Colocalization of cerebral iron with Amyloid beta in Mild Cognitive Impairment

Quantitative Susceptibility Mapping (QSM) MRI at 7 Tesla and 11-Carbon Pittsburgh-Compound-B PET were used for investigating the relationship between brain iron and Amyloid beta (Aβ) plaque-load in a context of increased risk for Alzheimer's disease (AD), as reflected by the Apolipoprotein E ε4 (APOE-e4) allele and mild cognitive impairment (MCI) in elderly subjects. Carriers of APOE-e4 with normal cognition had higher cortical Aβ-plaque-load than non-carriers. In MCI an association between APOE-e4 and higher Aβ-plaque-load was observable both for cortical and subcortical brain-regions. APOE-e4 and MCI was also associated with higher cortical iron. Moreover, cerebral iron significantly affected functional coupling, and was furthermore associated with increased Aβ-plaque-load (R²-adjusted = 0.80, p < 0.001) and APOE-e4 carrier status (p < 0.001) in MCI. This study confirms earlier reports on an association between increased brain iron-burden and risk for neurocognitive dysfunction due to AD, and indicates that disease-progression is conferred by spatial colocalization of brain iron deposits with Aβ-plaques.

Adolescent slipped capital femoral epiphysis treated by a modified Dunn osteotomy with surgical hip dislocation

Between June 2001 and November 2008 a modified Dunn osteotomy with a surgical hip dislocation was performed in 30 hips in 28 patients with slipped capital femoral epiphysis. Complications and clinical and radiological outcomes after a mean follow-up of 3.8 years (1.0 to 8.5) were documented. Subjective outcome was assessed using the Harris hip score and the Western Ontario and McMaster Universities osteoarthritis index questionnaire. Anatomical or near-anatomical reduction was achieved in all cases. The epiphysis in one hip showed no perfusion intra-operatively and developed avascular necrosis. There was an excellent outcome in 28 hips. Failure of the implants with a need for revision surgery occurred in four hips. Anatomical reduction can be achieved by this technique, with a low risk of avascular necrosis. Cautious follow-up is necessary in order to avoid implant failure.

Wound-induced apoplastic peroxidase activities: their roles in the production and detoxification of reactive oxygen species

Production of reactive oxygen species (ROS) is a widely reported response of plants to wounding. However, the nature of enzymes responsible for ROS production and metabolism in the apoplast is still an open question. We identified and characterized the proteins responsible for the wound-induced production and detoxification of ROS in the apoplast of wheat roots (Triticum aestivum L.). Compared to intact roots, excised roots and leachates derived from them produced twice the amount of superoxide (O2(*-)). Wounding also induced extracellular peroxidase (ECPOX) activity mainly caused by the release of soluble peroxidases with molecular masses of 37, 40 and 136 kD. Peptide mass analysis by electrospray ionization-quadrupole time-of-flight-tandem mass spectrometry (ESI-QTOF-MS/MS) following lectin affinity chromatography of leachates showed the presence of peroxidases in unbound (37 kD) and bound (40 kD) fractions. High sensitivity of O2(*-)-producing activity to peroxidase inhibitors and production of O2(*-) by purified peroxidases in vitro provided evidence for the involvement of ECPOXs in O2(*-) production in the apoplast. Our results present new insights into the rapid response of roots to wounding. An important component of this response is mediated by peroxidases that are released from the cell surface into the apoplast where they can display both oxidative and peroxidative activities.

What are the illness perceptions of people with dysphonia: a pilot study

Background: Patients do not respond to treatment in a predictable manner. Individual preconceptions determine help seeking, compliance and treatment outcome, yet clinicians rarely explore these issues. The illness perception approach sees the patient as an active participant in the healthcare process.

Aims: The aim of this study was to investigate the illness perceptions of people with dysphonia. The subsidiary aims were to correlate the Illness Perception Questionnaire with any psychological distress identified and a self-report measure of dysphonia, and to consider any potential implications for patient management.

Design: Prospective, cross-sectional observation.

Setting: Primary and secondary care, two general and four community hospitals.

Participants: Fifty adult patients with dysphonia due to benign disease completed three self-administered questionnaires, which investigated their illness perceptions, psychological distress and perceptions of the impact of the presenting ‘illness’.

Measures: The dysphonia was categorised as being due to functional (n=40) or organic (n=10) causes. All the voices were rated by an expert listener according to the GRBAS (grade, roughness, breathiness, aesthenia, strain) scale. Participants completed the Illness Perception Questionnaire, the Vocal Performance Questionnaire and the Hospital Anxiety and Depression scale.

Results: Patients showed a wide variation in perception of causation. They had no strong perceptions about the causes, consequences or duration of the presenting dysphonia. Functional dysphonics reported greater consequences, lower perceived control and increased anxiety when compared to patients with organic dysphonia. In terms of cure/control, all patients expected treatment to be helpful but this expectancy reduced as time increased. Anxiety was more associated with functional dysphonia, however, only 17 per cent of the subjects in this group showed clinically significant levels of signs of psychological distress.

Conclusions: Lay illness representations often diverge from the clinician's understanding of the presenting problem and strongly influence treatment behaviour. Early exploration of illness perceptions may enhance health behaviour and maximise the impact of intervention.

Incidence of enterohemorrhagic Escherichia coli, Escherichia coli O157, Salmonella, and Listeria monocytogenes in retail fresh ground beef, sprouts, and mushrooms

The objective of this study was to determine the prevalence of enterohemorrhagic Escherichia coli (EHEC), E. coli O157, Salmonella, and Listeria monocytogenes in retail food samples from Seattle, Wash. A total of 2,050 samples of ground beef (1,750 samples), mushrooms (100 samples), and sprouts (200 samples) were collected over a 12-month period and analyzed for the presence of these pathogens. PCR assays, followed by culture confirmation were used to determine the presence or absence of each organism. Of the 1,750 ground beef samples analyzed, 61 (3.5%) were positive for EHEC, and 20 (1.1%) of these were positive for E. coli O157. Salmonella was present in 67 (3.8%) of the 1,750 ground beef samples. Of 512 ground beef samples analyzed, 18 (3.5%) were positive for L. monocytogenes. EHEC was found in 12 (6.0%) of the 200 sprout samples, and 3 (1.5%) of these yielded E. coli O157. Of the 200 total sprout samples, 14 (7.0%) were positive for Salmonella and none were positive for L. monocytogenes. Among the 100 mushroom samples, 4 (4.0%) were positive for EHEC but none of these 4 samples were positive for E. coli O157. Salmonella was detected in 5 (5.0%) of the mushroom samples, and L. monocytogenes was found in 1 (1.0%) of the samples.

