Mechanism-based irreversible inhibitors of cytokinin dehydrogenase

The effects of three N(6)-substituted aminopurine derivatives containing either allenic or acetylenic side-chains on in vitro and in vivo cytokinin dehydrogenase (CKX; EC 1.5.99.12) activities were determined. At concentrations < or = 100 microM, the acetylenic derivative (HA-2) had no effect on in vitro CKX activity. In contrast, the two allenic derivatives (HA-1, HA-8) inhibited in vitro CKX activity in a dose-dependent manner with 50% inhibition occurring at HA-1 and HA-8 concentrations of 9.0 and 0.4 microM (respectively). HA-8 inhibited the degradation of both the free bases and ribosides of N6-(2-isopentenyl)adenine and zeatin. Pretreatment with HA-8 inhibited CKX activity in both a time- and concentration-dependent manner. In contrast to the reversible phenylurea inhibitor N-(chloro-4-pyridyl)-N'-phenylurea, inhibition of CKX activity by HA-8 was not relieved by 24 h of dialysis. Both HA-1 and HA-8 (but not HA-2) inhibited the metabolism of exogenous [3H]-N(6)-(2-isopentenyl)adenosine in excised aseptic potato (Solanum tuberosum) leaves. These results demonstrate that HA-8 is a mechanism-based irreversible (suicide) inhibitor of CKX and indicate that it may be useful in determining the role of CKX in cytokinin homeostasis in planta.     

Quantitative and dynamic assessment of the contribution of the ER to phagosome formation

Phagosomes were traditionally thought to originate from an invagination and scission of the plasma membrane to form a distinct intracellular vacuole. An alternative model implicating the endoplasmic reticulum (ER) as a major component of nascent and maturing phagosomes was recently proposed (Gagnon et al., 2002). To reconcile these seemingly disparate hypotheses, we used a combination of biochemical, fluorescence imaging, and electron microscopy techniques to quantitatively and dynamically assess the contribution of the plasmalemma and of the ER to phagosome formation and maturation. We could not verify even a transient physical continuity between the ER and the plasma membrane, nor were we able to detect a significant contribution of the ER to forming or maturing phagosomes in either macrophages or dendritic cells. Instead, our data indicate that the plasma membrane is the main constituent of nascent and newly formed phagosomes, which are progressively remodeled by fusion with endosomal and eventually lysosomal compartments as phagosomes mature into acidic, degradative organelles.     

A genome screen for linkage disequilibrium in HLA-DRB1*15-positive Germans with multiple sclerosis based on 4666 microsatellite markers

Multiple sclerosis (MS) is a demyelinating disorder of the central nervous system with putative autoimmune aetiology and complex genetic background. Here, we report the results of a genome screen for linkage disequilibrium (LD) by using 6000 microsatellite markers in 198 HLA-DRB1*15-positive MS patients and 198 unrelated controls (pooled DNA); 4666 analysed markers could be included in the resulting association map, from which 87 revealed significant differences between MS cases and controls.     

"Sausage-string" appearance of arteries and arterioles can be caused by an instability of the blood vessel wall

Vascular damage induced by acute hypertension is preceded by a peculiar pattern where blood vessels show alternating regions of constrictions and dilations ("sausages on a string"). The pattern occurs in the smaller blood vessels, and it plays a central role in causing the vascular damage. A related vascular pattern has been observed in larger vessels from several organs during angiography. In the larger vessels the occurrence of the pattern does not appear to be related to acute hypertension. A unifying feature between the phenomenon in large and small vessels seems to be an increase in vascular wall tension. Despite much research, the mechanisms underlying the sausage pattern have remained unknown. Here we present an anisotropic model of the vessel wall and show that the sausage pattern can arise because of an instability of the vessel wall. The model reproduces many of the key features observed experimentally. Most importantly, it suggests that the "sausaging" phenomenon is neither caused by a mechanical failure of the vessel wall due to a high blood pressure nor is it due to standing pressure waves caused by the beating of the heart. Rather, it is the expression of a general instability phenomenon. Experimental data suggest that the structural changes induced by the instability may cause secondary damage to the wall of small arteries and arterioles in the form of endothelial hyperpermeability followed by local fibrinoid necrosis of the vascular wall.     

