Curative Radiotherapy for Locally Advanced Scalp Squamous Cell Carcinoma

A 73-year-old man presented to his primary physician with an ulcerative growth on his scalp vertex. Biopsy of the lesion confirmed the growth to be a moderately differentiated squamous cell carcinoma, but the patient declined medical intervention. The lesion increased in size over six months, measuring 12 cm in diameter and 3 cm thickness with erosion of the skull of the vertex. CT and MRI scans showed a large fungating mass with erosion of the skull of vertex without intra-cranial extension, meningeal enhancement, or distant metastatic disease. The patient declined surgical intervention. The patient received radiotherapy using volumetric-modulated arc therapy (VMAT) to a total dose of 60 Gy over six weeks. No evidence of clinical invasive disease apart from a 15 cm * 12 cm skin defect detected three months after completion of radiotherapy. At three years of follow-up, the patient is clinically disease-free. This case report provides evidence that high-dose radiotherapy is a potential effective definitive treatment for locally advanced (T4) squamous cell carcinoma for patients who are unwilling to undergo surgery.

Spatial prediction of soil depth using environmental covariates by quantile regression forest model

Prediction of soil depth for larger areas provides primary information on soil depth and its spatial distribution that becomes vital for land resource management, crop, nutrient, and ecosystem modeling. The present study assessed the spatial distribution of soil depth over 160,205 km² of Andhra Pradesh, India, using 20 covariables by quantile regression forest (QRF). An aggregate of 2854 soil datasets compiled from various physiographic units were randomly partitioned into 80:20 ratio for calibration (2283 samples) and validation (571 samples). Landsat imagery, terrain datasets (8), and bioclimatic factors (11) were utilized as covariates. The QRF model outputs signified that precipitation, multi-resolution index of valley bottom flatness (MrVBF), mean diurnal range, isothermality, and elevation were the most important variables influencing soil depth variability across the landscape. Spatial prediction of soil depth by QRF model yielded a ME of - 1.81 cm, RMSE of 34 cm, PICP of 90.2, and a R² value of 42% as compared to ordinary kriging which results in a ME of - 0.14 cm, a RMSE of 37 cm, and a R² value of 32%. As soil depth is spatially dynamic and has significant correlation with terrain and environmental covariates, better prediction was possible by the QRF model. However, high-density bioclimatic variables could be utilized along with high-resolution terrain variables to improve the predictive accuracy.

Hydrochemical characterization and groundwater quality in Cauvery deltaic fluvial plains of Southern India

Groundwater sources are drastically changing in their quantity and quality depending on local and regional level natural and anthropogenic factors, influencing their suitability for drinking and irrigation purposes. The objective of this study is to characterize the hydrochemistry and assess the groundwater quality in the fluvial deltaic plains of Cauvery river basin, Tamil Nadu, India. A total of 50 georeferenced groundwater samples were collected across Needamangalam block of Thiruvarur district and analyzed for major ions and hydrochemical processes. The results showed an ionic sequence of Cl^- > Na⁺ > HCO₃^- > Mg²⁺ > Ca²⁺ > CO₃^2- > SO₄^2- > K⁺ based on their relative proportions. The scatter diagram indicated that groundwater chemistry was mostly influenced by weathering dominance followed by evaporation and silicate weathering. The dominant hydro-chemical facies were Na⁺-Cl^--HCO₃^- type, Na⁺-Mg²⁺-Cl^--HCO₃^- type, Na⁺-Cl^--HCO₃^--CO₃^2- type and Na⁺-Mg²⁺-Cl^--HCO₃^--CO₃^2- type influenced by the ion-exchange reaction. Most of the groundwater samples are suitable for drinking and irrigation except few with higher Na⁺ and Cl^- content caused by the mixing of salt from fluvio-marine sources or agriculture return flow. The high sodium content in irrigation water may affect the soil hydraulic and nutrient properties in the long run.

