Caspase-3-generated fragment of gelsolin: effector of morphological change in apoptosis

The caspase-3 (CPP32, apopain, YAMA) family of cysteinyl proteases has been implicated as key mediators of apoptosis in mammalian cells. Gelsolin was identified as a substrate for caspase-3 by screening the translation products of small complementary DNA pools for sensitivity to cleavage by caspase-3. Gelsolin was cleaved in vivo in a caspase-dependent manner in cells stimulated by Fas. Caspase-cleaved gelsolin severed actin filaments in vitro in a Ca2+-independent manner. Expression of the gelsolin cleavage product in multiple cell types caused the cells to round up, detach from the plate, and undergo nuclear fragmentation. Neutrophils isolated from mice lacking gelsolin had delayed onset of both blebbing and DNA fragmentation, following apoptosis induction, compared with wild-type neutrophils. Thus, cleaved gelsolin may be one physiological effector of morphologic change during apoptosis.

Human aspartic protease memapsin 2 cleaves the beta-secretase site of beta-amyloid precursor protein

The cDNAs of two new human membrane-associated aspartic proteases, memapsin 1 and memapsin 2, have been cloned and sequenced. The deduced amino acid sequences show that each contains the typical pre, pro, and aspartic protease regions, but each also has a C-terminal extension of over 80 residues, which includes a single transmembrane domain and a C-terminal cytosolic domain. Memapsin 2 mRNA is abundant in human brain. The protease domain of memapsin 2 cDNA was expressed in Escherichia coli and was purified. Recombinant memapsin 2 specifically hydrolyzed peptides derived from the beta-secretase site of both the wild-type and Swedish mutant beta-amyloid precursor protein (APP) with over 60-fold increase of catalytic efficiency for the latter. Expression of APP and memapsin 2 in HeLa cells showed that memapsin 2 cleaved the beta-secretase site of APP intracellularly. These and other results suggest that memapsin 2 fits all of the criteria of beta-secretase, which catalyzes the rate-limiting step of the in vivo production of the beta-amyloid (Abeta) peptide leading to the progression of Alzheimer's disease. Recombinant memapsin 2 also cleaved a peptide derived from the processing site of presenilin 1, albeit with poor kinetic efficiency. Alignment of cleavage site sequences of peptides indicates that the specificity of memapsin 2 resides mainly at the S(1)' subsite, which prefers small side chains such as Ala, Ser, and Asp.

Insights into the molecular basis of leukocyte tethering and rolling revealed by structures of P- and E-selectin bound to SLe(X) and PSGL-1

P-, E- and L-selectin constitute a family of cell adhesion receptors that mediate the initial tethering and rolling of leukocytes on inflamed endothelium as a prelude to their firm attachment and extravasation into tissues. The selectins bind weakly to sialyl Lewisx (SLe(X))-like glycans, but with high-affinity to specific glycoprotein counterreceptors, including PSGL-1. Here, we report crystal structures of human P- and E-selectin constructs containing the lectin and EGF (LE) domains co-complexed with SLe(X). We also present the crystal structure of P-selectin LE co-complexed with the N-terminal domain of human PSGL-1 modified by both tyrosine sulfation and SLe(X). These structures reveal differences in how E- and P-selectin bind SLe(X) and the molecular basis of the high-affinity interaction between P-selectin and PSGL-1.

Structure of the protease domain of memapsin 2 (beta-secretase) complexed with inhibitor

Memapsin 2 (beta-secretase) is a membrane-associated aspartic protease involved in the production of beta-amyloid peptide in Alzheimer's disease and is a major target for drug design. We determined the crystal structure of the protease domain of human memapsin 2 complexed to an eight-residue inhibitor at 1.9 angstrom resolution. The active site of memapsin 2 is more open and less hydrophobic than that of other human aspartic proteases. The subsite locations from S4 to S2' are well defined. A kink of the inhibitor chain at P2' and the change of chain direction of P3' and P4' may be mimicked to provide inhibitor selectivity.