Laser speckle imaging with an active noise reduction scheme

We present an optical scheme to actively suppress statistical noise in Laser Speckle Imaging (LSI). This is achieved by illuminating the object surface through a diffuser. Slow rotation of the diffuser leads to statistically independent surface speckles on time scales that can be selected by the rotation speed. Active suppression of statistical noise is achieved by accumulating data over time. We present experimental data on speckle contrast and noise for a dynamically homogenous and a heterogeneous object made from Teflon. We show experimentally that for our scheme spatial and temporal averaging provide the same statistical weight to reduce the noise in LSI: The standard deviation of the speckle contrast value scales with the effective number N of independent speckle as 1/ radicalN.

Cloning of two thyrotropin-releasing hormone receptor subtypes from a lower vertebrate (Catostomus commersoni): functional expression, gene structure, and evolution

A PCR approach was used to clone thyrotropin-releasing hormone receptors (TRH-R) from the brain and anterior pituitary of the teleost Catostomus commersoni (cc), the white sucker. Two distinct TRH-R, designated ccTRH-R1 and ccTRH-R2, were identified. ccTRH-R1 was similar to mammalian TRH-R of the subtype 1, whereas ccTRH-R2 exhibited the highest identity (61% at the amino acid level) with the recently discovered rat TRH-R2. It is postulated that ccTRH-R2 and rat TRH-R2 are members of the same TRH-R subfamily 2. Functional expression of ccTRH receptors in human embryonic kidney cells and in Xenopus laevis oocytes demonstrated that both ccTRH receptors were fully functional in both systems. Oocytes expressing either receptor responded to the application of TRH by an induction of membrane chloride currents, indicating that ccTRH-R of both subtypes are coupled to the inositol phosphate/calcium pathway. The analysis of genomic clones revealed, for the first time, both similarities and differences in the structure of TRH-R subtype genes. Both ccTRH-R genes contained an intron within the coding region at the beginning of transmembrane domain (TM) 6. The position of this intron is highly conserved, as it was found at an identical position in the human TRH-R1 gene. The ccTRH-R2 gene contained an additional intron at the end of TM 3 that was not found in any of the TRH-R1 genes identified so far. The analysis of the gene structure of ccTRH-R and the amino acid sequence comparisons of mammalian and teleost TRH-R of both subtypes suggest that TRH receptors have been highly conserved during the course of vertebrate evolution. A common ancestral TRH receptor gene that could be found much earlier in evolution, possibly in invertebrates, might be the origin of ccTRH-R genes.

Synaptic scaffolding proteins in rat brain. Ankyrin repeats of the multidomain Shank protein family interact with the cytoskeletal protein alpha-fodrin

The postsynaptic density is the ultrastructural entity containing the neurotransmitter reception apparatus of excitatory synapses in the brain. A recently identified family of multidomain proteins termed Src homology 3 domain and ankyrin repeat-containing (Shank), also known as proline-rich synapse-associated protein/somatostatin receptor-interacting protein, plays a central role in organizing the subsynaptic scaffold by interacting with several synaptic proteins including the glutamate receptors. We used the N-terminal ankyrin repeats of Shank1 and -3 to search for interacting proteins by yeast two-hybrid screening and by affinity chromatography. By cDNA sequencing and mass spectrometry the cytoskeletal protein alpha-fodrin was identified as an interacting molecule. The interaction was verified by pull-down assays and by coimmunoprecipitation experiments from transfected cells and brain extracts. Mapping of the interacting domains of alpha-fodrin revealed that the highly conserved spectrin repeat 21 is sufficient to bind to the ankyrin repeats. Both interacting partners are coexpressed widely in the rat brain and are colocalized in synapses of hippocampal cultures. Our data indicate that the Shank1 and -3 family members provide multiple independent connections between synaptic glutamate receptor complexes and the cytoskeleton.

Vasopressin mRNA localization in nerve cells: characterization of cis-acting elements and trans-acting factors

mRNA localization is a complex pathway. Besides mRNA sorting per se, this process includes aspects of regulated translation. It requires protein factors that interact with defined sequences (or sequence motifs) of the transcript, and the protein/RNA complexes are finally guided along the cytoskeleton to their ultimate destinations. The mRNA encoding the vasopressin (VP) precursor protein is localized to the nerve cell processes in vivo and in primary cultured nerve cells. Sorting of VP transcripts to dendrites is mediated by the last 395 nucleotides of the mRNA, the dendritic localizer sequence, and it depends on intact microtubules. In vitro interaction studies with cytosolic extracts demonstrated specific binding of a protein, enriched in nerve cell tissues, to the radiolabeled dendritic localizer sequence probe. Biochemical purification revealed that this protein is the multifunctional poly(A)-binding protein (PABP). It is well known for its ability to bind with high affinity to poly(A) tails of mRNAs, prerequisite for mRNA stabilization and stimulation of translational initiation, respectively. With lower affinities, PABP can also associate with non-poly(A) sequences. The physiological consequences of these PABP/RNA interactions are far from clear but may include functions such as translational silencing. Presumably, the translational state of mRNAs subject to dendritic sorting is influenced by external stimuli. PABP thus could be a component required to regulate local synthesis of the VP precursor and possibly of other proteins.

Regulator of G protein signaling 4 suppresses basal and thyrotropin releasing-hormone (TRH)-stimulated signaling by two mouse TRH receptors, TRH-R(1) and TRH-R(2)

We cloned the mouse TRH receptor type 2 (mTRH-R2) gene, which is 92% identical with rat TRH-R2 and 50% identical with mTRH-R1 at the amino acid level, and identified an intron within the coding sequence that is not present in the TRH-R1 gene structure. Similar to its rat homolog, mTRH-R2 binds TRH with an affinity indistinguishable from mTRH-R1, signals via the phosphoinositide pathway like mTRH-R1, but exhibits a higher basal signaling activity than mTRH-R1. We found that regulator of G protein signaling 4 (RGS4), which differentially inhibits signaling by other receptors that couple to Gq, inhibits TRH-stimulated signaling via mTRH-R1 and mTRH-R2 to similar extents. In contrast, other RGS proteins including RGS7, RGS9, and GAIP had no effect on signaling by mTRH-R1 or mTRH-R2 demonstrating the specificity of RGS4 action. Interestingly, RGS4 markedly inhibited basal signaling by mTRH-R2. Inhibition of basal signaling of mTRH-R2 by RGS4 suggests that modulation of agonist-independent signaling may be an important mechanism of regulation of G protein-coupled receptor activity under normal physiologic circumstances.