Assessment of asthma control in users of oral anti-asthma medications

BACKGROUND: Despite guidelines recommending inhalation therapy as the preferred choice, oral therapy is still widely used in the treatment of asthma in India. However, data about the level of asthma control and healthcare use in patients on oral anti-asthma medications are scarce.METHODS: A retrospective study was conducted to assess the level of asthma control and healthcare use in patients taking oral anti-asthma medications.RESULTS: The study population consisted of 381 adults randomly selected from health screening programmes. All subjects were already receiving oral anti-asthma medications; however, up to 72% had not been diagnosed with asthma by their treating doctors prior to the screening programmes. The cohort had a mean age of 48.26 ± 13.83 years (70% males) and mean peak expiratory flow of 245 ± 78.93 mL/sec. The mean Asthma Control Questionnaire 5 (ACQ-5) score was 2.53 ± 1.15, with respectively 33%, 49.3% and 32.6% reporting at least one episode of breathlessness, one emergency doctor visit and one hospitalisation due to asthma or its symptoms in the past year.CONCLUSION: Underdiagnosis and inappropriate management, as indicated by the poor asthma control and increased hospitalisations seen in this study, is probably a key contributor to the increased burden of the disease in India.

Successful Treatment of Malignant Priapism by Radiotherapy: Report of a Case, Review of the Literature, and Treatment Recommendations

Malignant priapism is a condition of painful induration and erection of the penis secondary to metastatic infiltration by a neoplasm. This condition is associated with a poor prognosis. We report on a case of an 87-year-old man who presented with a painful, partially erected penis subsequent to a diagnosis of metastatic Gleason 4+5 prostate cancer. Magnetic resonance imaging (MRI) showed diffuse bilateral infiltration of his corpora cavernosa. The core biopsy of the penile nodule revealed it to be a poorly differentiated carcinoma consistent with prostatic origin. The patient's symptoms were completely resolved after treatment with high-dose palliative conformal radiotherapy (40Gy in 16 fractions). We systemically reviewed clinical reports of palliative radiotherapy for malignant priapism with the aim to gain more information on the management of this rare condition.

NeeMDB: Convenient Database for Neem Secondary Metabolites

Indian Neem tree is known for its pesticidal and medicinal properties for centuries. Structure elucidation of large number of secondary metabolites responsible for its diverse properties has been achieved. However, this data is spread over various books, scientific reports and publications and difficult to access. We have compiled and stored structural details of neem metabolites in NeeMDB, a database which can be easily accessed, queried and downloaded. NeeMDB would be central in dissipating structural information of neem secondary metabolites world over.

Spatial and temporal volatile organic compound response of select tomato cultivars to herbivory and mechanical injury

Plants resist an insect or pathogen attack through a range of direct and indirect defense signals. Vegetable crop plants constitutively synthesize and store a battery of volatiles implicated in defense against herbivores. We examined the effect of herbivory (Spodoptera litura Fab.) and mechanical injury on the release of volatile organic compounds (VOCs) in five tomato (Solanum lycopersicum Mill.) cultivars followed by behavioral assays on Trichogramma chilonis Ishii. T. chilonis is an egg parasitoid widely used as biocontrol agent in integrated pest management practices. Our goal was to assess the VOC variability across cultivars under different induction regimes. The findings reveal variability among cultivars in the absolute quantity of VOCs emitted as well as qualitative composition of the blend. Herbivore and mechanical wounding caused a substantial quantitative shift in the emission profile of select cultivars. The uninduced and induced volatiles of the tomato cultivars predominantly constitute monoterpenes (65%) followed by sesquiterpenes (15%) and aldehydes (10%). These ubiquitous and induced signals triggered a distinct cultivar specific olfactory response in T. chilonis. The spatial and temporal variations in induced VOCs across tomato cultivars suggest that these unique metabolite profiles are largely intrinsic and genetically determined. This study highlights the genotype based volatile profile and indicates their potential role in host, pest and natural enemy interactions.