Laboratory and histopathologic comparative study of internal ultrasound-assisted lipoplasty and tumescent lipoplasty

Despite the advantages of using internal ultrasound-assisted lipoplasty instead of the classic tumescent lipoplasty, such as reduced bleeding and tissue damage, the authors found no objective or comparative study of these techniques in humans. For this reason, they conducted a clinical study to determine the amount of bleeding and tissue damage caused by each of the techniques. A simple clinical assay was accomplished at the Jalisco Plastic Surgery Institute on seven female patients scheduled for abdominal lipectomy. Two similar sections of the surgical area were marked for lipoplasty techniques: classic tumescent lipoplasty on one side and internal ultrasound-assisted lipoplasty on the other. Both areas were treated simultaneously by surgeons experienced in each technique. Laboratory tests and histologic studies were performed on the aspirated material and the manipulated tissue, respectively. The fluids sent to the laboratory were analyzed to determine the amount of bleeding and tissue damage. In the laboratory, the degree of lesion and tissue damage was evaluated in the dermis, nerves, blood vessels, and adipose cells. With internal ultrasound-assisted lipoplasty, indicators of tissue damage such as glutamic oxalacetic transaminase, pyruvic oxalacetic transaminase, cholinesterase, and myoglobin showed higher values than with tumescent lipoplasty. The same was found for hemoglobin levels and in the histologic data indicative of tissue damage; both values were statistically significant at < 0.001. Internal ultrasound-assisted lipoplasty was not demonstrated to be more innocuous or to have a selective effect in adipose cells, and it generally resulted in more tissue damage and bleeding than the classic tumescent technique.     

Genetically targeted chromophore-assisted light inactivation

Studies of protein function would be facilitated by a general method to inactivate selected proteins in living cells noninvasively with high spatial and temporal precision. Chromophore-assisted light inactivation (CALI) uses photochemically generated, reactive oxygen species to inactivate proteins acutely, but its use has been limited by the need to microinject dye-labeled nonfunction-blocking antibodies. We now demonstrate CALI of connexin43 (Cx43) and alpha1C L-type calcium channels, each tagged with one or two small tetracysteine (TC) motifs that specifically bind the membrane-permeant, red biarsenical dye, ReAsH. ReAsH-based CALI is genetically targeted, requires no antibodies or microinjection, and inactivates each protein by approximately 90% in <30 s of widefield illumination. Similar light doses applied to Cx43 or alpha1C tagged with green fluorescent protein (GFP) had negligible to slight effects with or without ReAsH exposure, showing the expected molecular specificity. ReAsH-mediated CALI acts largely via singlet oxygen because quenchers or enhancers of singlet oxygen respectively inhibit or enhance CALI.     

DSMM: a Database of Simulated Molecular Motions

We describe a Database of Simulated Molecular Motions (DSMM). This database is designed to serve as a single searchable site for locating movies and animations from simulations of biomolecules. DSMM is accessible via a webserver at: http://projects.villa-bosch.de/mcm/database/dsmm.     

Superimposing polymorphism: the case of a point mutation within a polymorphic Alu insertion

The COL3A1 Alu insertion is a member of the AluY subfamily. It has been found to be absent in non-human primates and polymorphic in worldwide human populations. The integration of the element into the human genome seems to have preceded the initial migration(s) of anatomically modern humans out of the African continent. Although the insertion has been detected in populations from all the continents, its highest frequency values are located within sub-Saharan Africa. The sequence alignment of the COL3A1 insertion from several African individuals revealed a bi-allelic single nucleotide polymorphism (SNP) at the downstream terminus of the element's poly-A tract. Once discovered, a selective PCR procedure was designed to determine the frequency of both alleles in 19 worldwide populations. The A-allele in this binary SNP experiences a clinal increase in the eastward direction from Africa to Southeast Asia and Mongolia, reaching fixation in the two latter regions. The T variant, on the other hand, exhibits a westward clinal increase outside of Africa, with its lowest frequency in Asia and achieving fixation in northern Europe. The presence of this internal SNP extends the usefulness provided by the polymorphic Alu insertion (PAI). It is possible that superimposing polymorphisms like this one found in the COL3A1 locus may accentuate signals from genetic drift events allowing for visualization of recent dispersal patterns.