Characterization of a voltage-gated K+ channel beta subunit expressed in human heart.

Voltage-gated K+ channels are important modulators of the cardiac action potential. However, the correlation of endogenous myocyte currents with K+ channels cloned from human heart is complicated by the possibility that heterotetrameric alpha-subunit combinations and function-altering beta subunits exist in native tissue. Therefore, a variety of subunit interactions may generate cardiac K+ channel diversity. We report here the cloning of a voltage-gated K+ channel beta subunit, hKv beta 3, from adult human left ventricle that shows 84% and 74% amino acid sequence identity with the previously cloned rat Kv beta 1 and Kv beta 2 subunits, respectively. Together these three Kv beta subunits share > 82% identity in the carboxyl-terminal 329 aa and show low identity in the amino-terminal 79 aa. RNA analysis indicated that hKv beta 3 message is 2-fold more abundant in human ventricle than in atrium and is expressed in both healthy and diseased human hearts. Coinjection of hKv beta 3 with a human cardiac delayed rectifier, hKv1.5, in Xenopus oocytes increased inactivation, induced an 18-mV hyperpolarizing shift in the activation curve, and slowed deactivation (tau = 8.0 msec vs. 35.4 msec at -50 mV). hKv beta 3 was localized to human chromosome 3 by using a human/rodent cell hybrid mapping panel. These data confirm the presence of functionally important K+ channel beta subunits in human heart and indicate that beta-subunit composition must be accounted for when comparing cloned channels with endogenous cardiac currents.

The weediness of wild plants: molecular analysis of genes influencing dispersal and persistence of johnsongrass, Sorghum halepense (L.) Pers.

Many major weeds rely upon vegetative dispersal by rhizomes and seed dispersal by "shattering" of the mature inflorescence. We report molecular analysis of these traits in a cross between cultivated and wild species of Sorghum that are the probable progenitors of the major weed "johnsongrass." By restriction fragment length polymorphism mapping, variation in the number of rhizomes producing above-ground shoots was associated with three quantitative trait loci (QTLs). Variation in regrowth (ratooning) after overwintering was associated with QTLs accounting for additional rhizomatous growth and with QTLs influencing tillering. Vegetative buds that become rhizomes are similar to those that become tillers--one QTL appears to influence the number of such vegetative buds available, and additional independent genes determine whether individual buds differentiate into tillers or rhizomes. DNA markers described herein facilitate cloning of genes associated with weediness, comparative study of rhizomatousness in other Poaceae, and assessment of gene flow between cultivated and weedy sorghums--a risk that constrains improvement of sorghum through biotechnology. Cloning of "weediness" genes may create opportunities for plant growth regulation, in suppressing propagation of weeds and enhancing productivity of major forage, turf, and "ratoon" crops.

Fusion of the TEL gene on 12p13 to the AML1 gene on 21q22 in acute lymphoblastic leukemia.

Chromosomal rearrangements involving band 12p13 are found in a wide variety of human leukemias but are particularly common in childhood acute lymphoblastic leukemia. The genes involved in these rearrangements, however, have not been identified. We now report the cloning of a t(12;21) translocation breakpoint involving 12p13 and 21q22 in two cases of childhood pre-B acute lymphoblastic leukemia, in which t(12;21) rearrangements were not initially apparent. The consequence of the translocation is fusion of the helix-loop-helix domain of TEL, an ETS-like putative transcription factor, to the DNA-binding and transactivation domains of the transcription factor AML1. These data show that TEL, previously shown to be fused to the platelet-derived growth factor receptor beta in chronic myelomonocytic leukemia, can be implicated in the pathogenesis of leukemia through its fusion to either a receptor tyrosine kinase or a transcription factor. The TEL-AML1 fusion also indicates that translocations affecting the AML1 gene can be associated with lymphoid, as well as myeloid, malignancy.

LEM1, an ATP-binding-cassette transporter, selectively modulates the biological potency of steroid hormones.

The rat glucocorticoid receptor confers hormone-dependent transcriptional enhancement when expressed in yeast, thereby enabling the genetic identification of nonreceptor proteins that function in the hormone signal-transduction pathway. We isolated a yeast mutant, lem1, with increased sensitivity to dexamethasone and triamcinolone acetonide; responsiveness to a third agonist, deoxycorticosterone, is unaffected. Cloning of wild-type LEM1 revealed a putative transport protein of the ATP-binding cassette family. Dexamethasone accumulation is increased in lem1 cells, suggesting that wild-type LEM1 decreases dexamethasone potency by exporting this ligand. LEM1 appears to affect certain steroids and not others. We propose that transporters like LEM1 can selectively modulate the intracellular levels of steroid hormones. Differential activities of such transporters in mammalian cells might regulate hormone availability and thereby hormone signaling in a cell-type specific manner.

A serine proteinase inhibitor locus at 18q21.3 contains a tandem duplication of the human squamous cell carcinoma antigen gene.

The squamous cell carcinoma antigen (SCCA) is a member of the ovalbumin family of serine proteinase inhibitors (serpins). A neutral form of the protein is found in normal and some malignant squamous cells, whereas an acidic form is detected exclusively in tumor cells and in the circulation of patients with squamous cell tumors. In this report, we describe the cloning of the SCCA gene from normal genomic DNA. Surprisingly, two genes were found. They were tandemly arrayed and flanked by two other closely related serpins, plasminogen activator inhibitor type 2 (PAI2) and maspin at 18q21.3. The genomic structure of the two genes, SCCA1 and SCCA2, was highly conserved. The predicted amino acid sequences were 92% identical and suggested that the neutral form of the protein was encoded by SCCA1 and the acidic form was encoded by SCCA2. Further characterization of the region should determine whether the differential expression of the SCCA genes plays a causal role in development of more aggressive squamous cell carcinomas.

Reconstitution of p53-ubiquitinylation reactions from purified components: the role of human ubiquitin-conjugating enzyme UBC4 and E6-associated protein (E6AP).

The E6 protein of the high-risk human papillomaviruses inactivates the tumor suppressor protein p53 by stimulating its ubiquitinylation and subsequent degradation. Ubiquitinylation is a multistep process involving a ubiquitin-activating enzyme, one of many distinct ubiquitin-conjugating enzymes, and in certain cases, a ubiquitin ligase. In human papillomavirus-infected cells, E6 and the E6-associated protein are thought to act as a ubiquitin-protein ligase in the ubiquitinylation of p53. Here we describe the cloning of a human ubiquitin-conjugating enzyme that specifically ubiquitinylates E6-associated protein. Furthermore, we define the biochemical pathway of p53 ubiquitinylation and demonstrate that in vivo inhibition of various components in the pathway leads to an inhibition of E6-stimulated p53 degradation.

Influence of nitrogen deficiency on senescence and the amounts of RNA and proteins in wheat leaves

Senescence-associated coordination in amounts of enzymes localized in different cellular compartments were determined in attached leaves of young wheat (Triticum aestivum L. cv. Arina) plants. Senescence was initiated at the time of full leaf elongation based on declines in total RNA and soluble protein. Removal of N from the growth medium just at the time of full leaf elongation enhanced the rate of senescence. Sustained declines in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39), and a marked decrease in the rbcS transcripts, just after full leaf elongation indicated that Rubisco synthesis/degradation was very sensitive to the onset of senescence. Rubisco activase amount also declined during senescence but the proportion of rca transcript relative to the total poly A RNA pool increased 3-fold during senescence. Thus, continued synthesis of activase may be required to maintain functional Rubisco throughout senescence. N stress led to declines in the amount of proteins located in the chloroplast, the peroxisome and the cytosol. Transcripts of the Clp protease subunits also declined in response to N stress, indicating that Clp is not a senescence-specific protease. In contrast to the other proteins, mitochondrial NADH-glutamate dehydrogenase (EC 1.4.1.2) was relatively stable during senescence and was not affected by N stress. During natural senescence with adequate plant nitrate supply the amount of nitrite reductase (EC 1.7.7.1) increased, and those of glutamine synthetase (EC 1.4.7.1) and glutamate synthase (EC 6.3.1.2) were stable. These results indicated that N assimilatory capacity can continue or even increase during senescence if the substrate supply is maintained. Differential stabilities of proteins, even within the same cellular compartment, indicate that proteolytic activity during senescence must be highly regulated.

International Union of Pharmacology. LXIX. Status of the calcitonin gene-related peptide subtype 2 receptor

Historically, calcitonin gene-related peptide (CGRP) receptors have been divided into two classes, CGRP(1) and CGRP(2).After the cloning of calcitonin receptor-like receptor (CLR) and receptor activity-modifying proteins (RAMPs), it became clear that the CGRP(1) receptor was a complex between CLR and RAMP1. It is now apparent that the CGRP(2) receptor phenotype is the result of CGRP acting at receptors for amylin and adrenomedullin. Accordingly, the term "CGRP(2)" receptor should no longer be used, and the "CGRP(1)" receptor should be known as the "CGRP" receptor.

A new randomization assay reveals Unexpected elements of sequence bias in model 'randomized' gene libraries:Implications for biopanning

Although techniques such as biopanning rely heavily upon the screening of randomized gene libraries, there is surprisingly little information available on the construction of those libraries. In general, it is based on the cloning of 'randomized' synthetic oligonucleotides, in which given position(s) contain an equal mixture of all four bases. Yet, many supposedly 'randomized' libraries contain significant elements of bias and/or omission. Here, we report the development and validation of a new, PCR-based assay that enables rapid examination of library composition both prior to and after cloning. By using our assay to analyse model libraries, we demonstrate that the cloning of a given distribution of sequences does not necessarily result in a similarly composed library of clones. Thus, while bias in randomized synthetic oligonucleotide mixtures can be virtually eliminated by using unequal ratios of the four phosphoramidites, the use of such mixtures does not ensure retrieval of a truly randomized library. We propose that in the absence of a technique to control cloning frequencies, the ability to analyse the composition of libraries after cloning will enhance significantly the quality of information derived from those libraries. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Genetic and Molecular Basis of Encapsulation and Capsule Diversity in Kingella kingae

Kingella kingae is a bacterial pathogen that is increasingly recognized as an etiology of septic arthritis, osteomyelitis, bacteremia, and endocarditis in young children. The pathogenesis of K. kingae disease starts with bacterial adherence to the respiratory epithelium of the posterior pharynx. Previous work has identified type IV pili and a trimeric autotransporter protein called Knh (Kingella NhhA homolog) as critical factors for adherence to human epithelial cells. Additional studies established that the presence of a polysaccharide capsule interferes with Knh-mediated adherence. Given the inhibitory role of capsule during adherence we sought to uncover the genes involved in capsule expression to understand how capsule is elaborated on the cell surface. Additionally, this work aimed to further characterize capsule diversity among K. kingae clinical isolates and to investigate the relationship between capsule type and site of isolation.

We first set out to identify the carbohydrates present in the K. kingae capsule present in the prototype strain 269-492. Glycosyl composition and NMR analysis of surface extractable polysaccharides demonstrated two distinct polysaccharides, one consisting of GalNAc and Kdo with the structure →3)-β-GalpNAc-(1→5)-β-Kdop-(2→ and the other containing galactose alone with the structure →5)-β-Galf-(1→.

To discern the two polysaccharides we disrupted the ctrA gene required for surface localization of the K. kingae polysaccharide capsule and observed a loss of GalNAc and Kdo but no effect on the presence of Gal in bacterial surface extracts. In contrast, deletion of the pamABCDE locus involved in production of a reported galactan exopolysaccharide eliminated Gal but had no effect on the presence of GalNAc and Kdo in surface extracts. These results established that K. kingae strain KK01 produces a polysaccharide capsule with the structure →3)-β-GalpNAc-(1→5)-β-Kdop-(2→ and a separate exopolysaccharide with the structure →5)-β-Galf-(1→.

Having established that K. kingae produces a capsule comprised of GalNAc and Kdo, we next set out to identify the genetic determinants of capsule through a transposon mutagenesis screen. In addition to the previously identified ctrABCD operon, lipA, lipB, and a putative glycosyltransferase termed csaA (capsule synthesis region A gene A) were found to be essential for the production of surface-localized capsule. The ctr operon, lipA, lipB, and csaA were found to be present at unlinked locations throughout the genome, which is atypical for gram-negative organisms that elaborate a capsule dependent on an ABC-type transporter for surface localization. Through examining capsule localization in the ctrA, lipA, lipB, and csaA mutant strains, we determined that the ctrABCD, lipA/lipB, and csaA gene products respectively function in capsule export, assembly, and synthesis, respectively. The GalNAc transferase and Kdo transferase domains found in CsaA further support its role in catalyzing the synthesis of the GalNAc-Kdo capsule in the K. kingae prototype strain.

To investigate the capsule diversity that exists in K. kingae we screened a panel of strains isolated from patients with invasive disease or healthy carriers for the csaA capsule synthesis locus. We discovered that Kingella kingae expresses one of 4 capsule synthesis loci (csa, csb, csc, or csd) associated with a capsule consisting of Kdo and GalNAc (type a), Kdo and GlcNAc (type b), Kdo and ribose (type c), and GlcNAc and galactose (type d), respectively. Cloning of the csa, csb, csc, or csd locus into the empty flanking gene region in a non-encapsulated mutant (creation of an isogenic capsule swap) was sufficient to produce either the type a, type b, or type c capsule, respectively, further supporting the role of these loci in expression of a specific polysaccharide linkage. Capsule type a and capsule type b accounted for 96% of invasive strains. Conversely, capsule type c and capsule type d were found disproportionately among carrier isolates, suggesting that capsule type is important in promoting invasion and dissemination.

In conclusion, we discovered that Kingella kingae expresses a polysaccharide capsule and an exopolysaccharide on its surface that require distinct genetic loci for surface localization. Further investigation into genetic determinants of encapsulation revealed the loci ctrABCD, lipA/lipB, and a putative glycosyltransferase are required for capsule expression, with the gene products having roles in capsule export, assembly, and synthesis, respectively. The putative glycosyltransferase CsaA was determined to be a bifunctional enzyme with both GalNAc-transferase and Kdo-transferase activity. Furthermore, we discovered a total of 4 capsule types expressed in clinical isolates of K. kingae, each with a distinct capsule synthesis locus. The variation in the proportion of capsule types found between invasive strains and carriage strains suggest that capsule type is important in promoting invasion and dissemination. Taken together, this work expands our knowledge of the capsule types expressed among K. kingae carrier and invasive isolates and provides insights into the common genetic determinants of capsule expression. These contributions may lead to selecting clinically relevant capsule types to develop into a capsule based vaccine to prevent K. kingae colonization.

Seawater carbonate chemistry and the photophysiology of Thalassiosira pseudonana (Bacillariophyceae) and Emiliania huxleyi (Haptophyta) in a laboratory experiment

Increasing anthropogenic carbon dioxide is causing changes to ocean chemistry, which will continue in a predictable manner. Dissolution of additional atmospheric carbon dioxide leads to increased concentrations of dissolved carbon dioxide and bicarbonate and decreased pH in ocean water. The concomitant effects on phytoplankton ecophysiology, leading potentially to changes in community structure, are now a focus of concern. Therefore, we grew the coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler and the diatom strains Thalassiosira pseudonana (Hust.) Hasle et Heimdal CCMP 1014 and T. pseudonana CCMP 1335 under low light in turbidostat photobioreactors bubbled with air containing 390 ppmv or 750 ppmv CO2. Increased pCO2 led to increased growth rates in all three strains. In addition, protein levels of RUBISCO increased in the coastal strains of both species, showing a larger capacity for CO2 assimilation at 750 ppmv CO2. With increased pCO2, both T. pseudonana strains displayed an increased susceptibility to PSII photoinactivation and, to compensate, an augmented capacity for PSII repair. Consequently, the cost of maintaining PSII function for the diatoms increased at increased pCO2. In E. huxleyi, PSII photoinactivation and the counter-acting repair, while both intrinsically larger than in T. pseudonana, did not change between the current and high-pCO2 treatments. The content of the photosynthetic electron transport intermediary cytochrome b6/f complex increased significantly in the diatoms under elevated pCO2, suggesting changes in electron transport function.

Purification, biochemical characterization and localization at single cell resolution of Matrix Gla Protein (MGP) and Bone Gla Protein (BGP) in the teleost fish Argyrosomus regius

Tese de dout. em Química, Faculdade de Ciências do Mar e do Ambiente, Univ. do Algarve, 2002

Functional characterization by genetic complementation of aroB-Encoded dehydroquinate synthase from Mycobactetium tuberculosis H37Rv and its heterologous expression and purification

The recent recrudescence of Mycobacterium tuberculosis infection and the emergence of multidrug-resistant strains have created an urgent need for new therapeutics against tuberculosis. The enzymes of the shikimate pathway are attractive drug targets because this route is absent in mammals and, in M. tuberculosis, it is essential for pathogen viability. This pathway leads to the biosynthesis of aromatic compounds, including aromatic amino acids, and it is found in plants, fungi, bacteria, and apicomplexan parasites. The aroB-encoded enzyme dehydroquinate synthase is the second enzyme of this pathway, and it catalyzes the cyclization of 3-deoxy-D-arabino-heptulosonate-7-phosphate in 3-dehydroquinate. Here we describe the PCR amplification and cloning of the aroB gene and the overexpression and purification of its product, dehydroquinate synthase, to homogeneity. In order to probe where the recombinant dehydroquinate synthase was active, genetic complementation studies were performed. The Escherichia coli AB2847 mutant was used to demonstrate that the plasmid construction was able to repair the mutants, allowing them to grow in minimal medium devoid of aromatic compound supplementation. In addition, homogeneous recombinant M. tuberculosis dehydroquinate synthase was active in the absence of other enzymes, showing that it is homomeric. These results will support the structural studies with M. tuberculosis dehydroquinate synthase that are essential for the rational design of antimycobacterial agents.

A myosin from a higher plant has structural similarities to class V myosins

In plant cells, myosin is believed to be the molecular motor responsible for actin-based motility processes such as cytoplasmic streaming and directed vesicle transport. In an effort to characterize plant myosin, a cDNA encoding a myosin heavy chain was isolated from Arabidopsis thaliana. The predicted product of the MYA1 gene is 173 kDa and is structurally similar to the class V myosins. It is composed of the highly-conserved NH2-terminal "head" domain, a putative calmodulin-binding "neck" domain an alpha-helical coiled-coil domain, and a COOH-terminal domain. Northern blot analysis shows that the Arabidopsis MYA1 gene is expressed in all the major plant tissues (flower, leaf, root, and stem). We suggest that the MYA1 myosin may be involved in a general intracellular transport process in plant cells.

An asparaginyl endopeptidase mediates in vivo protein backbone cyclization

Proteases can catalyze both peptide bond cleavage and formation, yet the hydrolysis reaction dominates in nature. This presents an interesting challenge for the biosynthesis of backbone cyclized (circular) proteins, which are encoded as part of precursor proteins and require post-translational peptide bond formation to reach their mature form. The largest family of circular proteins are the plant-produced cyclotides; extremely stable proteins with applications as bioengineering scaffolds. Little is known about the mechanism by which they are cyclized in vivo but a highly conserved Asn (occasionally Asp) residue at the C terminus of the cyclotide domain suggests that an enzyme with specificity for Asn (asparaginyl endopeptidase; AEP) is involved in the process. Nicotiana benthamiana does not endogenously produce circular proteins but when cDNA encoding the precursor of the cyclotide kalata B1 was transiently expressed in the plants they produced the cyclotide, together with linear forms not commonly observed in cyclotide-containing plants. Observation of these species over time showed that in vivo asparaginyl bond hydrolysis is necessary for cyclization. When AEP activity was suppressed, either by decreasing AEP gene expression or using a specific inhibitor, the amount of cyclic cyclotide in the plants was reduced compared with controls and was accompanied by the accumulation of extended linear species. These results suggest that an AEP is responsible for catalyzing both peptide bond cleavage and ligation of cyclotides in a single processing event.