Structure of Rhodopseudomonas sphaeroides R-26 reaction center

The molecular replacement method has been successfully used to provide a structure for the photosynthetic reaction center of Rhodopseudomonas sphaeroides at 3.7 A resolution. Atomic coordinates derived from the R. viridis reaction center were used in the search structure. The crystallographic R-factor is 0.39 for reflections between 8 and 3.7 A. Validity of the resulting model is further suggested by the visualization of amino acid side chains not included in the R. viridis search structure, and by the arrangements of the reaction centers in the unit cell. In the initial calculations quinones or pigments were not included; nevertheless, in the resulting electron density map, electron density for both quinones QA and QB appears along with the bacteriochlorophylls and bacteriopheophytins. Kinetic analysis of the charge recombination shows that the secondary quinone is fully functional in the R. sphaeroides crystal.

Comprehensive analysis of the clinical immuno-oncology landscape

Advances from immuno-oncology (IO) are changing the standard of care of many types of cancer, and the paradigm of cancer treatments and drug development is being rewritten on a regular basis. Moreover, an unprecedented number of new investigational agents and companies are entering the field of IO. As such, it has become challenging for oncology physicians conducting clinical trials, industry veterans developing IO drugs, and even regulators reviewing novel IO agents to keep track of the rapidly evolving landscape. To help the key stake holders in the field understand the latest IO landscape, we sought to present an unbiased, neutral, scientifically curated, and timely updated analysis of all the current IO agents in clinical development and the clinical trials testing these agents. We based our analyses on information collected from numerous trusted and publicly available sources. We have developed two databases. One database tracks 2004 IO agents (940 in clinical stage and 1064 in preclinical stage) against 303 targets, from 864 companies; the other tracks 3042 active clinical trials of these agents with a target enrollment of 577 076 patients. This report provides key analyses of these data. Furthermore, we will discuss a number of important and actionable trends in the current IO landscape: a large number of companies developing agents against the same IO targets; a rapid increase in the number of anti-PD-1/L1 combination studies, many of which are testing the same combinations and following inefficient patterns; and a significant increase in the number of small, investigator-initiated studies. For each of the findings, we speculate the causes and discuss a few initiatives that aim to address some of these challenges. Finally, by making these landscape analyses available, we aspire to inform the cancer community as they seek to strive for efficiencies and innovation while avoiding duplication.

Arginine methylation of STAT1 modulates IFNalpha/beta-induced transcription

Transcriptional induction by interferons requires the tyrosine and serine phosphorylation of STAT transcription factors. The N-terminal region is highly homologous among the STAT proteins and surrounds a completely conserved arginine residue. Here we demonstrate arginine methylation of STAT1 by the protein arginine methyl-transferase PRMT1 as a novel requirement for IFNalpha/beta-induced transcription. Methyl-thioadenosine, a methyl-transferase inhibitor that accumulates in many transformed cells, inhibits STAT1-mediated IFN responses. This inhibition arises from impaired STAT1-DNA binding due to an increased association of the STAT inhibitor PIAS1 with phosphorylated STAT1 dimers in the absence of arginine methylation. Thus, arginine methylation of STAT1 is an additional posttranslational modification regulating transcription factor function, and alteration of arginine methylation might be responsible for the lack of interferon responsiveness observed in many malignancies.

PRMT1 is the predominant type I protein arginine methyltransferase in mammalian cells

Type I protein arginine methyltransferases catalyze the formation of asymmetric omega-N(G),N(G)-dimethylarginine residues by transferring methyl groups from S-adenosyl-L-methionine to guanidino groups of arginine residues in a variety of eucaryotic proteins. The predominant type I enzyme activity is found in mammalian cells as a high molecular weight complex (300-400 kDa). In a previous study, this protein arginine methyltransferase activity was identified as an additional activity of 10-formyltetrahydrofolate dehydrogenase (FDH) protein. However, immunodepletion of FDH activity in RAT1 cells and in murine tissue extracts with antibody to FDH does not diminish type I methyltransferase activity toward the methyl-accepting substrates glutathione S-transferase fibrillarin glycine arginine domain fusion protein or heterogeneous nuclear ribonucleoprotein A1. Similarly, immunodepletion with anti-FDH antibody does not remove the endogenous methylating activity for hypomethylated proteins present in extracts from adenosine dialdehyde-treated RAT1 cells. In contrast, anti-PRMT1 antibody can remove PRMT1 activity from RAT1 extracts, murine tissue extracts, and purified rat liver FDH preparations. Tissue extracts from FDH(+/+), FDH(+/-), and FDH(-/-) mice have similar protein arginine methyltransferase activities but high, intermediate, and undetectable FDH activities, respectively. Recombinant glutathione S-transferase-PRMT1, but not purified FDH, can be cross-linked to the methyl-donor substrate S-adenosyl-L-methionine. We conclude that PRMT1 contributes the major type I protein arginine methyltransferase enzyme activity present in mammalian cells and tissues.

