Copper mediates dityrosine cross-linking of Alzheimer's amyloid-beta

We have previously reported that amyloid Abeta, the major component of senile plaques in Alzheimer's disease (AD), binds Cu with high affinity via histidine and tyrosine residues [Atwood, C. S., et al. (1998) J. Biol. Chem. 273, 12817-12826; Atwood, C. S., et al. (2000) J. Neurochem. 75, 1219-1233] and produces H(2)O(2) by catalyzing the reduction of Cu(II) or Fe(III) [Huang, X., et al. (1999) Biochemistry 38, 7609-7616; Huang, X., et al. (1999) J. Biol. Chem. 274, 37111-37116]. Incubation with Cu induces the SDS-resistant oligomerization of Abeta [Atwood, C. S., et al. (2000) J. Neurochem. 75, 1219-1233], a feature characteristic of neurotoxic soluble Abeta extracted from the AD brain. Since residues coordinating Cu are most vulnerable to oxidation, we investigated whether modifications of these residues were responsible for Abeta cross-linking. SDS-resistant oligomerization of Abeta caused by incubation with Cu was found to induce a fluorescence signal characteristic of tyrosine cross-linking. Using ESI-MS and a dityrosine specific antibody, we confirmed that Cu(II) (at concentrations lower than that associated with amyloid plaques) induces the generation of dityrosine-cross-linked, SDS-resistant oligomers of human, but not rat, Abeta peptides. The addition of H2O2 strongly promoted Cu-induced dityrosine cross-linking of Abeta1-28, Abeta1-40, and Abeta1-42, suggesting that the oxidative coupling is initiated by interaction of H2O2 with a Cu(II) tyrosinate. The dityrosine modification is significant since it is highly resistant to proteolysis and is known to play a role in increasing structural strength. Given the elevated concentration of Cu in senile plaques, our results suggest that Cu interactions with Abeta could be responsible for causing the covalent cross-linking of Abeta in these structures.     

Structural characterization of the O-chain polysaccharide isolated from Bordetella avium ATCC 5086: variation on a theme(1)

The O-chain polysaccharide (O-PS) of Bordetella avium was isolated from the lipopolysaccharide by mild acid hydrolysis to remove the lipid A, followed by hydrofluorolysis to remove the lipopolysaccharide core oligosaccharide leaving a residual O-PS for structural analysis. High resolution (1)H and (13)C NMR and MALDI studies showed the O-chain to be a polymer composed of 1,4-linked 2-acetamidino-3-[3-hydroxybutanamido]-2,3-dideoxy-beta-D-glucopyranosyluronic acid residues.     

Translational regulation of the plant S-adenosylmethionine decarboxylase

It is becoming apparent that control of protein synthesis by metabolites is more common than previously thought. Much of that control is exerted at the level of initiation of mRNA translation, orchestrated by upstream open reading frames (uORFs) and RNA secondary structure. S-Adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in polyamine biosynthesis and both mammalian and plant AdoMetDCs are translationally regulated by uORFs in response to polyamine levels by distinct mechanisms.     

Mechanical loading: biphasic osteocyte survival and targeting of osteoclasts for bone destruction in rat cortical bone

Bone isremoved or replaced in defined locations by targeting osteoclasts andosteoblasts in response to its local history of mechanical loading.There is increasing evidence that osteocytes modulate this targeting bytheir apoptosis, which is associated with locally increasedbone resorption. To investigate the role of osteocytes in the controlof loading-related modeling or remodeling, we studied the effects onosteocyte viability of short periods of mechanical loading applied tothe ulnae of rats. Loading, which produced peak compressive strains of0.003 or 0.004, was associated with a 78% reduction in theresorption surface at the midshaft. The same loading regimen resultedin a 40% relative reduction in osteocyte apoptosis at the samesite 3 days after loading compared with the contralateral side(P = 0.01). The proportion of osteocytes that wereapoptotic was inversely related to the estimated local strain(P < 0.02). In contrast, a single short period ofloading resulting in strains of 0.008 engendered both tissuemicrodamage and subsequent bone remodeling and was associated with aneightfold increase in the proportion of apoptotic osteocytes(P = 0.02) at 7 days. This increase in osteocyteapoptosis was transient and preceded both intracorticalremodeling and death of half of the osteocytes (P < 0.01). The data suggest that osteocytes might use their U-shapedsurvival response to strain as a mechanism to influence boneremodeling. We hypothesize that this relationship reflects a causalmechanism by which osteocyte apoptosis regulates bone'sstructural architecture.