RURS' elbow guard: an innovative treatment of the thumb-sucking habit in a child with Hurler's syndrome

Thumb sucking is the process of sucking on the thumb for oral pleasure. Thumb and finger sucking habits, or nonnutritive sucking, are considered to be the most prevalent of oral habits. Some parents are concerned by thumb sucking and may even try to restrain the infant or child. In most cases, this is not necessary. Most children stop thumb sucking on their own. When older children continue to suck their thumbs, it could mean they are bored, anxious, or have emotional problems such as depression. This article presents a case report of a child with Hurler's syndrome along with thumb sucking/biting habit. Hurler's syndrome, also known as mucopolysaccharidosis I, is a rare condition inherited as an autosomal-recessive trait. It represents the classical prototype of mucopolysaccharide disorder. A unique appliance to prevent thumb sucking/biting was developed and termed as "RURS' elbow guard," which was successfully used to break thumb sucking of the child with Hurler syndrome. The present report also describes the steps in fabrication of this new habit-breaking appliance, which is also designed to protect the finger from the effects of the sucking habit.

Autonomic dysfunction in tetanus - what lessons can be learnt with specific reference to alpha-2 agonists?

Severe tetanus is seen infrequently in the developed world, but often requires intensive care support. Mechanical ventilation with neuromuscular blockade and heavy sedation, good wound care and prompt administration of antitoxin are important. The management of autonomic dysfunction remains challenging. We measured serum catecholamine levels in a patient with severe tetanus in whom autonomic crises were a major and persistent feature, and investigated the impact of sedatives plus alpha(2)-agonists on these levels. Serum adrenaline levels were elevated up to 100-fold with clinically observed crises, although noradrenaline levels were much more difficult to interpret. There was no appreciable difference in catecholamine levels following administration of alpha(2)-agonists in the doses we used, although clonidine did allow easier control of crises with other agents. This case highlights some important lessons in the management of severe tetanus.

The Jehovah's Witness and dementia: who or what defines 'best interests'?

An elderly woman with dementia presented for repeat surgical management of fractured neck of femur. Although no advance directive had ever been generated, the patient was declared to be a strict Jehovah's Witness by her daughter, who vetoed the transfusion of any blood products. The fracture was managed conservatively but the patient suffered repeated chest infections, from which she died 4 months after admission. This case raised several clinical, ethical and legal issues and generated a spectrum of opinion as to the appropriateness of operative intervention, transfusion and provision of intensive care. We suggest that professional guidelines and the new Mental Capacity Act 2005 do not provide explicit and comprehensive guidance for practitioners. Further deliberation is required to bring about convergence between the law, ethical principles and professional guidelines.

A Classical Live Attenuated Vaccine for Sheep Pox

A classical live attenuated sheep pox vaccine was prepared using the Ranipet strain of sheep pox virus (SPV) at the 50th passage in a secondary lamb testicular cell system. The TCID50 and RD50 were 10(9.63)/ml and 10(9.51)/ml. respectively. The SID50 of SPV challenge virus was 10(5)/ml. The vaccine was found to have no adverse effects in laboratory animals, and was safe and effective in SPV seronegative lambs. In the field, 660 sheep were vaccinated with an immunizing dose containing 1 x 10(2) TCID50. Randomly selected vaccinated sheep mounted good cell-mediated immunity and humoral responses as measured by glucose utilization test and serum neutralization test, respectively, for the study period of 6 months.

Death effector domain-containing proteins DEDD and FLAME-3 form nuclear complexes with the TFIIIC102 subunit of human transcription factor IIIC

Death effector domain-containing proteins are involved in important cellular processes such as death-receptor induced apoptosis, NF-kappaB activation and ERK activation. Here we report the identification of a novel nuclear DED-containing protein, FLAME-3. FLAME-3 shares significant sequence (46.6% identical) and structural homology to another DED-containing protein, DEDD. FLAME-3 interacts with DEDD and c-FLIP (FLAME-1) but not with the other DED-containing proteins FADD, caspase-8 or caspase-10. FLAME-3 translocates to, and sequesters c-FLIP in the nucleus upon overexpression in human cell lines. Using the yeast two-hybrid system to identify DEDD-interacting proteins, the TFIIIC102 subunit of human transcription factor TFIIIC was identified as a DEDD- and FLAME-3-specific interacting protein. Co-expression of either DEDD or FLAME-3 with hTFIIIC102 in MCF-7 cells induces the translocation from the cytoplasm and sequestration of hTFIIIC102 in the nucleus, indicating that DEDD and FLAME-3 form strong heterocomplexes with hTFIIIC102 and might be important regulators of the activity of the hTFIIIC transcriptional complex. Consistent with this, overexpression of DEDD or FLAME-3 in 293 cells inhibited the expression of a luciferase-reporter gene under the control of the NF-kappaB promoter. Our data provide the first direct evidence for the involvement of DED-containing proteins in the regulation of components of the general transcription machinery in the nucleus.