Structural evidence for gene duplication in the evolution of the acid proteases

X-ray studies of acid proteases indicate a bilobal structure with a well defined active site cleft. An intramolecular twofold symmetry axis relates two topologically similar domains and the active site residues. A possible mechanism for evolution by gene duplication, divergence and gene fusion is presented.

Synthesis, Biochemical Properties and Molecular Modelling Studies of Organometallic Specific Estrogen Receptor Modulators (SERMs), the Ferrocifens and Hydroxyferrocifens: Evidence for an Antiproliferative Effect of Hydroxyferrocifens on both Hormone-Dependent and Hormone-Independent Breast Cancer Cell Lines

A series of ferrocene derivatives based upon the structure of the antiestrogenic drug tamoxifen or of its active metabolite hydroxytamoxifen has been prepared and named by analogy ferrocifens and hydroxyferrocifens. This series includes 1-[4-(O(CH(2))(n)NMe(2))phenyl]-1-phenyl-2-ferrocenyl-but-1-ene and 1-[4-(-O(CH(2))(n)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene, with n=2, 3, 5 and 8, and 1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenylethene. Most of these molecules have been synthesised by McMurry cross-coupling of the appropriate ketones, except for the ethene complexes, which were prepared by a four-step reaction sequence starting from the ferrocenylacetic acid. All these compounds were obtained as mixtures of Z and E isomers. The isomers were separated in the cases of the ferrocenyl derivatives of tamoxifen and hydroxytamoxifen (n=2). No isomerisation of the Z and E isomers occurred in DMSO after one day, while a 50:50 mixture of the isomers was obtained within one hour in chloroform. The X-ray structure of (E)-1-[4-(-O(CH(2))(2)NMe(2))phenyl]-1-(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene has been determined. The relative binding affinity (RBA) values of the hydroxyferrocifens for the estrogen receptor alpha (ERalpha) was good to moderate, with values decreasing progressively with the length of the basic chain. The RBA values found for the estrogen receptor beta (ERbeta) are equal to or slightly less than those found for the alpha form. The lipophilicity of the hydroxyferrocifens are superior to the values found for estradiol and increase with lengthening of the chain. The antiproliferative effects of the four hydroxyferrocifens with n=2, 3, 5 and 8 were studied on four breast cancer cell lines (MCF7, MDA-MB231, RTx6 and TD5) possessing different levels of ERalpha. On MCF7 cells containing high levels of ERalpha, hydroxyferrocifens behave as antiestrogens. At a molarity of 1 microM the effect is close to that of hydroxytamoxifen (used for reference) when n=2 or 5, more marked when n=3, and weaker when n=8. Ferrocene alone has no effect. For the MDA-MB231 cells, classed as a hormone-independent breast cancer cell line, on the other hand, the hydroxyferrocifens show remarkable antiproliferative behaviour while the hydroxytamoxifen is completely inactive. Hydroxyferrocifens therefore show the unique property of being active both on hormone-dependent and on hormone-independent breast cancer cell lines. The molecular modelling study provides some clues for understanding of the antagonist effect of these molecules, while an additional cytotoxic effect due to the vectorised ferrocenyl unit is revealed in some occasions.

