Isolation of a novel plant lectin with an unusual specificity from Calystegia sepium

A novel plant lectin has been isolated from the rhizomes of Calystegia sepium (hedge bindweed) and partially characterized. The lectin is a dimeric protein composed of two identical non-covalently linked subunits of 16 kDa. Hapten inhibition studies indicate that the novel lectin is best inhibited by maltose and mannose and hence exhibits a sugar binding specificity that differs in some respects from that of all previously isolated plant lectins. Mitogenicity tests have shown that the Calystegia lectin is a powerful T-cell mitogen. Affinity purification of human, plant and fungal glycoproteins on immobilized C. sepium lectin demonstrates that this novel lectin can be used for the isolation of glycoconjugates from various sources. Moreover, it can be expected that by virtue of its distinct specificity, the new lectin will become an important tool in glycobiology.

Isolation, characterization and molecular cloning of the mannose-binding lectins from leaves and roots of garlic (Allium sativum L.)

Two novel lectins were isolated from roots and leaves of garlic. Characterization of the purified proteins indicated that the leaf lectin ASAL is a dimer of two identical subunits of 12 kDa, which closely resembles the leaf lectins from onion, leek and shallot with respect to its molecular structure and agglutination activity. In contrast, the root lectin ASARI, which is a dimer of subunits of 15 kDa, strongly differs from the leaf lectin with respect to its agglutination activity. cDNA cloning of the leaf and root lectins revealed that the deduced amino acid sequences of ASAL and ASARI are virtually identical. Since both lectins have identical N-terminal sequences the larger Mr of the ASARI subunits implies that the root lectin has an extra sequence at its C-terminus. These results not only demonstrate that virtually identical precursor polypeptides are differently processed at their C-terminus in roots and leaves but also indicate that differential processing yields mature lectins with strongly different biological activities. Further screening of the cDNA library for garlic roots also yielded a cDNA clone encoding a protein composed of two tandemly arrayed lectin domains. Since the presumed two-domain root lectin has not been isolated yet, its possible relationship to the previously described two-domain bulb lectin could not be studied at the protein level.

Lectin and alliinase are the predominant proteins in nectar from leek (Allium porrum L.) flowers

Analysis of nectar from leek (Allium porrum) flowers by SDS-PAGE revealed the presence of two major polypeptide bands of 50 kDa and 13 kDa, respectively. Using a combination of agglutination tests, enzyme assays and N-terminal sequencing, the polypeptides have been identified as subunits of alliin lyase (alliinase, EC 4.4.1.4) and mannose-binding lectin, respectively. The latter protein is particularly abundant since it represents about 75% of the total nectar protein. Honey produced by bees foraging on flowering leek plants still contains biologically active lectin and alliinase. However, the levels of both proteins are strongly reduced as compared to those in the original nectar. It is evident, therefore, that the lectin as well as the alliinase are inactivated/degraded during the conversion of nectar into honey.

Molecular cloning and further characterization of rat peroxisomal trihydroxycoprostanoyl-CoA oxidase

The composite trihydroxycoprostanoyl-CoA oxidase cDNA sequence, derived from overlapping clones isolated via screening of two different rat liver expression libraries, consisted of 2509 bases and contained an open reading frame of 2046 bases, encoding a protein of 681 amino acids with a calculated molecular mass of 76711 Da. The reading frame and identity of the trihydroxycoprostanoyl-CoA oxidase cDNA were confirmed by the location of various tryptic peptides, obtained from the purified enzyme, in the deduced amino acid sequence. The C-terminus (His-Lys-Met) of trihydroxycoprostanoyl-CoA oxidase did not seem to interact with the C-terminal peroxisomal targeting signal 1 (PTS1) import receptor, although the tripeptide fits the rule of conserved PTS1 variants for targeting of proteins to glycosomes of Trypanosomatidae. At the protein level, trihydroxycoprostanoyl-CoA oxidase showed 45% identical amino acids with rat palmitoyl-CoA oxidase, whereas the identity with pristanoyl-CoA oxidase was much lower (22%). Northern analysis of multiple rat tissues revealed a signal (approx. 2.6 kb) only in liver and (although much weaker) in kidney. Dot-blot analysis of total liver RNA revealed that the mRNA for trihydroxy-coprostanoyl-CoA oxidase is not induced after treatment of rats with structurally unrelated peroxisome proliferators and indicates that highly similar mRNAs are present in other mammals, including man. Immunocytochemistry showed a decrease in trihydroxycoprostanoyl-CoA oxidase protein in individual liver peroxisomes ('diluting-out effect') after treatment of rats with bezafibrate, whereas the palmitoyl-CoA oxidase labelling was significantly increased.