     

Expressed murine and human CDR-H3 intervals of equal length exhibit distinct repertoires that differ in their amino acid composition and predicted range of structures

Immunoglobulin junctional diversity is concentrated in the third complementarity-determining region of the heavy chain (CDR-H3), which often plays a dominant role in antigen binding. The range of CDR-H3 lengths in mouse is shorter than in human, and thus the murine repertoire could be presumed to be a subset of the human one. To test this presumption, we analyzed 4751 human and 2170 murine unique, functional, published CDR-H3 intervals. Although tyrosine, glycine, and serine were found to predominate in both species, the human sequences contained fewer tyrosine residues, more proline residues, and more hydrophobic residues (p<0.001, respectively). While changes in amino acid utilization as a function of CDR-H3 length followed similar trends in both species, murine and human CDR-H3 intervals of identical length were found to differ from each other. These differences reflect both divergence of germline diversity and joining gene sequence and somatic selection. Together, these factors promote the production of a rather uniform repertoire in mice of tyrosine-enriched CDR-H3 loops with stabilized hydrogen bond-ladders versus a much more diverse repertoire in human that contains CDR-H3 loops sculpted by the presence of intra-chain disulfide bonds due to germline-encoded cysteine residues as well as the enhanced presence of somatically generated proline residues that preclude hydrogen bond ladder formation. Thus, despite the presumed need to recognize a similar range of antigen epitopes, the murine CDR-H3 repertoire is clearly distinct from its human counterpart in its amino acid composition and its predicted range of structures. These findings represent a benchmark to which CDR-H3 repertoires can be compared to better characterize and understand the shaping of the CDR-H3 repertoire over evolution and during immune responses. This information may also be useful for the design of species-specific CDR-H3 sequences in synthetic antibody libraries.     

Founder control and coexistence in a simple model of asymmetric competition for light

Size asymmetry in plant light acquisition complicates predictions of competitive outcomes in light-limited communities. We present a mathematically tractable model of asymmetric competition for light and discuss its implications for predicting outcomes of competition during establishment in two-, three-, and many-species communities. In contrast to the resource-reduction model of symmetric competition for a single resource, the model we present predicts that outcomes of asymmetric competition for light will sometimes depend on the timing of establishment and the consequent hierarchy among species in canopy position. Competitive outcomes in the model depend on the minimum light requirements (L(c)) and self-shading of species lower in the canopy compared to the light available (L(out)(*)) beneath species higher in the canopy. Succession progresses towards species with decreasing values for L(c), but arrested successions occur when initial dominants have relatively high values for L(c) but low values for L(out)(*), leading to founder control. A theoretically limitless number of species may coexist in competition for light when dominance is founder controlled. These model predictions have implications for an array of applied ecological questions, including methods to control invasive species in light-limited restored ecosystems.     

Comparative immunogenicity in rhesus monkeys of DNA plasmid,recombinant vaccinia virus,and replication-defective adenovirus vectors expressing a human immunodeficiency virus type 1 gag gene

Cellular immune responses, particularly those associated with CD3⁺ CD8⁺ cytotoxic T lymphocytes (CTL), play a primary role in controlling viral infection, including persistent infection with human immunodeficiency virus type 1 (HIV-1). Accordingly, recent HIV-1 vaccine research efforts have focused on establishing the optimal means of eliciting such antiviral CTL immune responses. We evaluated several DNA vaccine formulations, a modified vaccinia virus Ankara vector, and a replication-defective adenovirus serotype 5 (Ad5) vector, each expressing the same codon-optimized HIV-1 gag gene for immunogenicity in rhesus monkeys. The DNA vaccines were formulated with and without one of two chemical adjuvants (aluminum phosphate and CRL1005). The Ad5-gag vector was the most effective in eliciting anti-Gag CTL. The vaccine produced both CD4⁺ and CD8⁺ T-cell responses, with the latter consistently being the dominant component. To determine the effect of existing antiadenovirus immunity on Ad5-gag-induced immune responses, monkeys were exposed to adenovirus subtype 5 that did not encode antigen prior to immunization with Ad5-gag. The resulting anti-Gag T-cell responses were attenuated but not abolished. Regimens that involved priming with different DNA vaccine formulations followed by boosting with the adenovirus vector were also compared. Of the formulations tested, the DNA-CRL1005 vaccine primed T-cell responses most effectively and provided the best overall immune responses after boosting with Ad5-gag. These results are suggestive of an immunization strategy for humans that are centered on use of the adenovirus vector and in which existing adenovirus immunity may be overcome by combined immunization with adjuvanted DNA and adenovirus vector boosting.     

Biological degradation of coral framework in a turbid lagoon environment,Discovery Bay,north Jamaica

The potentially negative effects of increased sedimentation on corals are well documented, whereas, the impacts upon early diagenetic processes, such as bioerosion, remain poorly understood. This study examined macroboring through image analysis of coral slabs from two high sedimentation and turbid reefs, Columbus Park and Red Buoy, within Discovery Bay, north Jamaica. Infestation of coral framework by macroborers was significant at both Columbus Park and Red Buoy for all depth zones sampled: 0–8 m (6.5 versus 8.3%), 8–16 m (11.4 versus 10.7%), and 16–25 m (6.2 versus 18.5%), with only the deepest zone significantly different (P<0.001). Bioeroding communities exhibit a shift from mainly sponge-dominated (>90%) assemblages in clear-water settings towards a greater relative importance of worms (up to 17.2%) and bivalves (up to 40.5%) with increasing sedimentation. The high infestation levels of the bivalve Lithophaga spp. offset the reduced sponge bioerosion. As a result, macroboring infestation levels are comparable to those reported from adjacent clear-water reef sites. This study indicates that macroboring of coral framework continues under environmental conditions previously inferred to be detrimental to coral growth and survival.