A stoichiometric complex of neurexins and dystroglycan in brain

In nonneuronal cells, the cell surface protein dystroglycan links the intracellular cytoskeleton (via dystrophin or utrophin) to the extracellular matrix (via laminin, agrin, or perlecan). Impairment of this linkage is instrumental in the pathogenesis of muscular dystrophies. In brain, dystroglycan and dystrophin are expressed on neurons and astrocytes, and some muscular dystrophies cause cognitive dysfunction; however, no extracellular binding partner for neuronal dystroglycan is known. Regular components of the extracellular matrix, such as laminin, agrin, and perlecan, are not abundant in brain except in the perivascular space that is contacted by astrocytes but not by neurons, suggesting that other ligands for neuronal dystroglycan must exist. We have now identified alpha- and beta-neurexins, polymorphic neuron-specific cell surface proteins, as neuronal dystroglycan receptors. The extracellular sequences of alpha- and beta-neurexins are largely composed of laminin-neurexin-sex hormone-binding globulin (LNS)/laminin G domains, which are also found in laminin, agrin, and perlecan, that are dystroglycan ligands. Dystroglycan binds specifically to a subset of the LNS domains of neurexins in a tight interaction that requires glycosylation of dystroglycan and is regulated by alternative splicing of neurexins. Neurexins are receptors for the excitatory neurotoxin alpha-latrotoxin; this toxin competes with dystroglycan for binding, suggesting overlapping binding sites on neurexins for dystroglycan and alpha-latrotoxin. Our data indicate that dystroglycan is a physiological ligand for neurexins and that neurexins' tightly regulated interaction could mediate cell adhesion between brain cells.

Abnormalities of retinal metabolism in diabetes and experimental galactosemia. VII. Effect of long-term administration of antioxidants on the development of retinopathy

Antioxidants were administered to diabetic rats and experimentally galactosemic rats to evaluate the ability of these agents to inhibit the development of diabetic retinopathy. Alloxan diabetic rats and nondiabetic rats that were fed 30% galactose randomly received standard diets or the diets supplemented with ascorbic acid and alpha-tocopherol (vitamins C+E diet) or a more comprehensive mixture of antioxidants (multi-antioxidant diet), including Trolox, alpha-tocopherol, N-acetyl cysteine, ascorbic acid, beta-carotene, and selenium. Diabetes or galactose feeding of at least 12 months resulted in pericyte loss, acellular capillaries, and basement membrane thickening. Compared with diabetic controls, the development of acellular capillaries was inhibited by 50% (P < 0.05) in diabetic rats that received supplemental vitamins C+E, and the number of pericyte ghosts tended to be reduced. The vitamins C+E supplement had no beneficial effect in galactosemic rats, but these rats consumed only approximately half as much of the antioxidants as the diabetic rats. The multi-antioxidant diet significantly inhibited ( approximately 55-65%) formation of both pericyte ghosts and acellular capillaries in diabetic rats and galactosemic rats (P < 0.05 vs. controls), without affecting the severity of hyperglycemia. Parameters of retinal oxidative stress, protein kinase C activity, and nitric oxides remained elevated for at least 1 year of hyperglycemia, and these abnormalities were normalized by multi-antioxidant therapy. Thus, long-term administration of antioxidants can inhibit the development of the early stages of diabetic retinopathy, and the mechanism by which this action occurs warrants further investigation. Supplementation with antioxidants can offer an achievable and inexpensive adjunct therapy to help inhibit the development of retinopathy in diabetes.

