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Abraham J Koster

Publications and source records attributed to Abraham J Koster.

16 recordsLinked to original sources
PubMed2006

High-resolution electron tomography study of an industrial Ni-Mo/gamma-Al2O3 hydrotreating catalyst.

The growing demand for high-quality transportation fuels requires their cost-effective production by hydrodesulfurization of crude oils using heterogeneous catalysts. To study the three-dimensional (3D) structure of such a commercial, sulfided Ni-Mo/gamma-Al2O3 catalyst, electron tomography was applied. The MoS2 particles form an interconnected complex structure within the mesopores of the alumina support. Spatial organization, morphology, and orientation of the MoS2 particles in the pores were resolved with sufficient accuracy to display the 6-A-spaced MoS2 crystal planes. The proximity of the MoS2 edge planes and more loosely interacting MoS2 basal planes to the alumina support showed the presence of pores smaller than 3 nm, which was confirmed by physisorption experiments. The actual shape of the MoS2 particles cannot be described by simple models as derived from studies on model catalysts. Electron tomography is a unique tool to study the actual 3D structure of complex industrial catalysts with sub-nanometer resolution.

Letter↗
PubMed2006

Immuno-electron tomography of ER exit sites reveals the existence of free COPII-coated transport carriers.

Transport from the endoplasmic reticulum (ER) to the Golgi complex requires assembly of the COPII coat complex at ER exit sites. Recent studies have raised the question as to whether in mammalian cells COPII coats give rise to COPII-coated transport vesicles or instead form ER sub-domains that collect proteins for transport via non-coated carriers. To establish whether COPII-coated vesicles do exist in vivo, we developed approaches to combine quantitative immunogold labelling (to identify COPII) and three-dimensional electron tomography (to reconstruct entire membrane structures). In tomograms of both chemically fixed and high-pressure-frozen HepG2 cells, immuno-labelled COPII was found on ER-associated buds as well as on free approximately 50-nm diameter vesicles. In addition, we identified a novel type of COPII-coated structure that consists of partially COPII-coated, 150-200-nm long, dumb-bell-shaped tubules. Both COPII-coated carriers also contain the SNARE protein Sec22b, which is necessary for downstream fusion events. Our studies unambiguously establish the existence of free, bona fide COPII-coated transport carriers at the ER-Golgi interface, suggesting that assembly of COPII coats in vivo can result in vesicle formation.

COP-Coated Vesicles↗
PubMed2006

Actin filaments are involved in the maintenance of Golgi cisternae morphology and intra-Golgi pH.

Here we examine the contribution of actin dynamics to the architecture and pH of the Golgi complex. To this end, we have used toxins that depolymerize (cytochalasin D, latrunculin B, mycalolide B, and Clostridium botulinum C2 toxin) or stabilize (jasplakinolide) filamentous actin. When various clonal cell lines were examined by epifluorescence microscopy, all of these actin toxins induced compaction of the Golgi complex. However, ultrastructural analysis by transmission electron microscopy and electron tomography/three-dimensional modelling of the Golgi complex showed that F-actin depolymerization first induces perforation/fragmentation and severe swelling of Golgi cisternae, which leads to a completely disorganized structure. In contrast, F-actin stabilization results only in cisternae perforation/fragmentation. Concomitantly to actin depolymerization-induced cisternae swelling and disorganization, the intra-Golgi pH significantly increased. Similar ultrastructural and Golgi pH alkalinization were observed in cells treated with the vacuolar H+ -ATPases inhibitors bafilomycin A1 and concanamycin A. Overall, these results suggest that actin filaments are implicated in the preservation of the flattened shape of Golgi cisternae. This maintenance seems to be mediated by the regulation of the state of F-actin assembly on the Golgi pH homeostasis.

Actin Cytoskeleton↗
PubMed2006

A vaccinia virus lacking A10L: viral core proteins accumulate on structures derived from the endoplasmic reticulum.