Cloning of a gene for an acyl-CoA dehydrogenase from Pisum sativum L. and purification and characterization of its product as an isovaleryl-CoA dehydrogenase

Isovaleryl-CoA dehydrogenase (IVD, EC ) catalyzes the third step in the catabolism of leucine in mammals. Deficiency of this enzyme leads to the clinical disorder isovaleric acidemia. IVD has been purified and characterized from human and rat liver, and the x-ray crystallographic structure of purified recombinant human IVD has been reported. Nothing is known about IVD activity in plants, although cDNA clones from Arabidopsis thaliana and partial sequences from Gossypium hirsutum and Oryza sativa have been identified as putative IVDs based on sequence homology and immuno cross-reactivity. In this report we describe the identification and characterization of an IVD from pea, purification of the enzyme using a novel and rapid auxin affinity chromatography matrix, and cloning of the corresponding gene. At the amino acid level, pea IVD is 60% similar to human and rat IVD. The specific activity and abundance of plant IVD was found to be significantly lower than for its human counterpart and exhibits developmental regulation. Substrate specificity of the plant enzyme is similar to the human IVD, and it cross-reacts to anti-human IVD antibodies. Molecular modeling of the pea enzyme based on the structure of human IVD indicates a high degree of structural similarity among these enzymes. Glu-244, shown to function as the catalytic base in human IVD along with most of the amino acids that make up the acyl CoA binding pocket, is conserved in pea IVD. The genomic structure of the plant IVD gene consists of 13 exons and 12 introns, spanning approximately 4 kilobases, and the predicted RNA splicing sites exhibit the extended consensus sequence described for other plant genes.

Juxtamembrane regions in the third intracellular loop of the thyrotropin-releasing hormone receptor type 1 are important for coupling to Gq

Juxtamembrane residues in the putative third intracellular (I3) loops of a number of G protein-coupled receptors (GPCRs) have been shown to be important for coupling to G proteins. According to standard hydropathy analysis, the I3 loop of the mouse TRH receptor type 1 (mTRH-R1) is composed of 51 amino acids from position-213 to position-263. We constructed deletion and site-specific I3 loop TRH-R mutants and studied their binding and TRH-stimulated signaling activities. As expected, the effects of these mutations on TRH binding were small (less than 5-fold decreases in affinity). No effect on TRH-stimulated signaling activity was found in a mutant receptor in which the I3 loop was shortened to 16 amino acids by deleting residues from Asp-226 to Ser-260. In contrast, mutants with deletions from Asp-222 to Ser-260 or from Asp-226 to Gln-263 exhibited reduced TRH-stimulated signaling. In the region near transmembrane helix 6, single site-specific substitution of either Arg-261 or Lys-262 by neutral glutamine had little effect on signaling, but mutant TRH-Rs that were substituted by glutamine at both basic residues exhibited reduced TRH-stimulated activity. The reduced signaling activity of this doubly substituted mutant was reversed by over expressing the a subunit of Gq. These data demonstrate that the juxtamembrane regions in the TRH-R I3 loop are important for coupling to Gq.

Cloning and localization of C2orf2(ropp120), a previously unknown WD repeat protein

Ropp 120 (restrictedly overexpressed proliferation-associated protein) is a cytoplasmic protein of 120 kDa that is significantly overexpressed in mitotic cells. Protein sequencing of the immunoaffinity purified 120-kDa protein showed it to be an as yet unknown protein. DNA sequencing revealed a cDNA sequence of 3419 bases, which includes the complete coding region of ropp120 of 2943 bases (981 amino acids). Analysis of the deduced amino acid sequence showed that ropp 120 contains four WD repeats and a well-conserved consensus sequence of serine proteases. The gene encoding ropp120 (HGMW-approved gene symbol C2orf2) was assigned to chromosome 2p21-p22 by means of radiation hybrid and fluorescence in situ hybridization mapping.

Purification and molecular cloning of a novel essential component of the apolipoprotein B mRNA editing enzyme-complex

Editing of apolipoprotein B (apoB) mRNA requires the catalytic component APOBEC-1 together with "auxiliary" proteins that have not been conclusively characterized so far. Here we report the purification of these additional components of the apoB mRNA editing enzyme-complex from rat liver and the cDNA cloning of the novel APOBEC-1-stimulating protein (ASP). Two proteins copurified into the final active fraction and were characterized by peptide sequencing and mass spectrometry: KSRP, a 75-kDa protein originally described as a splicing regulating factor, and ASP, a hitherto unknown 65-kDa protein. Separation of these two proteins resulted in a reduction of APOBEC-1-stimulating activity. ASP represents a novel type of RNA-binding protein and contains three single-stranded RNA-binding domains in the amino-terminal half and a putative double-stranded RNA-binding domain at the carboxyl terminus. Purified recombinant glutathione S-transferase (GST)-ASP, but not recombinant GST-KSRP, stimulated recombinant GST-APOBEC-1 to edit apoB RNA in vitro. These data demonstrate that ASP is the second essential component of the apoB mRNA editing enzyme-complex. In rat liver, ASP is apparently associated with KSRP, which may confer stability to the editing enzyme-complex with its substrate apoB RNA serving as an additional auxiliary component.

Molecular heterogeneity of free PSA in sera of patients with benign and malignant prostate tumors

OBJECTIVE

To analyze free prostate-specific antigen (f-PSA) in sera from patients with prostate cancer (PCa) and benign prostatic hyperplasia (BPH), and to detect possible differences in subtypes as potential diagnostic parameters.

MATERIALS AND METHODS

PSA was purified from sera by an immunoaffinity procedure developed on the basis of oriented antibody immobilization, and subjected to size exclusion chromatography (SEC), Western blotting, and N-terminal amino acid sequencing.

RESULTS

The novel procedure allowed the purification of PSA with high yield from sera containing PSA <10 ng/ml. SEC under nonreducing conditions as well as Western blots demonstrated the presence of several molecular forms of f-PSA. Three of the smaller polypeptides exhibited the N-terminal sequence of PSA while one represented the C-terminal fragment Lys(146)-Pro(237). Shortening of some polypeptides by the N-terminal amino acid Ile(1) suggestive of aminopeptidase action was also observed. No propeptide sequence could be detected, and none of the bands from patient sera reacted with antibodies raised against propeptide antigens. BPH sera expressed higher proportions of smaller PSA fragments per unit p33, and contained significant amounts of fragments <14,000 which appeared to be very low or absent from most PCa sera.