Amyloidogenic processing of human amyloid precursor protein in hippocampal neurons devoid of cathepsin D

betaA4-Amyloid peptide, the main component of the amyloid plaques in the brain of Alzheimer's disease patients is produced from amyloid precursor protein (APP) by proteolytical processing. Several lines of evidence suggest a direct role for cathepsin D, the major endosomal/lysosomal aspartic endopeptidase, in betaA4-amyloid peptide generation. Here we tested this hypothesis using primary cultures of hippocampal neurons derived from cathepsin D-deficient (knock out) mice and expressing wild-type human APP and two clinical APP variants via recombinant Semliki Forest virus. We demonstrate APP secretory processing, production of carboxyl-terminal amyloid fragments, and secretion of the betaA4-amyloid peptide in the complete absence of cathepsin D. The results rule out cathepsin D as a critical component of alpha-, beta-, or gamma-secretase and therefore as a primary target for drugs aimed at decreasing the betaA4-amyloid peptide burden in Alzheimer's disease.

Murine alpha-macroglobulins demonstrate divergent activities as neutralizers of transforming growth factor-beta and as inducers of nitric oxide synthesis. A possible mechanism for the endotoxin insensitivity of the alpha2-macroglobulin gene knock-out mouse

alpha2-Macroglobulin null mice demonstrate increased resistance to endotoxin challenge (Umans, L., Serneels, L., Overbergh, L., Van Leuven, F., and Van den Berghe, H. (1995) J. Biol. Chem. 270, 19778-19785). We hypothesized that this phenotype might reflect the function of murine alpha2M (malpha2M) as a neutralizer of transforming growth factor-beta (TGF-beta) and inducer of nitric oxide synthesis in vivo. When incubated with wild-type mouse plasma, TGF-beta1 and TGF-beta2 bound only to malpha2M. Alternative TGF-beta-binding proteins were not detected in plasma from alpha2M(-/-) mice. Wild-type mouse plasma, but not plasma from alpha2M(-/-) mice, inhibited TGF-beta1 binding to TGF-beta receptors on fibroblasts. Purified malpha2M bound TGF-beta1 and TGF-beta2 with similar affinity; the KD values were 28 +/- 4 and 33 +/- 4 nM, respectively. Murinoglobulin, the second murine alpha-macroglobulin, bound both TGF-beta isoforms with 30-fold lower affinity. Malpha2M counteracted the activities of TGF-beta1 and TGF-beta2 in an endothelial cell growth assay. Malpha2M also induced NO synthesis when incubated with RAW 264.7 cells, an activity which probably results from the neutralization of autocrine TGF-beta activity. Human alpha2M induced NO synthesis comparably to malpha2M; however, MUG had no effect. These studies demonstrate that the ability to neutralize TGF-beta is a property of malpha2M, which is not redundant in the murine alpha-macroglobulin family or in murine plasma. Malpha2M is the only murine alpha-macroglobulin that promotes NO synthesis. The absence of malpha2M, in alpha2M(-/-) mice, may allow TGF-beta to more efficiently suppress excessive iNOS expression following endotoxin challenge.