Polyoxometalate HIV-1 protease inhibitors. A new mode of protease inhibition

Nb-containing polyoxometalates (POMs) of the Wells-Dawson class inhibit HIV-1 protease (HIV-1P) by a new mode based on kinetics, binding, and molecular modeling studies. Reaction of alpha(1)-K(9)Li[P(2)W(17)O(61)] or alpha(2)-K(10)[P(2)W(17)O(61)] with aqueous H(2)O(2) solutions of K(7)H[Nb(6)O(19)] followed by treatment with HCl and KCl and then crystallization affords the complexes alpha(1)-K(7)[P(2)W(17)(NbO(2))O(61)] (alpha(1)()1) and alpha(2)-K(7)[P(2)W(17)(NbO(2))O(61)] (alpha(2)()1) in 63 and 86% isolated yields, respectively. Thermolysis of the crude peroxoniobium compounds (72-96 h in refluxing H(2)O) prior to treatment with KCl converts the peroxoniobium compounds to the corresponding polyoxometalates (POMs), alpha(1)-K(7)[P(2)W(17)NbO(62)] (alpha(1)()2) and alpha(2)-K(7)[P(2)W(17)NbO(62)] (alpha(2)()2), in moderate yields (66 and 52%, respectively). The identity and high purity of all four compounds were confirmed by (31)P NMR and (183)W NMR. The acid-induced dimerization of the oxo complexes differentiates sterically between the cap (alpha(2)) site and the belt (alpha(1)) site in the Wells-Dawson structure (alpha(2)()2 dimerizes in high yield; alpha(1)()2 does not). All four POMs exhibit high activity in cell culture against HIV-1 (EC(50) values of 0.17-0.83 microM), are minimally toxic (IC(50) values of 50 to >100 microM), and selectively inhibit purified HIV-1 protease (HIV-1P) (IC(50) values for alpha(1)()1, alpha(2)()1, alpha(1)()2, and alpha(2)()2 of 2.0, 1.2, 1.5, and 1.8 microM, respectively). Thus, theoretical, binding, and kinetics studies of the POM/HIV-1P interaction(s) were conducted. Parameters for [P(2)W(17)NbO(62)](7)(-) were determined for the Kollman all-atom (KAA) force field in Sybyl 6.2. Charges for the POM were obtained from natural population analysis (NPA) at the HF/LANL2DZ level of theory. AutoDock 2.2 was used to explore possible binding locations for the POM with HIV-1P. These computational studies strongly suggest that the POMs function not by binding to the active site of HIV-1P, the mode of inhibition of all other HIV-1P protease inhibitors, but by binding to a cationic pocket on the "hinge" region of the flaps covering the active site (2 POMs and cationic pockets per active homodimer of HIV-1P). The kinetics and binding studies, conducted after the molecular modeling, are both in remarkable agreement with the modeling results: 2 POMs bind per HIV-1P homodimer with high affinities (K(i) = 1.1 +/- 0.5 and 4.1 +/- 1.8 nM in 0.1 and 1.0 M NaCl, respectively) and inhibition is noncompetitive (k(cat) but not K(m) is affected by the POM concentration).

Crystal structure of human cytosolic phospholipase A2 reveals a novel topology and catalytic mechanism

Cytosolic phospholipase A2 initiates the biosynthesis of prostaglandins, leukotrienes, and platelet-activating factor (PAF), mediators of the pathophysiology of asthma and arthritis. Here, we report the X-ray crystal structure of human cPLA2 at 2.5 A. cPLA2 consists of an N-terminal calcium-dependent lipid-binding/C2 domain and a catalytic unit whose topology is distinct from that of other lipases. An unusual Ser-Asp dyad located in a deep cleft at the center of a predominantly hydrophobic funnel selectively cleaves arachidonyl phospholipids. The structure reveals a flexible lid that must move to allow substrate access to the active site, thus explaining the interfacial activation of this important lipase.

Rational design of allosteric ribozymes

BACKGROUND

Efficient operation of cellular processes relies on the strict control that each cell exerts over its metabolic pathways. Some protein enzymes are subject to allosteric regulation, in which binding sites located apart from the enzyme's active site can specifically recognize effector molecules and alter the catalytic rate of the enzyme via conformational changes. Although RNA also performs chemical reactions, no ribozymes are known to operate as true allosteric enzymes in biological systems. It has recently been established that small-molecule receptors can readily be made of RNA, as demonstrated by the in vitro selection of various RNA aptamers that can specifically bind corresponding ligand molecules. We set out to examine whether the catalytic activity of an existing ribozyme could be brought under the control of an effector molecule by designing conjoined aptamer-ribozyme complexes.

