Seaduck engineers in the Arctic Archipelago: nesting eiders deliver marine nutrients and transform the chemistry of island soils, plants, and ponds.

Seabirds are thought to provide ecological services such as the movement of nutrients between marine and terrestrial ecosystems, which may be especially critical to productivity and diversity in nutrient-poor environments. Most Arctic ecosystems are unaffected by local human impacts and are naturally nutrient poor and especially sensitive to warming. Here, we assessed the effects of nesting common eider ducks (Somateria mollissima) on soil, vegetation, and pond sediments on island archipelagoes in Hudson Strait between Nunavut and Québec, Canada. Soil, moss, and pond sediments were significantly higher in nitrogen on islands with large numbers of nesting eiders compared to sites with no nesting birds. The highest concentrations of nitrogen in soils and moss occurred at the margins of ponds on eider islands, which correspond to the areas of highest eider use. δ15N and δ34S values in soils, moss, and sediments indicated substantial marine-derived organic matter inputs at the higher nutrient sites. We propose that by foraging on coastal marine benthic invertebrates and returning to islands to nest, eider ducks bio-transport and concentrate marine-derived nutrients to their colony islands, fertilizing Arctic island ecosystems in the process. As common eiders nest on thousands of low to mid-latitude islands throughout the circumpolar Arctic, these nutrient inputs likely dramatically affect biota and ecosystem functioning throughout the tundra biome.

Generation of a large combinatorial library of the immunoglobulin repertoire in phage lambda.

A novel bacteriophage lambda vector system was used to express in Escherichia coli a combinatorial library of Fab fragments of the mouse antibody repertoire. The system allows rapid and easy identification of monoclonal Fab fragments in a form suitable for genetic manipulation. It was possible to generate, in 2 weeks, large numbers of monoclonal Fab fragments against a transition state analog hapten. The methods described may supersede present-day hybridoma technology and facilitate the production of catalytic and other antibodies.

Metalloantibodies.

A metalloantibody has been constructed with a coordination site for metals in the antigen binding pocket. The Zn(II) binding site from carbonic anhydrase B was used as a model. Three histidine residues have been placed in the light chain complementarity determining regions of a single chain antibody molecule. In contrast to the native protein, the mutant displayed metal-dependent fluorescence-quenching behavior. This response was interpreted as evidence for metal binding in the three-histidine site with relative affinities in the order Cu(II) greater than Zn(II) greater than Cd(II). The presence of metal cofactors in immunoglobulins should facilitate antibody catalysis of redox and hydrolytic reactions.

Anatomical patterns of colonization of pets with staphylococcal species in homes of people with methicillin-resistant Staphylococcus aureus (MRSA) skin or soft tissue infection (SSTI).

Methicillin-resistant strains of Staphylococcus aureus (MRSA), Staphylococcus pseudintermedius (MRSP), and other pathogenic staphylococci can cause infections in companion animals and humans. Identification of colonized animals is fundamental to research and practice needs, but harmonized methods have not yet been established. To establish the optimal anatomic site for the recovery of methicillin-resistant coagulase positive staphylococci (CPS), survey data and swabs were collected from 196 pets (dogs, cats, reptiles, birds, fish and pocket pets) that lived in households with an MRSA-infected person. Using broth-enrichment culture and PCR for speciation, S. aureus was identified in 27 of 179 (15%) pets sampled at baseline and 19 of 125 (15%) pets sampled at a three-month follow-up home visit. S. pseudintermedius was isolated from 33 of 179 (18%) pets sampled at baseline and 21 of 125 (17%) of pets sampled at follow-up. The baseline MRSA and MRSP prevalence was 8% and 1% respectively from 145 mammalian pets. The follow-up MRSA and MRSP prevalence was 7% and <1% respectively from 95 mammalian pets. The mouth was the most sensitive single site sampled for isolation of S. aureus and S. pseudintermedius in mammals. In a subset of pets, from which all available isolates were identified, dual carriage of S. aureus and S. pseudintermedius was 22% at baseline and 11% at follow-up. These results identify the mouth as the most sensitive site to screen for pathogenic staphylococci and suggest that it should be included in sampling protocols.

Comparison of dysmorphic erythrocytes with other urinary sediment parameters of renal bleeding.