Papillon-Lefevre syndrome: a report of two cases

Papillon-Lefevre Syndrome (PLS) is an inherited autosomal recessive disorder presenting with Palmar plantar Keratoderma and Juvenile Periodontitis leading to early loss of both the dentitions. Two cases of PLS in a family with a history of consanguineous descent are presented.

Red cell distribution width in the diagnosis of iron deficiency anemia

OBJECTIVE

1. To compare peripheral smear (PS) and Red cell distribution width (RDW) in diagnosis of Iron deficiency anemia (IDA) in various grades. 2. To study the changes in RDW and PS after therapy.

METHODS

Children in the age group of six months to five years with microcytic (MCV<80fl) anemia (Hemoglobin <11 g%) were evaluated. Those who had received blood transfusion and /or were already on iron therapy were excluded. Evaluation included clinical examination, complete blood count (CBC), RDW estimation microscopic examination of peripheral smear, measurement of serum iron and transferrin saturation. Children with IDA were treated with oral iron for 8 weeks and PS, CBC including RDW were repeated.

RESULT

Of the 100 children evaluated, 89 had IDA. 48% had mild, 42% had moderate and 10% had severe anemia. Transferrin saturation correlated with severity of anemia. Peripheral smear showed microcytosis and hypochromia in all cases with severe anemia, 61.5% and 22.5% of those with moderate and mild anemia respectively. RDW was suggestive of iron deficiency in 100%, 82.05% and 100% of patient with mild, moderate and severe anemia respectively.

CONCLUSION

In the diagnosis of mild and moderate iron deficiency anemia, RDW had a higher sensitivity than PS. Red cell morphology, Hb, PCV and RDW showed significant improvement after iron-therapy.

Menetrier's disease

An 8-year-old girl presented with persistent vomiting, pain abdomen and generalized edema. Barium studies and gastroscopy suggested hypertrophic gastropathy. Histopathological examination pointed the diagnosis towards Menetrier's Disease. There was spontaneous remission and the child required only supportive therapy.

A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis

X-linked inhibitor-of-apoptosis protein (XIAP) interacts with caspase-9 and inhibits its activity, whereas Smac (also known as DIABLO) relieves this inhibition through interaction with XIAP. Here we show that XIAP associates with the active caspase-9-Apaf-1 holoenzyme complex through binding to the amino terminus of the linker peptide on the small subunit of caspase-9, which becomes exposed after proteolytic processing of procaspase-9 at Asp315. Supporting this observation, point mutations that abrogate the proteolytic processing but not the catalytic activity of caspase-9, or deletion of the linker peptide, prevented caspase-9 association with XIAP and its concomitant inhibition. We note that the N-terminal four residues of caspase-9 linker peptide share significant homology with the N-terminal tetra-peptide in mature Smac and in the Drosophila proteins Hid/Grim/Reaper, defining a conserved class of IAP-binding motifs. Consistent with this finding, binding of the caspase-9 linker peptide and Smac to the BIR3 domain of XIAP is mutually exclusive, suggesting that Smac potentiates caspase-9 activity by disrupting the interaction of the linker peptide of caspase-9 with BIR3. Our studies reveal a mechanism in which binding to the BIR3 domain by two conserved peptides, one from Smac and the other one from caspase-9, has opposing effects on caspase activity and apoptosis.