RESULTS

By joining an ATP-binding RNA to a self-cleaving ribozyme, we have created the first example of an allosteric ribozyme that has a catalytic rate that can be controlled by ATP. A 180-fold reduction in rate is observed upon addition of either adenosine or ATP, but no inhibition is detected in the presence of dATP or other nucleoside triphosphates. Mutations in the aptamer domain that are expected to eliminate ATP binding or that increase the distance between aptamer and ribozyme domains result in a loss of ATP-specific allosteric control. Using a similar design approach, allosteric hammerhead ribozymes that are activated in the presence of ATP were created and another ribozyme that can be controlled by theophylline was created.

CONCLUSIONS

The catalytic features of these conjoined aptamer-ribozyme constructs demonstrate that catalytic RNAs can also be subject to allosteric regulation-a key feature of certain protein enzymes. Moreover, by using simple rational design strategies, it is now possible to engineer new catalytic polynucleotides which have rates that can be tightly and specifically controlled by small effector molecules.

PRMT 3, a type I protein arginine N-methyltransferase that differs from PRMT1 in its oligomerization, subcellular localization, substrate specificity, and regulation

Methylation is one of the many post-translational modifications that modulate protein function. Although asymmetric NG,NG-dimethylation of arginine residues in glycine-arginine-rich domains of eucaryotic proteins, catalyzed by type I protein arginine N-methyltransferases (PRMT), has been known for some time, members of this enzyme class have only recently been cloned. The first example of this type of enzyme, designated PRMT1, cloned because of its ability to interact with the mammalian TIS21 immediate-early protein, was then shown to have protein arginine methyltransferase activity. We have now isolated rat and human cDNA orthologues that encode proteins with substantial sequence similarity to PRMT1. A recombinant glutathione S-transferase (GST) fusion product of this new rat protein, named PRMT3, asymmetrically dimethylates arginine residues present both in the designed substrate GST-GAR and in substrate proteins present in hypomethylated extracts of a yeast rmt1 mutant that lacks type I arginine methyltransferase activity; PRMT3 is thus a functional type I protein arginine N-methyltransferase. However, rat PRMT1 and PRMT3 glutathione S-transferase fusion proteins have distinct enzyme specificities for substrates present in both hypomethylated rmt1 yeast extract and hypomethylated RAT1 embryo cell extract. TIS21 protein modulates the enzymatic activity of recombinant GST-PRMT1 fusion protein but not the activity of GST-PRMT3. Western blot analysis of gel filtration fractions suggests that PRMT3 is present as a monomer in RAT1 cell extracts. In contrast, PRMT1 is present in an oligomeric complex. Immunofluorescence analysis localized PRMT1 predominantly to the nucleus of RAT1 cells. In contrast, PRMT3 is predominantly cytoplasmic.

Susceptibility mapping as a means to visualize veins and quantify oxygen saturation

PURPOSE

To create an orientation-independent, 3D reconstruction of the veins in the brain using susceptibility mapping.

MATERIALS AND METHODS

High-resolution, high-pass filtered phase images usually used for susceptibility weighted imaging (SWI) were used as a source for local magnetic field behavior. These images were subsequently postprocessed using an inverse procedure to generate susceptibility maps of the veins. Regularization and interpolation of the data in k-space of the phase images were used to reduce reconstruction artifacts. To understand the effects of artifacts, and to fine-tune the methodology, simulations of blood vessels were performed with and without noise.

RESULTS

With sufficient resolution, major veins in the brain could be visualized with this approach. The usual geometry-dependent phase dipole effects are removed by this processing, leaving basically images of the veins. Different sized vessels show a different level of contrast depending on their partial volume effects. Vessels that are 8 mm or 16 mm in size show quantitative values expected for normal oxygen saturation levels. Smaller vessels show smaller values due to errors in the methodology and due to partial volume effects. Larger vessels show a bias toward a reduced susceptibility approaching 90% of the expected value. Limitations of the method and artifacts related to different sources of errors are demonstrated.

CONCLUSION

Susceptibility maps can successfully create venograms of the brain with varying levels of contrast-to-noise depending on the size of the vessel. Partial volume effects render this approach more useful as an imaging tool or a visualization tool, although certain larger vessels have measured susceptibilities close to expected values associated with normal blood oxygen saturation levels.