Dysmorphic erythrocytes have been described in the urine sediment of patients with renal parenchymal bleeding. This study compares the prevalence of dysmorphic erythrocytes in 5,128 urine specimens with blood, erythrocytic, or fibrin casts, proteinuria, and significant numbers of exfoliated renal tubular cells (RTCs). Of the 510 samples containing pathologic casts, 15% had dysmorphic erythrocytes, 60% had proteinuria, 71% had RTCs, and 12% had no other urinalysis abnormality. Of the 186 samples containing dysmorphic erythrocytes, 55% had pathologic casts, 42% had proteinuria, 71% had RTCs, and 13% had no other abnormality. Renal hematuria can best be evaluated by examination of all four of these urinalysis abnormalities rather than using a single entity for diagnosis. Patients with urinalysis evidence of renal hematuria should be evaluated further for renal disease rather than lower urinary tract disorders.

Tritylase antibodies.

We have used a tris(4-methoxyphenyl)-phosphonium compound as a hapten to elicit catalytic antibodies that selectively remove trityl protecting groups at neutral pH. One antibody, 37C4, was characterized kinetically with a number of trityl substrates. The rate enhancement was consistently near 200; the Km was approximately 30 microM for the methoxytrityl substrates. Compounds with no methoxy substituents on the trityl group were not hydrolysed by the antibody. No decrease in the rate of reaction was detected through 21 turnovers, which suggests that the presumptive trityl cation formed during the cleavage reaction does not alkylate the antibody binding pocket. The rates of the background and antibody-catalysed reactions both increase logarithmically with decreasing pH, implying that general acid catalysis is not involved: further studies will test this assumption. The favoured mechanism for the catalytic activity of antibody 37C4 is charge complementarity in the binding site stabilizing a positively charged intermediate(s) in the cleavage reaction. The coding sequence for 37C4 is being cloned into a phage lambda vector in preparation for site-directed mutagenesis to improve the catalytic efficiency of the antibody.

Gene synthesis, expression, and mutagenesis of the blue copper proteins azurin and plastocyanin.

Genes for the blue copper proteins Populus nigra var. italica plastocyanin and Pseudomonas aeruginosa azurin have been constructed by a stepwise procedure. The leader sequence for azurin has been placed before the genes directing plastocyanin and azurin transport to the periplasmic space when the genes are expressed in Escherichia coli. Site-saturation mutagenesis has been used to alter two copper-binding residues of azurin (Met-121 and His-46) and Met-92 of plastocyanin. While the plastocyanin mutants do not appear to bind copper, the azurin variants all bind copper and show characteristic type I blue copper centers. In particular, the electronic spectra reflect the dominance of the charge transfer interaction between copper and the thiolate of Cys-112, being relatively insensitive to changes in Met-121 or His-46. In contrast, removal of Met-121 appreciably alters the EPR spectra of the mutants, although, to a first order, the spectra of all mutants are themselves similar, suggesting a more distorted geometry around copper in the mutants than in the wild type.

Antibody remodeling: a general solution to the design of a metal-coordination site in an antibody binding pocket.

To develop a general approach to designing cofactor-binding sites for catalytic antibodies, we characterized structural patterns in the binding sites of antibodies and zinc enzymes. Superposition of eight sets of antibody light- and heavy-chain variable domains identified structurally conserved sites within the sequence-variable complementarity determining regions. The pattern for catalytic zinc sites included two ligands close in sequence, a sequence-distant ligand, and a main-chain hydrogen bond joining two ligands. In both the light- and heavy-chain variable domains, the stereochemistry of five structurally conserved sites general to all known antibody structures matched that of the zinc ligands of carbonic anhydrase: three residues on two hydrogen-bonded antiparallel beta-strands. For one such general site, an antibody model replacing residue 34 on the first complementarity determining region of the light chain (L1) and residues 89 and 91 on the third complementarity determining region of the light chain (L3) with histidine ligands formed a zinc-binding site with an open coordination position at the bottom of the antibody binding pocket. For the anti-fluorescein antibody 4-4-20, this L1-L3 site placed the zinc ion about 4 A from the bound fluorescein, an indicator for metal binding. This predicted zinc-binding mutant was created in the single-chain variable domain construct, expressed, and found by fluorescence quenching to bind metal ion with an affinity constant of 10(6) M-1. Thus, our template-based multisite design proved successful for remodeling an antibody to contain a cofactor-binding site, without requiring further mutagenesis and screening. Combination of a specific light or heavy chain containing a catalytic metal site with a library of complementary chains raised to potential substrates or transition state analogs should greatly improve the production of catalytic antibodies with desired activities and specificities.