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At least 163 records · Page 9Linked to original sources
PubMed1998

Neurofilament-L homopolymers are less mechanically stable than native neurofilaments.

Neurofilaments are cytoskeletal components of neurones that are thought to play an important structural role in the axon. Specific functions of neurofilaments are not yet well defined; however, other intermediate filaments are known to have structural and mechanical functions in different cell types. The atomic force microscope (AFM) can be used to visualize and manipulate biological structures through direct physical contact. This allows the AFM to be used to probe the mechanical properties of these structures. In this paper we present AFM images of native neurofilaments isolated from bovine spinal cord, composed of NF-L, NF-M and NF-H, and filaments polymerized in vitro from purified NF-L. Morphologically these structures, in solution and under ambient conditions, are in agreement with previous data from electron microscopy. However, repeated scanning of NF-L homopolymers (in solution) produced significant disruptions of segments of filaments, both within and at the ends of the filaments. This disruption resulted in complete loss of portions of the filaments and in breaks in the continuity of the filaments. Repeated scanning of isolated native neurofilaments under similar conditions produced no detectable structural changes. Under extremely high applied forces the native neurofilaments were bent and distorted by the action of the AFM tip, but were never broken. These data suggest that purified NF-L is not sufficient to confer complete mechanical stability to neurofilaments.

Animals↗
PubMed1998

Neurofilament-L homopolymers are less mechanically stable than native neurofilaments.

Neurofilaments are cytoskeletal components of neurones that are thought to play an important structural role in the axon. Specific functions of neurofilaments are not yet well defined; however, other intermediate filaments are known to have structural and mechanical functions in different cell types. The atomic force microscope (AFM) can be used to visualize and manipulate biological structures through direct physical contact. This allows the AFM to be used to probe the mechanical properties of these structures. In this paper we present AFM images of native neurofilaments isolated from bovine spinal cord, composed of NF-L, NF-M and NF-H, and filaments polymerized in vitro from purified NF-L. Morphologically these structures, in solution and under ambient conditions, are in agreement with previous data from electron microscopy. However, repeated scanning of NF-L homopolymers (in solution) produced significant disruptions of segments of filaments, both within and at the ends of the filaments. This disruption resulted in complete loss of portions of the filaments and in breaks in the continuity of the filaments. Repeated scanning of isolated native neurofilaments under similar conditions produced no detectable structural changes. Under extremely high applied forces the native neurofilaments were bent and distorted by the action of the AFM tip, but were never broken. These data suggest that purified NF-L is not sufficient to confer complete mechanical stability to neurofilaments.

Journal Article↗
PubMed1990

The effect of the L-azetidine-2-carboxylic acid residue on protein conformation. II. Homopolymers and copolymers.

The alteration of polymer conformational properties caused by the replacement of L-proline by L-azetidine-2-carboxylic acid (Aze) has been studied by means of conformational energy computations. In addition to poly(Aze), two sequential copolymers, poly(Pro-Aze) and poly(Aze3-Pro3), have been investigated. All polymers containing Aze are more flexible than poly(Pro). This is a consequence of an increased number of permitted conformational states for the Aze residue, as compared to Pro, when they are incorporated into a polypeptide, as well as of a lessened cooperativity of the trans-cis transition. The results of the computation can be used to interpret the observed physical properties of poly(Aze) and of its copolymers.

Azetidinecarboxylic Acid↗
PubMed1988

Amino acid sequences and homopolymer-forming ability of the intermediate filament proteins from an invertebrate epithelium.

Intermediate filaments (IF) isolated from the oesophagus epithelium of the snail Helix pomatia contain two polypeptides of mol. wt 66,000 (A) and 52,000 (B), which we have now characterized by in vitro self-assembly studies and by protein sequences. A and B can each form morphologically normal IF and share extended regions of sequence identity. All A-specific sequences seem to locate to an extension of the carboxyl-terminal domain. Although the Helix protein(s) reveal the IF-consensus sequences at the ends of the coiled-coil, the remainder of the rod domain shows conservation of sequence principles rather than extended homology, when compared with any subtype of vertebrate IF proteins. Interestingly, the Helix proteins have the longer coil 1b domain found in nuclear lamins and not in cytoplasmic IF proteins of vertebrates. They lack, however, the karyophilic signal sequence typical for lamins. Obvious implications for IF evolution and structure are discussed.

