions and belong to space group P6(3), with unit-cell parameters a = b = 63.4, c = 37.0 A, alpha = beta = 90, gamma = 120 degrees and with a monomer in the asymmetric unit (V(M) = 2.5 A(3) Da(-1)). Crystals of a SeMet butyryl-ACP I62M variant were obtained using the conditions for the native protein. Like the native crystals, these belong to space group P2(1)2(1)2(1) and have unit-cell parameters a = 27.3, b = 41.9, c = 64.5 A. A data set suitable for MAD phasing was collected from the crystals of the I62M variant to 1.8 A resolution on the ESRF beamline ID14-4.

Acyl Carrier Protein↗

PubMed2002

X-ray crystallographic studies on butyryl-ACP reveal flexibility of the structure around a putative acyl chain binding site.

Acyl carrier protein (ACP) is an essential cofactor in biosynthesis of fatty acids and many other reactions that require acyl transfer steps. We have determined the first crystal structures of an acylated form of ACP from E. coli, that of butyryl-ACP. Our analysis of the molecular surface of ACP reveals a plastic hydrophobic cavity in the vicinity of the phosphopantethylated Ser36 residue that is expanded and occupied by the butyryl and beta-mercaptoethylamine moieties of the acylated 4'-phosphopantetheine group in one of our crystal forms. In the other form, the cavity is contracted, and we propose that the protein has adopted the conformation after delivery of substrate into the active site of a partner enzyme.

Acyl Carrier Protein↗