Normal metabolism but different physical properties of myelin from mice deficient in proteolipid protein

Proteolipid protein (PLP) is the primary protein component of CNS myelin, yet myelin from the PLPnull mouse has only minor ultrastructural abnormalities. Might compensation for a potentially unstable structure involve increased myelin synthesis and turnover? This was not the case; neither accumulation nor in vivo synthesis rates for the myelin- specific lipid cerebroside was altered in PLPnull mice relative to wild-type (wt) animals. However, the yield of myelin from PLPnull mice, assayed as levels of cerebroside, was only about 55% of wt control levels. Loss of myelin occurred during initial centrifugation of brain homogenate at 20,000g for 20 min, which is sufficient to sediment almost all myelin from wt mice. Cerebroside-containing fragments from PLPnull mice remaining in the supernatant could be sedimented by more stringent centrifugation, 100,000g for 60 min. Both the rapidly. and the more slowly sedimenting cerebroside-containing membranes banded at the 0.85/0.32 M sucrose interface of a density gradient, as did myelin from wt mice. These results suggest at least some myelin from PLPnull mice differs from wt myelin with respect to physical stability (fragmented into smaller particles during dispersion) and/or density. Alternatively, slowly sedimenting cerebroside-containing particles could be myelin precursor membranes that, lacking PLP, were retarded in their processing toward mature myelin and thus differ from mature myelin in physical properties. If this is so, recently synthesized cerebroside should be preferentially found in these "slower-sedimenting" myelin precursor fragments. Metabolic tracer experiments showed this was not the case. We conclude that PLPnull myelin is physically less stable and/or less dense than wt myelin. (C) 2003 Wiley- Liss, Inc

A domino ring-opening/epoxidation of 1,2-dioxines

Copyright © 2004 American Chemical SocietyWhen allowed to react with alkaline hydrogen peroxide, monocyclic 1,2-dioxines ring-open to their isomeric -hydroxyenone intermediates which are rapidly epoxidized to afford trans-4-hydroxy-2,3-epoxyketones in 21-81% yield. In the case of meso-1,2-dioxines, Co(II) complex catalyzed asymmetric ring-opening of the 1,2-dioxine may be employed to furnish enantioenriched epoxide

Dynamics of Lignin: Molecular Dynamics and Neutron Scattering

Lignocellulosic biomass, the major secondary plant cell wall material, is composed of three major components: lignin, hemicellulose, and cellulose. Lignin, an amorphous polymer that does not have a regular chemical structure, plays an important role in the recalcitrance of lignocellulosic biomass to deconstruction by blocking enzymatic hydrolysis of cellulose. Understanding the dynamics of the lignin polymer is fundamental for technological applications involving biomass, such as biofuel production. In this chapter, we discuss the application of neutron scattering and molecular dynamics simulation used to study the atomic dynamics of lignin. We focus on glass transition, the technologically most important dynamical processes of lignin. We explain the impact of environmental factors, such as hydration and temperature, on the magnitude of lignin atomic fluctuations and the relaxation processes at temperatures above and below the glass transition temperature. © 2019 American Chemical Society.Office of Science U.S. Department of Energy U.S. Department of Energy: FWP ERKP752This research was supported by the Genomic Science Program, Office of Biological and Environmental Research, U. S. Department of Energy (DOE), under Contract FWP ERKP752. This research used resources of the (i) National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U. S. Department of Energy under Contract No. DE-AC02-05CH11231; and (ii) the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory

Structure and Function of Glycosylated Tandem Repeats from Candida albicans Als Adhesins ▿ †

Tandem repeat (TR) regions are common in yeast adhesins, but their structures are unknown, and their activities are poorly understood. TR regions in Candida albicans Als proteins are conserved glycosylated 36-residue sequences with cell-cell aggregation activity (J. M. Rauceo, R. De Armond, H. Otoo, P. C. Kahn, S. A. Klotz, N. K. Gaur, and P. N. Lipke, Eukaryot. Cell 5:1664–1673, 2006). Ab initio modeling with either Rosetta or LINUS generated consistent structures of three-stranded antiparallel β-sheet domains, whereas randomly shuffled sequences with the same composition generated various structures with consistently higher energies. O- and N-glycosylation patterns showed that each TR domain had exposed hydrophobic surfaces surrounded by glycosylation sites. These structures are consistent with domain dimensions and stability measurements by atomic force microscopy (D. Alsteen, V. Dupres, S. A. Klotz, N. K. Gaur, P. N. Lipke, and Y. F. Dufrene, ACS Nano 3:1677–1682, 2009) and with circular dichroism determination of secondary structure and thermal stability. Functional assays showed that the hydrophobic surfaces of TR domains supported binding to polystyrene surfaces and other TR domains, leading to nonsaturable homophilic binding. The domain structures are like “classic” subunit interaction surfaces and can explain previously observed patterns of promiscuous interactions between TR domains in any Als proteins or between TR domains and surfaces of other proteins. Together, the modeling techniques and the supporting data lead to an approach that relates structure and function in many kinds of repeat domains in fungal adhesins

Metal-Mediated Affinity and Orientation Specificity in a Computationally Designed Protein Homodimer

Computationally designing protein-protein interactions with high affinity and desired orientation is a challenging task. Incorporating metal-binding sites at the target interface may be one approach for increasing affinity and specifying the binding mode, thereby improving robustness of designed interactions for use as tools in basic research as well as in applications from biotechnology to medicine. Here we describe a Rosetta-based approach for the rational design of a protein monomer to form a zinc-mediated, symmetric homodimer. Our metal interface design, named MID1 (NESG target ID OR37), forms a tight dimer in the presence of zinc (MID1-zinc) with a dissociation constant <30 nM. Without zinc the dissociation constant is 4 μM. The crystal structure of MID1-zinc shows good overall agreement with the computational model, but only three out of four designed histidines coordinate zinc. However, a histidine-to-glutamate point mutation resulted in four-coordination of zinc, and the resulting metal binding site and dimer orientation closely matches the computational model (Cα RMSD = 1.4 Å)