CONCLUSIONS

f-PSA as obtained from BPH and PCa sera represents a heterogeneous fraction. The major component (p33) is not in the nicked form and does not contain proPSA. Diagnostic potential could arise from the quantitative differences of the smaller PSA derivatives seen between PCa and BPH sera.

Identification of melanin concentrating hormone (MCH) as the natural ligand for the orphan somatostatin-like receptor 1 (SLC-1)

To identify possible ligands of the orphan somatostatin-like receptor 1 (SLC-1), rat brain extracts were analyzed by using the functional expression system of Xenopus oocytes injected with cRNAs encoding SLC-1 and G protein-gated inwardly rectifying potassium channels (GIRK). A strong inward current was observed with crude rat brain extracts which upon further purification by cation exchange chromatography and high performance liquid chromatography (HPLC) yielded two peptides with a high agonist activity. Mass spectrometry and partial peptide sequencing revealed that one peptide is identical with the neuropeptide melanin concentrating hormone (MCH), the other represents a truncated version of MCH lacking the three N-terminal amino acid residues. Xenopus oocytes expressing the MCH receptor responded to nM concentrations of synthetic MCH not only by the activation of GIRK-mediated currents but also by the induction of Ca(2+) dependent chloride currents mediated by phospholipase C. This indicates that the MCH receptor can couple either to the G(i)- or G(q)-mediated signal transduction pathway, suggesting that MCH may serve for a number of distinct brain functions including food uptake behavior.

Neurotractin, a novel neurite outgrowth-promoting Ig-like protein that interacts with CEPU-1 and LAMP

The formation of axon tracts in nervous system histogenesis is the result of selective axon fasciculation and specific growth cone guidance in embryonic development. One group of proteins implicated in neurite outgrowth, fasciculation, and guidance is the neural members of the Ig superfamily (IgSF). In an attempt to identify and characterize new proteins of this superfamily in the developing nervous system, we used a PCR-based strategy with degenerated primers that represent conserved sequences around the characteristic cysteine residues of Ig-like domains. Using this approach, we identified a novel neural IgSF member, termed neurotractin. This GPI-linked cell surface glycoprotein is composed of three Ig-like domains and belongs to the IgLON subgroup of neural IgSF members. It is expressed in two isoforms with apparent molecular masses of 50 and 37 kD, termed L-form and S-form, respectively. Monoclonal antibodies were used to analyze its biochemical features and histological distribution. Neurotractin is restricted to subsets of developing commissural and longitudinal axon tracts in the chick central nervous system. Recombinant neurotractin promotes neurite outgrowth of telencephalic neurons and interacts with the IgSF members CEPU-1 (KD = 3 x 10(-8) M) and LAMP. Our data suggest that neurotractin participates in the regulation of neurite outgrowth in the developing brain.

Amino acid sequence of the D-galactose binding lectin II from the sponge Axinella polypoides (Schmidt) and identification of the carbohydrate binding site in lectin II and related lectin I

The sponge Axinella polypoides contains several D-galactose binding lectins. One of the main components, lectin I was sequenced earlier, the complete sequence of the other major constituent of saline extracts, lectin II has been determined by amino acid sequencing and mass spectrometry. Both lectins have a homology of 65% to each other and both possess a disulfide loop between positions 4 and 46. As long as this loop is closed in both lectins, they can be boiled in the presence of SDS or treated with 6 mol guanidine hydrochloride without losing their hemagglutinating activity. Incubation with beta-mercaptoethanol alone does not effect the carbohydrate binding capacity either. However, reduction of the disulfide bond under chaotropic conditions destroys the activity irreversibly. This disulfide loop is also an immunologically dominant epitope in both lectins, as was revealed with monospecific polyclonal antisera. Thus, sponge lectins seem to be of different origins, since three completely different structures were described: the structure of Geodia cydonium, related to the mammalian S-type lectins with one SH-group, the Axinella lectins with one disulfide loop and the Aaptos lectins I and II with 11 cysteine residues/subunit.

Identification of the integral membrane protein RM3/1 on human monocytes as a glucocorticoid-inducible member of the scavenger receptor cysteine-rich family (CD163)

The RM3/1 Ag is a membrane glycoprotein restricted to human monocytes and macrophages that evolve in the late phase of inflammation. Peptide sequence analysis of the RM3/1 protein revealed similarity to CD163, a member of the scavenger receptor cysteine-rich family. Using specific Abs (RM3/1, Ki-M8), we demonstrate an identical cellular regulation for the RM3/1 and the CD163 protein. Most notably, we show for the first time that CD163 is significantly up-regulated by glucocorticoids. In contrast, the protein is down-regulated by the immunosuppressant cyclosporin A and by phorbol esters, while the inflammatory mediator LPS has no significant influence on the expression. We describe the first isolation of a full-length cDNA of CD163 and expression of the corresponding protein. Several splice variants of CD163 exist, and we elucidated the kinetics of induction of three major mRNA splice variants by fluticasone propionate; another splice variant was proved to be unresponsive to this glucocorticoid. Taken together with a previous result showing an involvement of RM3/1 in adhesion of monocytes to the activated endothelium, we discuss that CD163 might play an important role in inflammatory processes.

Characterization, mapping and partial cDNA sequence of the 57-kD intracellular Ki-1 antigen

A novel antigen was identified by the cross-reactivity of the anti-CD30 antibody Ki-1. This 57-kD intracellular Ki-1 antigen (Ki-1/57) is induced upon activation of leukocytes and is transported to the nuclear compartment. We describe the partial cloning and sequencing of the Ki-1/57 cDNA from a lambda gt 11-cDNA library derived from the Hodgkin-analogous cell line L540. New monoclonal antibodies were produced against the recombinant Ki-1/57 protein fragment which were used to confirm that the Ki-1/57 antigen is associated with kinase activity and is expressed in a variety of tumor cell lines and in activated but not resting leukocytes. The Ki-1/57 gene was mapped to the bands 9q22.3-31 of human chromosome 9. This is an area which appears to be associated with secondary chromosomal aberrations in acute myeloid leukemias.

