ABSTRACT
We demonstrate absolute quantitative mass density mapping in three dimensions of frozen-hydrated biological matter with an isotropic resolution of 180 nm. As model for a biological system we use Chlamydomonas cells in buffer solution confined in a microcapillary. We use ptychographic X-ray computed tomography to image the entire specimen, including the 18 µm-diameter capillary, thereby providing directly an absolute mass density measurement of biological matter with an uncertainty of about 6%. The resulting maps have sufficient contrast to distinguish cells from the surrounding ice and several organelles of different densities inside the cells. Organelles are identified by comparison with a stained, resin-embedded specimen, which can be compared with established transmission electron microscopy results. For some identified organelles, the knowledge of their elemental composition reduces the uncertainty of their mass density measurement down to 1% with values consistent with previous measurements of dry weight concentrations in thin cellular sections by scanning transmission electron microscopy. With prospects of improving the spatial resolution in the near future, we expect that the capability of non-destructive three-dimensional mapping of mass density in biological samples close to their native state becomes a valuable method for measuring the packing of organic matter on the nanoscale.
Subject(s)
Chlamydomonas reinhardtii/physiology , Chlamydomonas reinhardtii/ultrastructure , Imaging, Three-Dimensional/methods , Organelles/ultrastructure , Tomography, X-Ray Computed/methods , FreezingABSTRACT
Oligobenzamide inhibitors of the p53-hDM2 protein-protein interaction are described.
Subject(s)
Benzamides/pharmacology , Enzyme Inhibitors/pharmacology , Proto-Oncogene Proteins c-mdm2/antagonists & inhibitors , Tumor Suppressor Protein p53/antagonists & inhibitors , Benzamides/chemistry , Binding Sites , Enzyme Inhibitors/chemistry , Humans , Models, Molecular , Molecular Structure , Protein Binding/drug effects , Proto-Oncogene Proteins c-mdm2/metabolism , Structure-Activity Relationship , Tumor Suppressor Protein p53/metabolismABSTRACT
A current goal in synthetic chemistry is the design and synthesis of molecules that adopt well defined conformations-so called foldamers. In this manuscript we describe a modular approach for construction of rod shaped para-oligobenzamide molecules. Our approach permits regiospecific incorporation of side chains through a phenolic ether linkage on the scaffold; a feature that partly restricts the conformation of the rod through intramolecular hydrogen-bonding.
Subject(s)
Benzamides/chemistry , Benzamides/chemical synthesis , Crystallography, X-Ray , Ether/chemistry , Hydrogen Bonding , Models, Molecular , Molecular Conformation , Monte Carlo MethodABSTRACT
We investigated the influence of the polyunsaturated docosahexaenoic acid (22:6n-3; DHA) on the constitutive expression of choline acetyltransferase (ChAT) in native and induced expression in differentiated cholinergic cells NG108-15 grown in serum-free medium. Elimination of serum-derived trophic support resulted in growth arrest and a strong decrease of ChAT activity. In either conditions, DHA largely rescued general indicators of cell growth and function, and partially prevented the decrease of ChAT activity. However, the maximal effect on general cell state in native and differentiated cells, and ChAT activity in native cells, was reached at or below 10 mumol/l of DHA. In contrast, maximal induction of ChAT activity in differentiated cells required about six times higher concentrations of DHA. These data thus demonstrate stimulatory effect of DHA on ChAT activity that is independent of its general cell protective properties.