The assembly of the intracellular mature virus (IMV) of vaccinia virus (VV), the prototype member of the poxviridae, is poorly understood and controversial. We have previously proposed that the IMV is composed of a continuous double-membraned cisterna derived from the smooth ER, whereby the genome-containing core is enwrapped by a part of this cisterna. In the present study we characterize a mutant virus in which the synthesis of the major core protein A10L can be conditionally expressed. Without A10L, IMVs are not made; immature viruses (IVs) and regularly stacked membrane structures that contain viral DNA, accumulate instead. By immunolabelling of thawed cryo-sections these stacks contain most of the viral core proteins and low levels of viral membrane proteins. Importantly, the stacked membranes could be labelled with antibodies to an ER marker protein, implying that they are derived from this cellular compartment. By electron tomography (ET) on semi-thin cryo-sections we show that the membranes of the stacks are continuous with the membranes of the IVs. Direct continuities with ER cisternae, to which the stacks are tightly apposed, were, however, not unequivocally seen. Finally, ET revealed how the IV membranes separated to become two-membrane profiles. Taken together, this study shows that VV core proteins and the viral DNA can coassemble onto ER-derived membranes that are continuous with the membranes of the IVs.

Animals↗
PubMed2005

Correlative microscopy and electron tomography of GFP through photooxidation.

We have developed a simple correlative photooxidation method that allows for the direct ultrastructural visualization of the green fluorescent protein (GFP) upon illumination. The method, termed GRAB for GFP recognition after bleaching, uses oxygen radicals generated during the GFP bleaching process to photooxidize 3,3'-diaminobenzidine (DAB) into an electron-dense precipitate that can be visualized by routine electron microscopy and electron tomography. The amount of DAB product produced by the GRAB method appears to be linear with the initial fluorescence, and the resulting images are of sufficient quality to reveal detailed spatial information. This is exemplified by the observed intra-Golgi stack and intracisternal distribution of a human Golgi resident glycosylation enzyme, N-acetylgalactosaminyltransferase-2 fused either to enhanced GFP or CFP.

3,3'-Diaminobenzidine↗
PubMed2004

Golgi enzymes are enriched in perforated zones of golgi cisternae but are depleted in COPI vesicles.

In the most widely accepted version of the cisternal maturation/progression model of intra-Golgi transport, the polarity of the Golgi complex is maintained by retrograde transport of Golgi enzymes in COPI-coated vesicles. By analyzing enzyme localization in relation to the three-dimensional ultrastructure of the Golgi complex, we now observe that Golgi enzymes are depleted in COPI-coated buds and 50- to 60-nm COPI-dependent vesicles in a variety of different cell types. Instead, we find that Golgi enzymes are concentrated in the perforated zones of cisternal rims both in vivo and in a cell-free system. This lateral segregation of Golgi enzymes is detectable in some stacks during steady-state transport, but it was significantly prominent after blocking endoplasmic reticulum-to-Golgi transport. Delivery of transport carriers to the Golgi after the release of a transport block leads to a diminution in Golgi enzyme concentrations in perforated zones of cisternae. The exclusion of Golgi enzymes from COPI vesicles and their transport-dependent accumulation in perforated zones argues against the current vesicle-mediated version of the cisternal maturation/progression model.

Animals↗
PubMed2004

Secretory traffic triggers the formation of tubular continuities across Golgi sub-compartments.

The organization of secretory traffic remains unclear, mainly because of the complex structure and dynamics of the secretory pathway. We have thus studied a simplified system, a single synchronized traffic wave crossing an individual Golgi stack, using electron tomography. Endoplasmic-reticulum-to-Golgi carriers join the stack by fusing with cis cisternae and induce the formation of intercisternal tubules, through which they redistribute their contents throughout the stack. These tubules seem to be pervious to Golgi enzymes, whereas Golgi vesicles are depleted of both enzymes and cargo. Cargo then traverses the stack without leaving the cisternal lumen. When cargo exits the stack, intercisternal connections disappear. These findings provide a new view of secretory traffic that includes dynamic intercompartment continuities as key players.

Biological Transport↗
PubMed2004

3-D Structure of multilaminar lysosomes in antigen presenting cells reveals trapping of MHC II on the internal membranes.

In late endosomes and lysosomes of antigen presenting cells major histocompatibility complex class II (MHC II) molecules bind peptides from degraded internalized pathogens. These compartments are called MHC class II compartments (MIICs), and from here peptide-loaded MHC II is transported to the cell surface for presentation to helper T-lymphocytes to generate an immune response. Recent studies from our group in mouse dendritic cells indicate that the MHC class II on internal vesicles of multivesicular late endosomes or multivesicular bodies is the main source of MHC II at the plasma membrane. We showed that dendritic cell activation triggers a back fusion mechanism whereby MHC II from the inner membranes is delivered to the multivesicular bodies' outer membrane. Another type of MIIC in B-lymphocytes and dendritic cells is more related to lysosomes and often appears as a multilaminar organelle with abundant MHC II-enriched internal membrane sheets. These multilaminar lysosomes have a functioning peptide-loading machinery, but to date it is not clear whether peptide-loaded MHC II molecules from the internal membranes can make their way to the cell surface and contribute to T cell activation. To obtain detailed information on the membrane organization of multilaminar lysosomes and investigate possible escape routes from the lumen of this organelle, we performed electron tomography on cryo-immobilized B-lymphocytes and dendritic cells. Our high-resolution 3-D reconstructions of multilaminar lysosomes indicate that their membranes are organized in such a way that MHC class II may be trapped on the inner membranes, without the possibility to escape to the cell surface.