Elucidation of a new biological function of an old protein: unique structure of the cobra serum albumin controls its specific toxin binding activity

Although few proteins have been studies as thoroughly as serum albumin, a new biological property of this evolutionary ancient protein was recently discovered: The ability of cobra serum albumin (CSA) to specifically sequester lethal endogenous toxins. A study of the structural basis of this property is reported in this contribution. Two independent approaches were used to alter the structure of the CSA at defined positions: Directed mutagenesis and limited proteolysis. The conserved pattern of the disulfide linkages in the primary structure of the serum albumins showed in the case of the cobra snake (Naja naja kaouthia) an anomaly at C11 and C502, which suggested the existence of a unique spatial structure in this protein. The two cysteine residues were singly replaced with the consensus residue, i.e. C11-->F and C502-->T. The former substitution increased the specific neurotoxin binding capacity of the CSA by the factor 1.7 +/- 0.2, whereas the latter replacement reduced it to (25 +/- 2)%. The limited proteolysis yielded the large tryptic peptides T60, T40, T30 and T18, which after isolation by PAGE followed by HPLC had retained a strong toxin affinity. The location of these peptides in the amino-acid sequence was identified by Edman degradation and suggested the order of their release. On the basis of these data, a model of the unfolding and of the activity changes of the CSA caused by the structural perturbations was composed and the kinetic parameters associated with the process were evaluated. The results support the hypothesis of the existence of a structure of multiple homologous domains with a disulfide linkage between C11 and C502 in the native CSA that joins the chain ends to form a dense conformation.

Mitochondrial malate dehydrogenases in Brassica napus: altered protein patterns in different nuclear mitochondrial combinations

Two-dimensional analyses of mitochondrial proteins of Brassica napus revealed a set of differences in patterns of mitochondrial matrix proteins isolated from different nuclear backgrounds. One of these varying proteins was identified as mitochondrial malate dehydrogenase (mMDH;EC 1.1.1.37) by homology analyses of the partial amino acid sequence. Immunological detection identified additional mMDH subunits and detected different patterns of mMDH subunits in two distinct mitochondria types although they were isolated from plants with the same nuclear genotype. These differences are also reflected in isozym patterns, whereas Southern analyses showed no alteration in genome structure. Therefore mitochondria type-specific mMDH modifications are possible.

Exclusion of bioactive contaminations in Streptococcus pyogenes erythrogenic toxin A preparations by recombinant expression in Escherichia coli

The streptococcal erythrogenic exotoxin A (SPEA) belongs to the family of bacterial superantigens and has been implicated in the pathogenesis of a toxic shock-like syndrome and scarlet fever. Concerning its biological activity, mainly T-cell-stimulatory properties, conflicting data exist. In this study, we show that most of the SPEA preparations used so far contain biologically active contaminations. Natural SPEA from the culture supernatant of Streptococcus pyogenes NY-5 and recombinant SPEA purified from the culture filtrate of S. sanguis are strongly contaminated with DNases. We show that natural SPEA induces more tumor necrosis factor alpha (TNF-alpha) than recombinant SPEA, but we also show that DNases are able to induce TNF-alpha. In commercial SPEA preparations, we identified a highly active protease, which was shown not to be SPEB. To exclude these contaminations, we overexpressed SPEA cloned in the effective high-level expression vector pIN-III-ompA2 in Escherichia coli. The expressed SPEA shows the same amino acid composition as natural SPEA, whereas functional studies reported so far were carried out with toxins containing an incorrect amino terminus. We describe the rapid purification of lipopolysaccharide-, DNase-, and protease-free SPEA in two steps from the host's periplasm and its structural characterization by circular dichroism. Our results represent for the first time the production in E. coli of recombinant SPEA with the authentic N-terminal sequence and a proven superantigenic activity. Collectively, our results indicate that immunological studies of superantigens require highly purified substances free of biologically active contaminations.

UDP-glucose:sterol glucosyltransferase: cloning and functional expression in Escherichia coli

Steryl glucosides are characteristic lipids of plant membranes. The biosynthesis of these lipids is catalyzed by the membrane-bound UDP-glucose:sterol glucosyltransferase (EC 2.4.1.173). The purified enzyme (Warnecke and Heinz, Plant Physiol 105 (1994): 1067-1073) has been used for the cloning of a corresponding cDNA from oat (Avena sativa L.). Amino acid sequences derived from the amino terminus of the purified protein and from peptides of a trypsin digestion were used to construct oligonucleotide primers for polymerase chain reaction experiments. Screening of oat and Arabidopsis cDNA libraries with amplified labeled DNA fragments resulted in the isolation of sterol glucosyltransferase-specific cDNAs with insert lengths of ca. 2.3 kb for both plants. These cDNAs encode polypeptides of 608 (oat) and 637 (Arabidopsis) amino acid residues with molecular masses of 66 kDa and 69 kDa, respectively. The first amino acid of the purified oat protein corresponds to the amino acid 133 of the deduced polypeptide. The absence of these N-terminal amino acids reduces the molecular mass to 52 kDa, which is similar to the apparent molecular mass of 56 kDa determined for the purified protein. Different fragments of these cDNAs were expressed in Escherichia coli. Enzyme assays with homogenates of the transformed cells exhibited sterol glucosyltransferase activity.

p100: a novel proliferation-associated nuclear protein specifically restricted to cell cycle phases S, G2, and M

By immunization with nuclear lysates of L428 cells, we raised a monoclonal mouse antibody, Ki-S2 (IgG1). In Western blots, this antibody recognizes a nuclear antigen with an apparent molecular mass of 100 kD, termed p100. Protein sequencing of p100 showed that this is a hitherto unknown protein. Immunohistochemical examination of cryostat and paraffin sections of nearly all human tissue types and neoplasms showed that p100 was exclusively expressed in the nuclei of a fraction of proliferating cells. Cell sorting and fluorescence-activated cell sorting analysis of stimulated peripheral blood mononuclear cells showed that p100 was exclusively expressed in proliferating cells from the transition G1/S until the end of cytokinesis. During mitosis, this protein is strictly associated with the spindle pole and with the mitotic spindle, whereas during S and G2, p100 is diffusely distributed throughout the cell nucleus. Immediately after completion of cytokinesis, p100 was rapidly degraded. In L428 cells, p100 is phosphorylated at least during mitosis. It has a turnover time of about 1 hour. Studies on routinely processed paraffin sections of specimens of malignant lymphoma, benign and malignant nevocellular tumors, and breast cancer showed that in all cases less than 40% of the Ki-67-positive growth fraction expressed p100. Thus, p100 might prove to be a more reliable measure of cellular proliferation and one that is more closely correlated to cancer prognosis, beyond its general biologic relevance as a cell cycle protein.