The beta-amyloid domain is essential for axonal sorting of amyloid precursor protein

We have analysed the axonal sorting signals of amyloid precursor protein (APP). Wild-type and mutant versions of human APP were expressed in hippocampal neurons using the Semliki forest virus system. We show that wild-type APP and mutations implicated in Alzheimer's disease and another brain beta-amyloidosis are sorted to the axon. By analysis of deletion mutants we found that the membrane-inserted APP ectodomain but not the cytoplasmic tail is required for axonal sorting. Systematic deletions of the APP ectodomain identified two regions required for axonal delivery: one encoded by exons 11-15 in the carbohydrate domain, the other encoded by exons 16-17 in the juxtamembraneous beta-amyloid domain. Treatment of the cells with the N-glycosylation inhibitor tunicamycin induced missorting of wild-type APP, supporting the importance of glycosylation in axonal sorting of APP. The data revealed a hierarchy of sorting signals on APP: the beta-amyloid-dependent membrane proximal signal was the major contributor to axonal sorting, while N-glycosylation had a weaker effect. Furthermore, recessive somatodendritic signals, most likely in the cytoplasmic tail, directed the protein to the dendrites when the ectodomain was deleted. Analysis of detergent solubility of APP and another axonally delivered protein, hemagglutinin, demonstrated that only hemagglutinin formed CHAPS-insoluble complexes, suggesting distinct mechanisms of axonal sorting for these two proteins. This study is the first delineation of sorting requirements of an axonally targeted protein in polarized neurons and indicates that the beta-amyloid domain plays a major role in axonal delivery of APP.

Antimicrobial peptides from Mirabilis jalapa and Amaranthus caudatus: expression, processing, localization and biological activity in transgenic tobacco

The cDNAs encoding the seed antimicrobial peptides (AMPs) from Mirabilis jalapa (Mj-AMP2) and Amaranthus caudatus (Ac-AMP2) have previously been characterized and it was found that Mj-AMP2 and Ac-AMP2 are processed from a precursor preprotein and preproprotein, respectively [De Bolle et al., Plant Mol Biol 28:713-721 (1995) and 22:1187-1190 (1993), respectively]. In order to study the processing, sorting and biological activity of these antimicrobial peptides in transgenic tobacco, four different gene constructs were made: a Mj-AMP2 wild-type gene construct, a Mj-AMP2 mutant gene construct which was extended by a sequence encoding the barley lectin carboxyl-terminal propeptide, a known vacuolar targeting signal [Bednarek and Raikhel, Plant Cell 3: 1195-1206 (1991)]; an Ac-AMP2 wild-type gene construct; and finally, an Ac-AMP2 mutant gene construct which was truncated in order to delete the sequence encoding the genuine carboxyl-terminal propeptide. Processing and localization analysis indicated that an isoform of Ac-AMP2 with a cleaved-off carboxyl-terminal arginine was localized in the intercellular fluid fraction of plants expressing either wild-type or mutant gene constructs. Mj-AMP2 was recovered extracellularly in plants transformed with Mj-AMP2 wild-type gene construct, whereas an Mj-AMP2 isoform with a cleaved-off carboxyl-terminal arginine accumulated intracellularly in plants expressing the mutant precursor protein with the barley lectin propeptide. The in vitro antifungal activity of the AMPs purified from transgenic tobacco expressing any of the four different precursor proteins was similar to that of the authentic proteins. However, none of the transgenic plants showed enhanced resistance against infection with either Botrytis cinerea or Alternaria longipes.

Rat pristanoyl-CoA oxidase. cDNA cloning and recognition of its C-terminal (SQL) by the peroxisomal-targeting signal 1 receptor

The composite pristanoyl-CoA oxidase cDNA sequence, derived from two overlapping clones from a rat liver cDNA library and a 5'-RACE (rapid amplification of cDNA ends) PCR fragment, consisted of 2600 bases and contained an open reading frame of 2100 bases, encoding a protein of 700 amino acids with a calculated molecular mass of 78445 Da. This value is somewhat larger than the reported molecular mass of 70 kDa as determined earlier by SDS-gel electrophoresis. The amino acid identity with rat palmitoyl-CoA oxidase was rather low (28%) and barely higher than that with the yeast acyl-CoA oxidases (20%), suggesting that the palmitoyl-CoA oxidase/pristanoyl-CoA oxidase duplication occurred early in evolution. The carboxy-terminal tripeptide of pristanoyl-CoA oxidase was SQL. In vitro studies with the bacterially expressed human peroxisomal-targeting signal-1 import receptor indicated that SQL functions as a peroxisome-targeting signal. Northern analysis of tissues from control and clofibrate treated rats demonstrated that the pristanoyl-CoA oxidase gene is transcribed in liver and extrahepatic tissues and that transcription is not enhanced by treatment of rats with peroxisome proliferators. No mRNA could be detected by northern analysis of human tissues, suggesting that the human pristanoyl-CoA oxidase gene, if present, is only poorly or not transcribed.