Antigen-Presenting Cells↗
PubMed2003

Involvement of the endoplasmic reticulum in peroxisome formation.

The traditional view holds that peroxisomes are autonomous organelles multiplying by growth and division. More recently, new observations have challenged this concept. Herein, we present evidence supporting the involvement of the endoplasmic reticulum (ER) in peroxisome formation by electron microscopy, immunocytochemistry and three-dimensional image reconstruction of peroxisomes and associated compartments in mouse dendritic cells. We found the peroxisomal membrane protein Pex13p and the ATP-binding cassette transporter protein PMP70 present in specialized subdomains of the ER that were continuous with a peroxisomal reticulum from which mature peroxisomes arose. The matrix proteins catalase and thiolase were only detectable in the reticula and peroxisomes. Our results suggest the existence of a maturation pathway from the ER to peroxisomes and implicate the ER as a major source from which the peroxisomal membrane is derived.

ATP-Binding Cassette Transporters↗
PubMed2003

ER-to-Golgi carriers arise through direct en bloc protrusion and multistage maturation of specialized ER exit domains.

Protein transport between the ER and the Golgi in mammalian cells occurs via large pleiomorphic carriers, and most current models suggest that these are formed by the fusion of small ER-derived COPII vesicles. We have examined the dynamics and structural features of these carriers during and after their formation from the ER by correlative video/light electron microscopy and tomography. We found that saccular carriers containing either the large supramolecular cargo procollagen or the small diffusible cargo protein VSVG arise through cargo concentration and direct en bloc protrusion of specialized ER domains in the vicinity of COPII-coated exit sites. This formation process is COPII dependent but does not involve budding and fusion of COPII-dependent vesicles. Fully protruded saccules then move centripetally, evolving into one of two types of carriers (with distinct kinetic and structural features). These findings provide an alternative framework for analysis of ER-to-Golgi traffic.

2,2'-Dipyridyl↗
PubMed2003

Electron microscopy in cell biology: integrating structure and function.

Electron microscopy (EM) is at the highest-resolution limit of a spectrum of complementary morphological techniques. When combined with molecular detection methods, EM is the only technique with sufficient resolution to localize proteins to small membrane subdomains in the context of the cell. Recent procedural and technical developments have increasingly improved the power of EM as a cell-biological tool.

Animals↗
PubMedDate not supplied

Three-dimensional localization of ultrasmall immuno-gold labels by HAADF-STEM tomography.

The localization of scarce antigens in thin sections of biological material can be accomplished by pre-embedment labeling with ultrasmall immuno-gold labels. Moreover, with this method, labeling is not restricted to the section surface but occurs throughout the section volume. Thus, when combined with electron tomography, antigens can be localized in three dimensions in relation to the 3D (three-dimensional) ultrastructure of the cell. However, for visualization in a transmission electron microscope, these labels need to be enlarged by silver or gold enhancement. The increase in particle size reduces the resolution of the antigen detection and the large particles obscure ultrastructural details in the tomogram. In this paper we show for the first time that these problems can be avoided and that ultrasmall gold labels can be localized in three dimensions without the need for gold or silver enhancement by using HAADF-STEM (high angular annular dark-field-scanning transmission electron microscopy) tomography. This method allowed us to three-dimensionally localize Aurion ultrasmall goat anti-rabbit immuno-gold labels on sections of Epon-embedded, osmium-uranium-lead-stained biological material. Calculations show that a 3D reconstruction obtained from HAADF-STEM projection images can be spatially aligned to one obtained from transmission electron microscopy (TEM) projections with subpixel accuracy. We conclude that it is possible to combine the high-fidelity structural information of TEM tomograms with the ultrasmall label localization ability of HAADF-STEM tomograms.

Animals↗