Purification of a head-activator receptor from hydra

Head activator (HA) is a neuropeptide conserved from hydra to humans. It acts in the development of neuronal cells and is, in hydra, an important factor in head regeneration. Here we report the solubilization and purification of one head activator receptor (Kd approximately 1 nM) from a multiheaded mutant of Chlorohydra viridissima using HA affinity chromatography. Functional solubilization of the HA receptor from hydra membranes was best performed with Triton X-100 or Chaps. The addition of salt or urea and the protein concentration were important parameters in determining the yield of solubilized receptor. For affinity chromatography HA was coupled to Sepharose. The length of the spacer was optimized with respect to binding of the solubilized HA receptor. After rigorous washing a 200-kDa protein was eluted from HA Sepharose but not from control Sepharoses coupled to bradykinin or without peptide. Ligand binding was preserved in the eluate from the HA Sepharose, and a 200-kDa protein could be photoaffinity labeled. The 200-kDa protein was shown to be glycosylated mainly of the N-linked type. By Edman degradation of the purified protein sequence information was obtained for the N-terminus and after protease digestion for several internal peptides.

The human factor H-related protein 4 (FHR-4). A novel short consensus repeat-containing protein is associated with human triglyceride-rich lipoproteins

A novel apoprotein of an apparent molecular mass of 86 kDa in its unreduced form was identified in human triglyceride-rich lipoproteins. This protein was purified and the amino acid sequence of six proteolytic fragments was found to overlap with that of the factor H-related proteins. In parallel we identified the cDNA encoding a new complement factor H-related protein, termed FHR-4. The sequences of the new apoprotein overlapped with that of the FHR-4 protein. Similar to the previously described factor H-related proteins, FHR-4 contains a hydrophobic signal sequence followed by a stretch of five repetitive elements termed short consensus repeats. Recombinant FHR-4 protein was expressed in the baculovirus system and has an apparent molecular mass of 42 kDa. In addition a 84-kDa dimeric form of the recombinant FHR-4 was detected. Using an immunoaffinity column with antibodies raised against the recombinant FHR-4, we isolated a 86-kDa protein from human plasma. The different molecular mass of the recombinant FHR-4 and the dimeric FHR-4 in plasma is due to different carbohydrate moieties. The 86-kDa plasma protein and the novel apolipoprotein had identical mobility on SDS-polyacrylamide gel electrophoresis analysis and reacted with antisera raised against the reFHR-4 and the purified apoprotein. In conclusion, we have identified a novel factor H-related protein, FHR-4, in human plasma and demonstrate that this protein is present in triglyceride-rich lipoproteins in a dimeric form. This observation provides an intriguing new aspect on possible function(s) of this novel protein and the other factor H-related proteins.

Chicken acidic leucine-rich EGF-like domain containing brain protein (CALEB), a neural member of the EGF family of differentiation factors, is implicated in neurite formation

Chicken acidic leucine-rich EGF-like domain containing brain protein (CALEB) was identified by combining binding assays with immunological screens in the chicken nervous system as a novel member of the EGF family of differentiation factors. cDNA cloning indicates that CALEB is a multidomain protein that consists of an NH2-terminal glycosylation region, a leucine-proline-rich segment, an acidic box, a single EGF-like domain, a transmembrane, and a short cytoplasmic stretch. In the developing nervous system, CALEB is associated with glial and neuronal surfaces. CALEB is composed of a 140/130-kD doublet, an 80-kD band, and a chondroitinsulfate-containing 200-kD component. The latter two components are expressed in the embryonic nervous system and are downregulated in the adult nervous system. CALEB binds to the extracellular matrix glycoproteins tenascin-C and -R. In vitro antibody perturbation experiments reveal a participation of CALEB in neurite formation in a permissive environment.

Detection of human topoisomerase II alpha in cell lines and tissues: characterization of five novel monoclonal antibodies

We report five novel monoclonal antibodies (Ki-S1, Ki-S4, Ki-S6, Ki-S7, and Ki-S8) reactive with a proliferation-related nuclear antigen. In immunoprecipitation and Western blot experiments using crude nuclear extracts, they recognized a protein of 170 kD that, after proteolytic digestion of the immunoprecipitate and sequencing of the resulting peptides, was identified as the alpha-isoform of human topoisomerase II. This was confirmed by testing the antibodies on a highly purified enzyme preparation. Crossreactivity with topoisomerase II beta was ruled out by testing the antibodies on crude extracts from yeast cells expressing the beta-isoform exclusively. The antibodies bind the antigen with different affinities and at different epitopes, apparently located within the carboxyl third of the enzyme. All five antibodies are suitable for archival material after adequate antigen retrieval, thereby enabling retrospective studies. This report illustrates the tissue and subcellular distribution of the antigen through the cell cycle by immunohistochemistry and confocal fluorescence microscopy. The antibodies will be useful tools in further analysis of morphological and functional aspects of topoisomerase II and may serve diagnostic purposes, as well as providing prognostic information in tumor pathology.

Cytokinin affects nuclear- and plastome-encoded energy-converting plastid enzymes

Cytokinins induce two specific morphological alterations in mosses: (i) the differentiation of a tip-growing cell into a three-faced apical cell (the so-called bud), and (ii) the division of chloroplasts. In a developmental mutant of the moss Physcomitrella patens (Hedw.) B.S.G. (mutant PC22) impeded in both cellular differentiation (bud production) and chloroplast division, addition of cytokinin (N6-delta 2-isopentenyladenine) led to bud production after 3 d in the wild type and after 7 d in the mutant. Hormone induced a division of the mutant macrochloroplasts starting within 24 h and ongoing for 72 h. During this period the abundances of several plastid proteins changed in both genotypes as judged by two-dimensional-protein gel electrophoresis, silver staining and subsequent quantification with novel computer software. Eight of these polypeptides were isolated independently, subjected to microsequencing and thus identified, resulting in the first protein sequence data from a moss. Three polypeptides (24 kDa, 22 kDa, 20 kDa) were found to be homologous to enhancer protein OEE2 of the oxygen-evolving complex, four to represent isoforms of phosphoglycerate kinase (EC 2.7.2.3), and one was identified as the beta-chain of chloroplast ATPase (EC 3.6.1.34). Possible involvement of these key enzymes of the chloroplast energy-conversion machinery in organelle division and in cellular differentiation is discussed. Further sequence information was obtained from both subunits of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39). Amounts of these polypeptides were not appreciably affected by cytokinin in moss chloroplasts.

Monoclonal antibodies Ki-S3 and Ki-S5 yield new data on the 'Ki-67' proteins

The monoclonal antibody (mab) Ki-67 has been used for about 10 years, mainly in tissue sections, to monitor proliferating cells, but so far only very little is known about the proteins it recognizes. The new mabs Ki-S3 and Ki-S5 detect proliferating cells in frozen and paraffin-embedded tissues. They recognize proteins with the same molecular mass as Ki-67 in Western blot and for the first time also in immunoprecipitation experiments. With these mabs we were able to enrich and purify the Ki-67 proteins. Protein sequencing of four peptides of the digested proteins corresponded to the cDNA-deduced amino acid sequence already published for the Ki-67 proteins. Since we were able to immunoprecipitate the Ki-67 proteins, we performed various immunoprecipitation experiments to obtain more information about the nature of these proteins. After radiolabelling L428 cells with [35S]-methionine we were able to immunoprecipitate the Ki-67 proteins after only 5 min of labelling time. In turnover experiments the Ki-67 proteins could not be detected 3 h after the end of labelling. These data indicate a half-life of the Ki-67 proteins of about 90 min. Labelling experiments with [32P]-orthophosphate revealed that the Ki-67 proteins are phosphorylated. After dephosphorylation was blocked with okadaic acid or cell growth was arrested by means of Colcemid, the phosphorylation of the Ki-67 proteins was greatly increased, indicating that the Ki-67 proteins are phosphorylated via serine and threonine, and that the phosphorylation of the Ki-67 proteins increases in cycling cells. Labelling experiments with [3H]-mannose and [3H]-glucose revealed that the protein is weakly N-glycosylated.

Vaccination and mucosal responses to Helicobacter pylori infection

H. pylori infection persists for life if not treated, and is responsible for major morbidity and mortality throughout the world. Preventative immunization, once thought to be impossible, is now considered by many to be the only practical approach to large-scale elimination of the bacterium from susceptible populations. High rates of protection have been achieved in the H. felis mouse model, utilizing antigens ranging from whole cells to purified recombinant proteins selected on the basis of their role in pathogenicity. Immunization has also been shown to cure established infection. H. pylori mouse models have been developed and may become the model of choice. Urease remains the favourite antigen but combinations will most likely be required. A priority is to define alternate muscosal adjuvants, as some used in the animal models may be too toxic for use in humans. Also, there is a need to understand the basis of immunization. Why does the natural immune response to H. pylori fail while the artificially stimulated response succeeds? The first important steps towards a vaccine have been made but, given safety issues and regulatory requirements, it may be 5-8 years before the final product becomes available. Over these years antimicrobial resistance is likely to be an increasing problem in the treatment of H. pylori infections. Thus, when the vaccine comes, the time will be ripe for the completely new approach of therapeutic immunization.

Isolation of the myc transcription factor nucleoside diphosphate kinase and the multifunctional enzyme glyceraldehyde-3-phosphate dehydrogenase by cAMP affinity chromatography

Cyclic AMP affinity chromatography applied to various mammalian tissue extracts yielded two proteins in addition to the regulatory subunits of protein kinase. This paper characterizes these proteins and provides a simple procedure for their preparation. The polypeptides (36 kDa and a 19 kDa/21 kDa doublet) were isolated from the cAMP matrix by sequential elution with cAMP solutions of increasing concentrations. Microsequencing was accomplished following chemical or enzymic degradation of isolated polypeptides. Partial amino acid sequences of the 36 kDa protein and analyses of its enzymic activity indicated identity with glyceraldehyde-3-phosphate dehydrogenase whilst the lower MW protein proved to be identical with mammalian nucleoside diphosphate kinase subunits. In both cases, binding to cAMP appeared to occur at the nucleotide (NAD and ATP, respectively) sites. In conclusion, we present a one step-procedure, applicable to tissue and cell extracts, which allows the simultaneous isolation of both glyceraldehyde-3-phosphate dehydrogenase and nucleoside diphosphate kinase. This procedure may help to elucidate the multiple functions of these two important enzymes.

Purification and PCR-based cDNA cloning of a plastidial n-6 desaturase

A plastidial membrane-bound n-6 desaturase from spinach (Spinacia oleracea) was purified from chloroplast envelope membranes by anion exchange, cation exchange and ferredoxin-affinity chromatography. The molecular mass of the protein was estimated by SDS-PAGE to be 40 kDa. The highest specific activity of the desaturase in the final preparation was 196 nmol/min per mg protein with free oleic acid as the substrate. The N-terminal amino acid sequence of the blotted protein was determined and used for the construction of a degenerated and inosine-containing oligonucleotide primer for PCR experiments with cDNA transcribed from leaf mRNA. A 3'-RACE experiment with this primer amplified a single band of 1500 bp that after sequencing showed an open reading frame of 382 amino acids corresponding to a protein of 43 kDa. The 5' end of the cDNA was amplified by a 5'-RACE experiment and isolated as a 500 bp fragment. Sequencing of this DNA revealed an additional 65 amino acids at the N-terminus of the native protein that are attributed to a plastidial leader peptide. With appropriate primers derived from these sequences a full-length clone was amplified by PCR and sequenced. Comparison of the plastidial oleate desaturase with the homologous enzyme from cyanobacteria showed about 50% amino acid homology. Comparison with other desaturases revealed three histidine boxes with the general sequence HXXXH that are highly conserved in all membrane-bound desaturases. These boxes might be involved in metal ion complexation required for reduction of oxygen.

Chicken MAR binding protein p120 is identical to human heterogeneous nuclear ribonucleoprotein (hnRNP) U

We have previously identified two proteins from chicken oviduct nuclei that specifically bind to matrix/scaffold attachment regions (MARs/SARs). Here one of these proteins, named p120 due to its apparent molecular weight, is purified to near homogeneity and shown to be identical to a previously described component of heterogeneous nuclear ribonucleoprotein particles, hnRNP U, on the basis of amino acid sequence analysis of tryptic peptides. p120 binds to multiple MAR fragments provided they have a minimal length of approximately 700 bp. Binding of MAR fragments is specifically competed by homoribopolymers poly(G) and poly(I), which form four-stranded structures. Our results suggest that p120/hnRNP U may serve a dual function, first as a component of hnRNP particles, and second as an element in the higher-order organization of chromatin.

Annexin VI, a marker protein of hepatocytic endosomes

Three highly purified endosomal fractions from rat liver were used to purify and characterize a major protein of endosomal membranes. Intravenously injected ligands, which are taken up via receptor-mediated endocytosis, accumulate first in the fraction of intermediate density, the compartment of uncoupling of receptors and ligands. The high density membranous fraction is highly enriched in a receptor recycling compartment. The endosomal fraction of lowest density is composed of multivesicular bodies, which appear to be the immediate prelysosomal compartment. The most prominent membrane protein of these endosomes is one of 68 kDa, as revealed by silver and Coomassie Brilliant Blue staining of SDS-gel electrophoretograms. This protein dominates profiles obtained from purified membranes of the compartment of uncoupling of receptors and ligands, multivesicular bodies, and receptor recycling compartment, but is greatly reduced in those obtained from plasma membranes and lysosomes. The 68-kDa protein was purified from endosomes and digested with trypsin, and cleavage products were analyzed by protein sequencing. The tryptic fragments of the endosomal 68-kDa protein share 96% identity with corresponding sequences of mouse annexin VI and 91% identity with sequences of human annexin VI. Using immunoblots, high concentrations of annexin VI with an apparent molecular mass of 68 kDa were detected in endosomal membranes by specific antiserum to annexin VI. Significant amounts of annexin VI were also detected in Golgi membranes. Yet, the concentration was substantially lower than that of the three endosomal fractions. The association of annexin VI with endosomal membranes is calcium-dependent, as revealed by the complete solubilization from endosomal membranes by EGTA. Incubation of intact endosomes with Pronase leads to a complete degradation of annexin VI without any detectable disintegration of proteins localized on the luminal surface of endosomal membranes. Evidently, annexin VI is localized on the cytoplasmatic leaflet of the membrane of endosomes and may be of significance for their intracellular trafficking.

Molecular cloning of human von Ebner's gland protein, a member of the lipocalin superfamily highly expressed in lingual salivary glands

Von Ebner's glands (VEG) are small lingual salivary glands. Their ducts open into trenches of circumvallate and foliate papillae, thus influencing the milieu where the interaction between taste receptor cells and sapid molecules takes place. The major secretions of human VEG is a protein with a molecular mass of 18 kDa. The human VEG protein crossreacts with antibodies raised against the rat VEG protein, indicating sequence similarity between the rat and human VEG proteins. This was subsequently confirmed by N-terminal protein sequencing. A cDNA clone, isolated from a human VEG library, contained an insert of 735 bp including an open reading frame that encodes the human VEG protein of 176 amino acids. Comparison of the human and rat VEG proteins revealed an overall identity of 60%. Immunocytochemistry, in situ hybridization and in vitro translation studies demonstrated the human VEG protein to be highly and exclusively expressed in VEG. The VEG proteins are members of the lipocalin protein superfamily and, together with the rat odorant binding protein II, they constitute a new subfamily. Sequence similarity to proteins such as the retinol binding protein and the odorant binding protein which are lipophilic ligand carriers, suggests a possible function for the human VEG protein in taste perception.

Epigenetic activation of Gi-2 protein, the product of a putative protooncogene, mediates tumor promotion in vitro

Promotion of 'initiated' JB6 epidermal cells to the tumor phenotype can be effected by 12-O-tetradecanoylphorbol-13-acetate treatment, by stimulation of epidermal growth factor (EGF) receptor activity with EGF or transforming growth factor alpha and by exposure to the isoquinoline derivative H7. When these cells were incubated with pertussis toxin (PTX), induction of anchorage-independent growth by all four promoting substances was suppressed. The inhibition is specific since cell proliferation is not affected, suggesting that activation of a Gi protein is essential for promotion of the epidermal cells. This interpretation is strongly supported by the observation that the wasp poison mastoparan, which is known to mimic receptor-mediated activation of certain Gi proteins, also promoted anchorage independence. Immunological data and partial amino acid sequence analysis of ADP-ribosyl alpha i isolated from PTX-treated JB6 cells indicate that a Gi-2 protein is a mediator to tumor promotion in this system. The inhibitory action of 4-bromophenacyl bromide may point to a coupling of the Gi protein to phospholipase A2. From our data we infer that promoters induce the tumor phenotype in 'initiated' JB6 epidermal cells by activating epigenetically the same Gi protein that in a number of adrenal and ovarian tumors appears to be persistently activated by mutational events.

Rat insulin-degrading enzyme: cleavage pattern of the natriuretic peptide hormones ANP, BNP, and CNP revealed by HPLC and mass spectrometry

The degradation of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP) by insulin-degrading enzyme (IDE) has been investigated. As revealed by high-performance liquid chromatography, all three peptides are sequentially cleaved at a limited number of sites, the latter of which were identified by mass spectrometric analyses. The studies revealed that ANP is preferred as substrate over BNP and CNP. ANP degradation is rapidly initiated by hydrolysis at the Ser25-Phe26 bond. Three additional cleavage sites were identified in ANP after prolonged incubation with IDE; in contrast, three and two bonds were hydrolyzed in BNP and CNP, respectively. Analysis of the nine cleavage sites shows a preference for basic or hydrophobic amino acid residues on the carboxyl side of a cleaved peptide bond. In contrast to most of the peptide fragments generated by IDE activity, the initial ANP cleavage product, F-R-Y, is rapidly degraded further by cleavage of the R-Y bond. Cross-linking studies with 125I-ANP in the presence of sulfhydryl-modifying agent indicate that IDE activity is inhibited at the level of initial substrate binding whereas metal-ion chelating agents only prevent hydrolysis. On the basis of its structural and enzymatic properties, IDE exhibits striking similarity to a number of recently-described endopeptidases.

Comparative investigations on the amino-acid sequences of different isolectins from the sponge Axinella polypoides (Schmidt)

The sponge Axinella polypoides contains four different D-galactose binding lectins and one, termed lectin IV, which is specific for hexuronic acids. Only the D-galactose binding lectins were investigated in this study. The complete amino-acid sequence of lectin I, the main component in the crude extract was determined. Lectin I is a homodimer and each subunit comprises 144 amino acids with a M(r) of 15,847 +/- 10, as calculated from the sequence data and determined by mass spectrometry. Each subunit contains one intrachain disulfide bridge between positions 4 and 46. Of lectin II, only the first 49 amino acids of the NH2-terminal end were analysed. This part has 29 amino acids in common with lectin I, including a cysteine residue at position 4, also suggesting an intrachain loop in a identical position as in lectin I. The molecular mass of its subunit is 16,235 +/- 10 Da. Only the first 15 NH2-terminal amino acids of lectins III and V could be sequenced. Lectin V was identical to lectin II in all positions, whereas lectin III showed only 5 residues identical to lectins I or II. Thus, lectins I, II and III are derived from three different genes, whereas lectin V may either be a proteolytic cleavage product, or result from different splicing events or may be derived also from a separate gene. Neither of the four lectins showed any similarity to known lectin sequences of animal or plant origin.