Amino Acid Sequence↗
PubMed2005

Polyglutamine homopolymers having 8-45 residues form slablike beta-crystallite assemblies.

At least nine inherited neurodegenerative diseases, including Huntington's, are caused by poly(L-glutamine) (polyGln, polyQ) expansions > 35-40 repeats in widely or ubiquitously expressed proteins. Except for their expansions, these proteins have no sequence homologies, and their functions mostly remain unknown. Although each disease is characterized by a distinct pathology specific to a subset of neuronal cells, the formation of neuronal intranuclear aggregates containing protein with an expanded polyQ is the hallmark and common feature to most polyQ disorders. The neurodegeneration is thought to be caused by a toxic gain of function that occurs at the protein level and depends on the length of the expansion: Longer repeats cause earlier age of onset and more severe symptoms. To address whether there is a structural difference between polyQ having < 40 versus > 40 residues, we undertook an X-ray fiber diffraction study of synthetic polyQ peptides having varying numbers of residues: Ac-Q8-NH2, D2Q15K2, K2Q28K2, and K2Q45K2. These particular lengths bracket both the range of normalcy (9-36 repeats) and the pathological (45 repeats), and therefore could be indicative of the structural changes expected in expanded polyQ domains. Contrary to expectations of different length-dependent morphologies, we accounted for all the X-ray patterns by slablike, beta-sheet structures, approximately 20 A thick in the beta-chain direction, all having similar monoclinic lattices. Moreover, the slab thickness indicates that K2Q45K2, rather than forming a water-filled nanotube, must form multiple reverse turns.

Amino Acids↗
PubMed1999

Polycations. 5. Inducement of psi-DNA circular dichroism signals for duplex deoxyribonucleotide homopolymers by polycationic strings.

Atypical circular dichroism intensity enhancements previously associated with Psi-DNA condensates are reported for poly(dG-dC):poly(dG-dC) and poly(dA-dT):poly(dA-dT) upon addition to them of a polycationic string salt. Polycationic strings are organic species incorporating several cationic sites in a linear array through the molecule. The effect observed herein with a small molecule model system holds promise for elucidation of the structural details associated with Psi-DNA condensate formation.

Cations↗
PubMed2000

Polyhydroxyalkanoate accumulation in Burkholderia sp.: a molecular approach to elucidate the genes involved in the formation of two homopolymers consisting of short-chain-length 3-hydroxyalkanoic acids.

Burkholderia sp. accumulates polyhydrox-yalkanoates (PHAs) containing 3-hydroxybutyrate and 3-hydroxy-4-pentenoic acid when grown on mineral media under limited phosphate or nitrogen, and using sucrose or gluconate as a carbon and energy source. Solvent fractionation and NMR spectroscopic characterization of these polyesters revealed the simultaneous accumulation of two homopolyesters rather than a co-polyester with random sequence distribution of the monomers [Valentin HE, Berger PA, Gruys KJ, Rodrigues MFA, Steinbuchel A, Tran M, Asrar J (1999) Macromolecules 32: 7389-7395]. To understand the genetic requirements for such unusual polyester accumulation, we probed total genomic DNA from Burkholderia sp. by Southern hybridization experiments using phaC-specific probes. These experiments indicated the presence of more than one PHA synthase gene within the genome of Burkholderia sp. However, when total genomic DNA from Burkholderia sp. was used to complement a PHA-negative mutant of Ralstonia eutropha for PHA accumulation, only one PHA synthase gene was obtained resembling the R. eutropha type of PHA synthases, based on amino acid sequence similarity. In addition to the PHA synthase gene, based on high sequence homology, genes encoding a beta-ketothiolase and acetoacetyl-CoA reductase were identified in a gene cluster with the PHA synthase gene. The arrangement of the three genes is quite similar to the R. eutropha poly-beta-hydroxybutyrate biosynthesis operon.

Acyltransferases↗