Molecular cloning of the lectin and a lectin-related protein from common Solomon's seal (Polygonatum multiflorum)

The most prominent protein of Polygonatum multiflorum (common Solomon's seal) rhizomes has been identified as a mannose-binding lectin. Analysis of the purified lectin demonstrated that it is a tetramer of four identical subunits of 14 kDa. Molecular cloning further revealed that the lectin from this typical Liliaceae species belongs to the superfamily of monocot mannose-binding proteins. Screening of cDNA libraries constructed with RNA isolated from buds, leaves and flowers of P. multiflorum also yielded cDNA clones encoding a protein, which contains two tandemly arranged domains with an obvious sequence homology to the mannose-binding lectins. Molecular modelling of the Polygonatum lectin and lectin-related protein indicated that the three-dimensional structure of both proteins strongly resembles that of the snowdrop lectin. In addition, this approach suggested that the presumed carbohydrate-binding sites of the lectin can accommodate a mannose residue whereas most of the carbohydrate-binding sites of the lectin-related protein cannot.

Characterization and molecular cloning of Sambucus nigra agglutinin V (nigrin b), a GalNAc-specific type-2 ribosome-inactivating protein from the bark of elderberry (Sambucus nigra)

The molecular structure of the Sambucus nigra agglutinin V (SNAV), which has been described previously as a type-2 ribosome-inactivating protein called nigrin b, has been studied in detail by analysis of the purified protein combined with cDNA cloning and molecular modelling. Native SNAV is a dimer of two [A-s-s-B] pairs. Hapten inhibition assays indicated that GalNAc is a 20-fold more potent inhibitor of SNAV than Gal. A cDNA clone encoding SNAV was isolated from a cDNA library constructed with mRNA from the bark. Sequence analysis of this cDNA revealed a striking similarity to the recently cloned NeuAc alpha-2,6-gal/GalNAc-specific S. nigra bark agglutinin I (SNAI) and to the previously sequenced type-2 ribosome-inactivating proteins from Ricinus communis and Abrus precatorius. In addition, molecular modelling of SNAV further suggested that its structure closely resembles that of ricin. The N-terminal sequence of the B chain of SNAV also shows a marked similarity with the polypeptide of the previously described GalNAc-specific s. nigra bark agglutinin II (SNAII), which unlike SNAV and SNAI has no ribosome-inactivating activity. It appears, therefore, that elderberry bark contains at least two different type-2 ribosome-inactivating proteins and a lectin built up of subunits which are closely related to the B chain of SNAV.

Acute Chagas' disease: plasma levels of alpha-2-macroglobulin and C-reactive protein in children under 13 years in a high endemic area of Bolivia

We measured the levels of two human acute phase proteins (APP), alpha-2-macroglobulin (A2M) and C-reactive protein (CRP), in sera of 56 healthy and 84 acute chagasic children aged from 1 to 13 years old, from a highly endemic area in Bolivia. In such areas, children are continuously exposed to vectors and the frequency of acute cases increases with age. Quantitation of A2M and CRP were performed using sandwich ELISAs, that were shown to be sensitive, reproducible and suited for studying many samples rapidly. A2M levels observed were higher in healthy younger children, decreasing with age until children reached their teens, and their distribution suggested a relationship between A2M concentration and age that could be consistently expressed by a power function. The same does not occur with CRP levels. Concentrations of A2M were age-adjusted to allow comparison using sera collected from children with different ages. Both A2M and CRP were significantly increased in acute chagasic children. Since parasites are commonly present in blood and tissues during the acute phase of Chagas' disease, it is possible that the high levels of A2M may act as inhibitors of a high load of proteinases, derived either from the parasites, from host cell damage or from both.