A novel cytosolic calcium-independent phospholipase A2 contains eight ankyrin motifs

We report the purification, molecular cloning, and expression of a novel cytosolic calcium-independent phospholipase A2 (iPLA2) from Chinese hamster ovary cells, which lacks extended homology to other phospholipases. iPLA2 is an 85-kDa protein that exists as a multimeric complex of 270-350 kDa with a specific activity of 1 micromol/min/mg. The full-length cDNA clone encodes a 752-amino acid cytoplasmic protein with one lipase motif (GXS465XG) and eight ankyrin repeats. Expression of the cDNA in mammalian cells generates an active 85-kDa protein. Mutagenesis studies show that Ser465 and the ankyrin repeats are required for activity. We demonstrate that iPLA2 selectively hydrolyzes the sn-2 over sn-1 fatty acid by 5-fold for 1,2-dipalmitoyl phosphatidylcholine in a mixed micelle. Moreover, we found the fatty acid preference at the sn-2 position to be highly dependent upon substrate presentation. However, iPLA2 does have a marked preference for 1,2-dipalmitoyl phosphatidic acid presented in a vesicle, generating the lipid second messenger lysophosphatidic acid. Finally the enzyme is able to hydrolyze the acetyl moiety at the sn-2 position of platelet-activating factor.

Neurovascular Protection Reduces Early Brain Injury After Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Cell death, especially apoptosis, occurred in brain tissues after subarachnoid hemorrhage (SAH). We examined the relationships between apoptosis and the disruption of blood-brain barrier (BBB), brain edema, and mortality in an established endovascular perforation model in male Sprague-Dawley rats.

METHODS

A pan-caspase inhibitor (z-VAD-FMK) was administered intraperitoneally at 1 hour before and 6 hours after SAH. Expression of caspase-3 and positive TUNEL was examined as markers for apoptosis.

RESULTS

Apoptosis occurred mostly in cerebral endothelial cells, partially in neurons in the hippocampus, and to a lesser degree in the cerebral cortex. Accordingly, increased BBB permeability and brain water content were observed, accompanied by neurological deficit and a high mortality at 24 hours after SAH. z-VAD-FMK suppressed TUNEL and caspase-3 staining in endothelial cells, decreased caspase-3 activation, reduced BBB permeability, relieved vasospasm, abolished brain edema, and improved neurological outcome.

CONCLUSIONS

The major effect of z-VAD-FMK on early brain injury after SAH was probably neurovascular protection of cerebral endothelial cells, which results in less damage on BBB.

Evolution in the structure and function of aspartic proteases

Aspartic proteases (EC3.4.23) are a group of proteolytic enzymes of the pepsin family that share the same catalytic apparatus and usually function in acid solutions. This latter aspect limits the function of aspartic proteases to some specific locations in different organisms; thus the occurrence of aspartic proteases is less abundant than other groups of proteases, such as serine proteases. The best known sources of aspartic proteases are stomach (for pepsin, gastricsin, and chymosin), lysosomes (for cathepsins D and E), kidney (for renin), yeast granules, and fungi (for secreted proteases such as rhizopuspepsin, penicillopepsin, and endothiapepsin). These aspartic proteases have been extensively studied for their structure and function relationships and have been the topics of several reviews or monographs (Tang: Acid Proteases, Structure, Function and Biology. New York: Plenum Press, 1977; Tang: J Mol Cell Biochem 26:93-109, 1979; Kostka: Aspartic Proteinases and Their Inhibitors. Berlin: Walter de Gruyter, 1985). All mammalian aspartic proteases are synthesized as zymogens and are subsequently activated to active proteases. Although a zymogen for a fungal aspartic protease has not been found, the cDNA structure of rhizopuspepsin suggests the presence of a "pro" enzyme (Wong et al: Fed Proc 44:2725, 1985). It is probable that other fungal aspartic proteases are also synthesized as zymogens. It is the aim of this article to summarize the major models of structure-function relationships of aspartic proteases and their zymogens with emphasis on more recent findings. Attempts will also be made to relate these models to other aspartic proteases.

Evidence for two types of spatial representations: Hemispheric specialization for categorical and coordinate relations

Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments--on/off, left/right, and above/below--faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance--in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)--faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice.