Biolayer interferometry predicts ELISA performance of monoclonal antibody pairs for Plasmodium falciparum histidine-rich protein 2

Predicting antibody pair performance in a sandwich format streamlines development of antibody-based diagnostics and laboratory research tools, such as enzyme-linked immunosorbent assays (ELISAs) and lateral flow immunoassays (LFAs). We have evaluated panels of monoclonal antibodies against the malarial parasite biomarker Plasmodium falciparum histidine rich protein 2 (HRP2), including 9 new monoclonal antibodies, using biolayer interferometry (BLI) and screened antibody pairs in a checkerboard ELISA. This study showed BLI predicts antibody pair ELISA performance for HRP2. Pairs that included capture antibodies with low off-rate constants and detection antibodies with high on-rate constants performed best in an ELISA format.

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Kinetic parameters of 15 anti-HRP2 antibodies are measured by biolayer interferometry.

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Kinetic constants are compared to a checkerboard ELISA of 225 antibody pairs.

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Biolayer interferometry predicts antibody pair performance for HRP2 ELISA.

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Capture mAbs with low k_off and detection mAbs with high k_on are best in HRP2 ELISA.

Barley arabinoxylan arabinofuranohydrolases: purification, characterization and determination of primary structures from cDNA clones

A family 51 arabinoxylan arabinofuranohydrolase, designated AXAH-I, has been purified from extracts of 7-day-old barley (Hordeum vulgare L.) seedlings by fractional precipitation with (NH(4))(2)SO(4) and ion-exchange chromatography. The enzyme has an apparent molecular mass of 65 kDa and releases L-arabinose from cereal cell wall arabinoxylans with a pH optimum of 4.3, a catalytic rate constant (k(cat)) of 6.9 s(-1) and a catalytic efficiency factor (k(cat)/K(m)) of 0.76 (ml x s(-1) x mg(-1)). Whereas the hydrolysis of alpha-L-arabinofuranosyl residues linked to C(O)3 of backbone (1-->4)-beta-xylosyl residues proceeds at the fastest rate, alpha-L-arabinofuranosyl residues on doubly substituted xylosyl residues are also hydrolysed, at lower rates. A near full-length cDNA encoding barley AXAH-I indicates that the mature enzyme consists of 626 amino acid residues and has a calculated pI of 4.8. A second cDNA, which is 81% identical with that encoding AXAH-I, encodes another barley AXAH, which has been designated AXAH-II. The barley AXAHs are likely to have key roles in wall metabolism in cereals and other members of the Poaceae. Thus the enzymes could participate in the modification of the fine structure of arabinoxylan during wall deposition, maturation or expansion, or in wall turnover and the hydrolysis of arabinoxylans in germinated grain.

Substrate recognition by the Lyn protein-tyrosine kinase. NMR structure of the immunoreceptor tyrosine-based activation motif signaling region of the B cell antigen receptor

The immunoreceptor tyrosine-based activation motif (ITAM) plays a central role in transmembrane signal transduction in hematopoietic cells by mediating responses leading to proliferation and differentiation. An initial signaling event following activation of the B cell antigen receptor is phosphorylation of the CD79a (Ig-alpha) ITAM by Lyn, a Src family protein-tyrosine kinase. To elucidate the structural basis for recognition between the ITAM substrate and activated Lyn kinase, the structure of an ITAM-derived peptide bound to Lyn was determined using exchange-transferred nuclear Overhauser NMR spectroscopy. The bound substrate structure has an irregular helix-like character. Docking based on the NMR data into the active site of the closely related Lck kinase strongly favors ITAM binding in an orientation similar to binding of cyclic AMP-dependent protein kinase rather than that of insulin receptor tyrosine kinase. The model of the complex provides a rationale for conserved ITAM residues, substrate specificity, and suggests that substrate binds only the active conformation of the Src family tyrosine kinase, unlike the ATP cofactor, which can bind the inactive form.

Virus-induced silencing of a plant cellulose synthase gene

Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infected with one group of cDNAs had much shorter internode lengths, small leaves, and a "dwarf" phenotype. Consistent with a loss of cell wall cellulose, abnormally large and in many cases spherical cells ballooned from the undersurfaces of leaves, particularly in regions adjacent to vascular tissues. Linkage analyses of wall polysaccharides prepared from infected leaves revealed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected plants. The decrease in cellulose content in cell walls was offset by an increase in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from approximately 50 to approximately 33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellulose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellulose synthase genes.

Virus-induced silencing of a plant cellulose synthase gene

Specific cDNA fragments corresponding to putative cellulose synthase genes (CesA) were inserted into potato virus X vectors for functional analysis in Nicotiana benthamiana by using virus-induced gene silencing. Plants infected with one group of cDNAs had much shorter internode lengths, small leaves, and a "dwarf" phenotype. Consistent with a loss of cell wall cellulose, abnormally large and in many cases spherical cells ballooned from the undersurfaces of leaves, particularly in regions adjacent to vascular tissues. Linkage analyses of wall polysaccharides prepared from infected leaves revealed a 25% decrease in cellulose content. Transcript levels for at least one member of the CesA cellulose synthase gene family were lower in infected plants. The decrease in cellulose content in cell walls was offset by an increase in homogalacturonan, in which the degree of esterification of carboxyl groups decreased from approximately 50 to approximately 33%. The results suggest that feedback loops interconnect the cellular machinery controlling cellulose and pectin biosynthesis. On the basis of the phenotypic features of the infected plants, changes in wall composition, and the reduced abundance of CesA mRNA, we concluded that the cDNA fragments silenced one or more cellulose synthase genes.

A single limit dextrinase gene is expressed both in the developing endosperm and in germinated grains of barley

The single gene encoding limit dextrinase (pullulan 6-glucanohydrolase; EC 3.2.1.41) in barley (Hordeum vulgare) has 26 introns that range in size from 93 to 822 base pairs. The mature polypeptide encoded by the gene has 884 amino acid residues and a calculated molecular mass of 97,417 D. Limit dextrinase mRNA is abundant in gibberellic acid-treated aleurone layers and in germinated grain. Gibberellic acid response elements were found in the promoter region of the gene. These observations suggest that the enzyme participates in starch hydrolysis during endosperm mobilization in germinated grain. The mRNA encoding the enzyme is present at lower levels in the developing endosperm of immature grain, a location consistent with a role for limit dextrinase in starch synthesis. Enzyme activity was also detected in developing grain. The limit dextrinase has a presequence typical of transit peptides that target nascent polypeptides to amyloplasts, but this would not be expected to direct secretion of the mature enzyme from aleurone cells in germinated grain. It remains to be discovered how the enzyme is released from the aleurone and whether another enzyme, possibly of the isoamylase group, might be equally important for starch hydrolysis in germinated grain.

Molecular cloning of a cDNA encoding a (1-->4)-beta-mannan endohydrolase from the seeds of germinated tomato (Lycopersicon esculentum)

Mannose-containing polysaccharides are widely distributed in cell walls of higher plants. During endosperm mobilization in germinated tomato seeds (1-->4)-beta-mannan endohydrolases (EC 3.2.1.78) participate in the enzymic depolymerization of these cell wall polysaccharides. A cDNA encoding a (1-->4)-beta-mannanase from the endosperm of germinated tomato (Lycopersicon esculentum Mill.) seeds has been isolated and characterized. The amino acid sequence deduced from the 5'-region of the cDNA exactly matches the sequence of the 65 NH2-terminal amino acids determined directly from the purified enzyme. The mature enzyme consists of 346 amino acid residues, it has a calculated M(r) of 38,950 and an isoelectric point of 5.3. Overall, the enzyme exhibits only 28-30% sequence identity with fungal (1-->4)-beta-mannanases, but more highly conserved regions, which may represent catalytic and substrate-binding domains, can be identified. Based on classification of the tomato (1-->4)-beta-mannanase as a member of the family 5 group of glycosyl hydrolases, Glu-148 and Glu-265 would be expected to be the catalytic acid and the catalytic nucleophile, respectively. Southern hybridization analyses indicate that the enzyme is derived from a family of about four genes. Expression of the genes, as determined by the presence of mRNA transcripts in Northern hybridization analyses, occurs in the endosperm of germinated seeds; no transcripts are detected in hypocotyls, cotyledons, roots or leaves.

Starch branching enzymes belonging to distinct enzyme families are differentially expressed during pea embryo development

cDNA clones for two isoforms of starch branching enzyme (SBEI and SBEII) have been isolated from pea embryos and sequenced. The deduced amino acid sequences of pea SBEI and SBEII are closely related to starch branching enzymes of maize, rice, potato and cassava and a number of glycogen branching enzymes from yeast, mammals and several prokaryotic species. In comparison with SBEI, the deduced amino acid sequence of SBEII lacks a flexible domain at the N-terminus of the mature protein. This domain is also present in maize SBEII and rice SBEIII and resembles one previously reported for pea granule-bound starch synthase II (GBSSII). However, in each case it is missing from the other isoform of SBE from the same species. On the basis of this structural feature (which exists in some isoforms from both monocots and dicots) and other differences in sequence, SBEs from plants may be divided into two distinct enzyme families. There is strong evidence from our own and other work that the amylopectin products of the enzymes from these two families are qualitatively different. Pea SBEI and SBEII are differentially expressed during embryo development. SBEI is relatively highly expressed in young embryos whilst maximum expression of SBEII occurs in older embryos. The differential expression of isoforms which have distinct catalytic properties means that the contribution of each SBE isoform to starch biosynthesis changes during embryo development. Qualitative measurement of amylopectin from developing and maturing embryos confirms that the nature of amylopectin changes during pea embryo development and that this correlates with the differential expression of SBE isoforms.

Seizure of Eccentrically Loaded Journal Bearings and Sealing Rings

Thermal and elastic deformations are derived for a ring receiving heat input over a limited part of its inner circumference. This is applied to the problem of seizure of journal bearings or radial seals operating with dry or boundary lubricated contact. It is found that when the ratio of outer to inner radius for the ring is less than 1.715, seizure will not occur as a result of the mode of distortion studied. For thicker bearing/housing bodies there is always some load-speed combination which will lead to seizure, and this may occur in the range of common speeds and loads encountered in engineering applications.

Experimental Studies on Thermoelastic Effects in Hydrodynamically Lubricated Face Seals

Experiments are reported where face-seat specimens were operated hydrodynamically at conditions close to thermal equilibrium. Changes in surface waviness and mean film thickness were monitored, and compared with theoretical predictions of thermal growth of waviness. Discrepancies were attributed to imperfect response of the gimbals to axial run-out. This run-out was increased by thermal effects at high sliding speeds and led to interactions which influenced the growth of two-lobed waves on the contact face. Operation proved stable, as predicted, under the carefully controlled operating conditions of fixed axial load and self aligning contact.

An Instability for Parallel Sliding of Solid Surfaces Separated by a Viscous Liquid Film

Thermoelastic phenomena in lubricated face type seals are analyzed for possible instabilities which may lead to large surface deformations and seal failure. Thresholds of such instabilities are found where a small, steadily moving, surface disturbance will neither grow nor decay. For a good thermal conductor sliding on a good insulator, several such thresholds exist. Only one, however, falls within a reasonable operating range, the critical sliding speed being Ucrit=hκ¯KMμαM where h¯ is the nominal film-thickness, κ the wave number of the disturbance, KM the thermal conductivity of the conductor and αM its coefficient of thermal expansion, and μ the viscosity of the oil. Expressions are given for the approximate limits of h¯ within which such a threshold lies. Finally, it is shown that, as expected, a disturbance will grow when U > Ucrit and decay when U < Ucrit.

Clearance, Leakage, and Contact Temperature in a Thermoelastically Deformed Seal-Like Configuration

Equations are derived for clearance, leakage, and contact temperatures for conditions where initially flat rubbing surfaces are deformed thermally to produce a sequence of equally spaced contact patches, separated by regions where the surfaces withdraw from one another. One paradoxical result is that increased contact pressure or preload on the seal increases leakage when sliding takes place above a critical speed.

The Role of Wear in the Initiation of Thermoelastic Instabilities of Rubbing Contact

Thermoelastic instability of rubbing contact results from the interaction of thermal expansion, frictional heating, and conduction of heat away from the contact zone. These interactions are modified by wear, which is shown to damp the growth of disturbances in contact pressure from a nominal uniform value. In some cases the presence of wear is found to give rise to oscillatory behavior where portions of the rubbing surfaces alternately rise and drop in temperature. These effects are analyzed for the case of a two-dimensional scraper or blade moving normal to its edge, which presses against the surface of a stationary semi-infinite body. The roles of material properties and operating variables are delineated in terms of dimensionless parameters appropriate to the system.

Thermal Effects in Contact Fatigue Under Oscillatory Normal Load

Experiments are reported wherein contact fatigue was brought about by the application of an oscillatory normal load between a ball and a flat specimen. Plots of the flat-specimen temperature versus time showed that a rapid temperature rise occurred in the initial stage of crack formation, and thus provided an early indication of fatigue. Thermal resistances were measured for the apparatus components as well as the specimen contact. Using these, it was possible to apply the measured flat-specimen temperature to obtain estimates of the contact temperature as well as the energy dissipation rate prior to the incidence of fatigue cracks. It was shown that the contact temperature did not rise sufficiently to produce annealing in the test specimens. Thus, toroidal rings of hardened and softened material in the stressed zone could not be attributed to thermal transformation of the bearing steel. It was also shown that energy dissipation due to cyclic loading varied in approximate exponential relationship with dynamic load, and decreased upon increase of static load when dynamic load was maintained constant.

Effects of Two-Dimensional, Sinusoidal Roughness on the Load Support Characteristics of a Lubricant Film

An analytical study is made of the effects of two-dimensional, sinusoidal roughness on pressure and shear stress in a lubricant film between two parallel plates engaged in steady, parallel, relative motion. The effects of pressure and heating upon viscosity, as well as shear elasticity are accounted for in the case where roughness height is small relative to film thickness. Second-order influences which contribute to net load support by the film are computed in terms of the first-order solution. The results give evidence as to when boundary roughness may be negligible in its influence on hydrodynamic film calculations. Most important, however, they give evidence of a type of instability which may contribute to film breakdown in some marginal lubrication situations.