Expression in brain of amyloid precursor protein mutated in the alpha-secretase site causes disturbed behavior, neuronal degeneration and premature death in transgenic mice

A double mutation in the alpha-secretase site in the betaA4 region of mouse amyloid precursor protein (APP) reduced its secretion from COS cells, polarized MDCK cells and rat primary neurons. Expression of this mutant in the brain of mice, using the neuron-specific elements of the mouse Thy-1 gene promoter, resulted in transgenic mice that became progressively hyperactive, displayed seizures and died prematurely. In three different transgenic lines the severity of the phenotype was related directly to the expression levels of the transgene, estimated by both mRNA and protein levels. In addition, homozygous mice derived from each transgenic strain showed more severe symptoms which also occurred earlier in life than in heterozygotes. The observed symptoms were, however, not essentially different in the different lines. Increased aggressiveness, disturbed responses to kainic acid and N-methyl-D-aspartate, neophobia and deficiency in exploratory behavior were demonstrated in these mice. In the brain, the observed neuropathological changes included necrosis, apoptosis and astrogliosis in the hippocampus, cortex and other areas. The data demonstrate that incomplete or incorrect alpha-secretase processing of APP results in severe neurotoxicity and that this effect is expressed in a dominant manner.

Molecular cloning of two different mannose-binding lectins from tulip bulbs

Two lectins were isolated from the bulbs of Tulipa cv. Apeldoorn and their corresponding cDNA clones analyzed. The first, called TxLMII (second mannose-binding Tulipa hybrid lectin), is a novel mannose-binding tulip lectin. Based on its molecular structure, carbohydrate-binding specificity and amino acid sequence, TxLMII belongs to the superfamily of mannose-binding monocot lectins which are also found in representatives of the plant families Amaryllidaceae, Alliaceae, Orchidaceae and Araceae. Molecular cloning of the second lectin, called TxLCI (first Tulipa hybrid lectin with complex specificity), allowed determination unambiguously of the molecular structure of this previously described protein. In addition, evidence is presented that each TxLCI subunit possesses a mannose-binding site and an N-acetylgalactosamine-binding site, which act independently of each other. Both binding sites are located in a separate domain of the lectin polypeptide. Since the first domain of TxLCI shows sequence similarity to TxLMII, it is suggested that their genes evolved from a common ancestor.

Acute-phase proteins and serologic profiles of chagasic children from an endemic area in Bolivia

Chagas' disease represents a major public health problem in Latin America. In endemic areas, it is important to detect acute and even asymptomatic infections in children so that specific therapy can be started immediately. We studied 203 sera from children from the region of Cochabamba, Bolivia. A high percentage of seropositive individuals was found in the three villages studies. Levels of alpha-2 macroglobulin (A2M) and C-reactive protein (CRP) increased in a significant number of children with acute Chagas' disease. The combined analysis of serologic and biochemical parameters can define the different stages of acute infection by Trypanosoma cruzi: 1) an early stage, with an increase only in specific immunoglobulin M (IgM) levels; 2) intermediate stages, with high specific IgM and IgG levels and/or high anti-galactose (anti-Gal) levels and increased A2M and/or CRP levels; and 3) a late acute stage, with low IgM levels but high A2M, CRP, anti-Gal, and specific IgG levels. The detection of high IgG levels alone is indicative of the chronic/indeterminate stage of Chagas' disease. We also show serologic differences between seropositive asymptomatic villagers and symptomatic patients undergoing medical care; asymptomatic cases presented higher levels of A2M and lower levels of specific antibodies.

The NeuAc(alpha-2,6)-Gal/GalNAc-binding lectin from elderberry (Sambucus nigra) bark, a type-2 ribosome-inactivating protein with an unusual specificity and structure

The cDNA encoding the NeuAc(alpha-2,6)Gal/GalNAc binding lectin from elderberry (Sambucus nigra) bark (SNAI) was isolated from a cDNA library constructed with mRNA from the bark. Sequence analysis of this lectin cDNA revealed a striking similarity to the previously sequenced type-2 ribosome-inactivating proteins from Ricinus communis and Abrus precatorius. Molecular modelling of SNAI further indicated that its structure closely resembles that of ricin. Since SNAI strongly inhibits cell-free protein synthesis in a rabbit reticulocyte lysate it presumably is a type-2 ribosome-inactivating protein. However, SNAI differs from all previously described type-2 ribosome-inactivating proteins by its specificity towards NeuAc(alpha-2,6)Gal/GalNAc and its unusual molecular structure.

A 68-kD antigen, which is probably an N-terminal fragment of the VLA-5 alpha 5-subunit, is specific for differentiating keratinocytes

BACKGROUND

During terminal differentiation, basal keratinocytes lose gradually contact with the basement membrane, a process accompanied by the progressive functional down-regulation and loss of integrin expression. Understanding the molecular nature of this complex mechanism will eventually lead to insight into the pathogenesis of differentiation disorders of the epidermis, e.g. psoriasis.

OBJECTIVE

The monoclonal antibody 8D9 against the very late antigen 5 (VLA-5) integrin subunit was used to study the expression and down-regulation of this protein in several experimental paradigms of keratinocyte differentiation.

METHODS

Primary cultures of human keratinocytes were prepared and used as such, or after induction of terminal differentiation with methylcellulose and/or calcium. Expression of the 8D9 epitope was analyzed using immunoblotting, protein chemistry and immunocytochemistry on cultured cells and on skin biopsies from control and psoriatic patients.

RESULTS AND CONCLUSION

The monoclonal antibody 8D9 reacts with the alpha 5-subunit of human VLA-5 integrin and with a 68-kD antigen that is strongly expressed in differentiating keratinocytes in vitro and in the cornified layers of human skin in vivo. Psoriatic skin showed additional immunoreactivity in the upper spinous and granular layers. Based on indirect immunological and chemical evidence we suggest that the 68-kD protein is an amino-terminal degradation product of the alpha 5-subunit, which provides a new and interesting marker of differentiating keratinocytes.

Molecular cloning and characterization of the human interleukin-11 receptor alpha-chain gene, IL11RA, located on chromosome 9p13

The human gene coding for the interleukin-11 receptor (IL11RA) was cloned and its structure analyzed. The gene is composed of 13 exons comprising nearly 10 kb of DNA that was completely sequenced. The intron-exon boundaries were determined based on the mouse Etl2 and interleukin-11 receptor cDNAs that were recently cloned. The protein sequence predicted by the human gene was over 83% identical with its murine counterpart, with very strict conservation of functionally important domains and signatures. Fluorescence in situ hybridization showed the gene to be located on human chromosome 9p13, syntenic with the mouse etl2 gene on chromosome 4. The coding exons of the Interleukin-11 gene were sequenced in a patient with the cartilage-hair hypoplasia syndrome, which has been linked to a gene on chromosome 9, but no functional mutations were detected.

Exchanging the extracellular domain of amyloid precursor protein for horseradish peroxidase does not interfere with alpha-secretase cleavage of the beta-amyloid region, but randomizes secretion in Madin-Darby canine kidney cells

Secretory processing and polarized sorting of horseradish peroxidase fused to the amyloid precursor protein transmembrane domain were compared with those of wild-type amyloid precursor protein in COS and polarized Madin-Darby canine kidney (MDCK) cells. The cellular and secreted forms of the chimeric protein were enzymatically active in colorimetric and cytochemical assays after reconstitution with hemin and Ca2+. The peroxidase enzyme was secreted by a proteolytic process, similar to the parent amyloid precursor protein. In polarized MDCK cells, amyloid precursor protein was secreted exclusively in the basolateral compartment, while the peroxidase chimeric protein was secreted in both compartments. The basolateral sorting determinant for secretion must therefore be located in the extracellular domain of amyloid precursor protein. On the other hand, cell surface-associated peroxidase chimeric protein was similar to cell surface-associated wild-type amyloid precursor protein, mainly expressed at the basolateral side. The basolateral cell-surface expression, in contrast to the basolateral secretion, is therefore controlled by determinants in the cytoplasmic domain. Methylamine inhibited and bafilomycin slightly increased the basolateral secretion of both proteins, but both drugs strongly increased apical secretion. The default secretory pathway of COS cells and the basolateral (but not the apical) secretory pathway of MDCK cells are therefore comparably sensitive to methylamine and not to bafilomycin.

The seed lectins of black locust (Robinia pseudoacacia) are encoded by two genes which differ from the bark lectin genes

Two lectins were isolated from Robinia pseudoacacia (black locust) seeds using affinity chromatography on fetuin-agarose, and ion exchange chromatography on a Neobar CS column. The first lectin, R. pseudoacacia seed agglutinin I, referred to as RPsAI, is a homotetramer of four 34 kDa subunits whereas the second lectin, referred to as RPsAII, is composed of four 29 kDa polypeptides. cDNA clones encoding the polypeptides of RPsAI and RPsAII were isolated and their sequences were determined. Both polypeptides are translated from mRNAs of ca. 1.2 kb encoding a precursor carrying a signal peptide. Alignment of the deduced amino acid sequences of the different clones indicates that the 34 and 29 kDa seed lectin polypeptides show 95% sequence identity. In spite of this striking homology, the 29 kDa polypeptide has only one putative glycosylation site whereas the 34 kDa subunit has four of these sites. Carbohydrate analysis revealed that the 34 kDa possesses three carbohydrate chains whereas the 29 kDa polypeptide is only partially glycosylated at one site. A comparison of the deduced amino acid sequences of the two seed and three bark lectin polypeptides demonstrated unambiguously that they are encoded by different genes. This implies that five different genes are involved in the control of the expression of the lectins in black locust.

Molecular cloning of NIPP-1, a nuclear inhibitor of protein phosphatase-1, reveals homology with polypeptides involved in RNA processing

NIPP-1 was originally isolated as a potent and specific nuclear inhibitory polypeptide (16-18 kDa) of protein phosphatase-1. We report here the cDNA cloning of NIPP-1 from bovine thymus and show that the native polypeptide consists of 351 residues and has a calculated mass of 38.5 kDa. The bacterially expressed central third of NIPP-1 completely inhibited the type-1 catalytic subunit, but displayed a reduced inhibitory potency after phosphorylation by protein kinase A and casein kinase 2. Translation of NIPP-1 mRNA in reticulocyte lysates resulted in the accumulation of both intact NIPP-1 and a smaller polypeptide generated by alternative initiation at the codon corresponding to Met143. A data base search showed that the COOH terminus of NIPP-1 is nearly identical to the human ard-1 protein (13 kDa), which has been implicated in RNA processing (Wang, M., and Cohen, S. N. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 10591-10595). Comparison of the cDNAs encoding ard-1 and NIPP-1 suggests that their mRNAs are generated by alternative splicing of the same pre-mRNA. Western blotting with antibodies against the COOH terminus of NIPP-1, however, showed a single polypeptide of 47 kDa, which was enriched in the nucleus. Northern analysis revealed a single transcript of 2.2 kilobases in bovine thymus and of 2.4 kilobases in various human tissues.

A lectin and a lectin-related protein are the two most prominent proteins in the bark of yellow wood (Cladrastis lutea)

Using a combination of cDNA cloning and protein purification it is demonstrated that bark of yellow wood (Cladrastis lutea) contains two mannose/glucose binding lectins and a lectin-related protein which is devoid of agglutination activity. One of the lectins (CLAI) is the most prominent bark protein. It is built up of four 32 kDa monomers which are post-translationally cleaved into a 15 kDa and a 17 kDa polypeptide. The second lectin (CLAII) is a minor protein, which strongly resembles CLAI except that its monomers are not cleaved into smaller polypeptides. Molecular cloning of the Cladrastis lectin family revealed also the occurrence of a lectin-related protein (CLLRP) which is the second most prominent bark protein. Although CLLRP shows sequence homology to the true lectins, it is devoid of carbohydrate binding activity. Molecular modelling of the three Cladrastis proteins has shown that their three-dimensional structure is strongly related to the three-dimensional models of other legume lectins and, in addition, revealed that the presumed carbohydrate binding site of CLLRP is disrupted by an insertion of three extra amino acids. Since it is demonstrated for the first time that a lectin and a non-carbohydrate binding lectin-related protein are the two most prominent proteins in the bark of a tree, the biological meaning of their simultaneous occurrence is discussed.