Identification and characterization of murine caspase-14, a new member of the caspase family

We report here the identification and characterization of a new member of the mouse caspase family, named caspase-14. Northern blot analysis of mRNA from various tissues with caspase-14-specific probe showed a major transcript size of approximately 2.4 kb and variant transcripts of 2.0 kb and 1.5 kb. The major transcript is detected mainly in the liver and to a lesser extent in the brain and kidney. Caspase-14 cDNA encodes a 257-amino acid-long protein that has significant homology to other members of the caspase family. Like other caspases, caspase-14 has a conserved active site, pentapeptide QACRG. However, it lacks an NH2-terminal prodomain or a caspase recruitment domain, suggesting that it could be a downstream caspase that depends on other initiator caspases for activation. Consistent with this, procaspase-14 can be processed in vitro by the death receptor-associated caspase-8 and caspase-10 but not other caspases, and in vivo after stimulation of cells with anti-Fas agonist antibody or Tumor Necrosis Factor-Related Apoptosis Inducing Ligand. Furthermore, procaspase-14 can be cleaved by granzyme B. These observations suggest that caspase-14 may play a role in death receptor and granzyme B-induced apoptosis.

Evolution of tetrameric lectin Ricinus communis agglutinin from two variant groups of ricin toxin dimers

Seeds of Ricinus communis contain two types of lectins; the toxin ricin (approximately 60 kDa) and R. communis agglutinin (approximately 120 kDa). The toxin is a heterodimer composed of a toxic A subunit and a lectin B subunit, while R. communis agglutinin is a tetramer, constituted of two ricin-like dimers held together by non-covalent forces. The lactamyl Sepharose affinity-purified ricin consists of two major groups of variants designated ricin II and III [Hegde, R. & Podder, S. K. (1992) Eur. J. Biochem. 204, 155-164]. The purified A subunits of all the variants of ricins and R. communis agglutinin show heterogeneity in the molecular mass as shown for ricin before [Fulton, J. R., Blakey, C. D., Knowles, P. P., Uhr, J. W., Thorpe, P. E. & Vitetta, E. S. (1986) J. Biol. Chem. 261, 5314-5319]. Since the isoelectric points of the R. communis agglutinin variants fall between the isoelectric points of ricin II and III, we investigated the possibility that this lectin is made up of ricin II and III. The isoelectric points of the purified B subunits of R. communis agglutinin matched well with those of ricin II and III on urea-polyacrylamide isoelectric focussing gel. Further, two-dimensional electrophoretic analysis of the ricin constituants of R. communis agglutinin in the presence of 9 M urea, showed two protein bands, differing by nearly pH 2 in their isoelectric points, the more alkaline one corresponding to that of ricin III analyzed under the same conditions, while the other, although a higher molecular mass variant, corresponding well with ricin II in its isoelectric point. Based on these results and those obtained from adenine binding to A chains of both ricin and R. communis agglutinin, we provide a plausible evolutionary relationship between R. communis agglutinin and two groups of ricin variants; ricin II and III. The model predicts that one half of R. communis agglutinin is derived from ricin I and II, and the other half from ricin III. The results presented, contrary to the existing notion, unequivocally show that the two halves of R. communis agglutinin are not identical protein units, but differ both in surface charge and molecular mass.

Blk, a BH3-containing mouse protein that interacts with Bcl-2 and Bcl-xL, is a potent death agonist

We identified and cloned a novel murine member of the pro-apoptotic Bcl-2 family. This protein, designated Blk, is structurally and functionally related to human Bik and localized to the mitochondrial membrane. Blk contains a conserved BH3 domain and can interact with the anti-apoptotic proteins Bcl-2 and Bcl-xL. Ectopic expression of Blk in mammalian cells induces apoptosis, which can be inhibited by mutations in the BH3 domain and by overexpression of Bcl-2 or Bcl-xL but not by CrmA. The apoptotic activity of Blk is also inhibited by a dominant negative caspase-9, suggesting that Blk induces apoptosis through activation of the cytochrome c-Apaf-1-caspase-9 pathway.

The 24-kDa subunit of the bovine mitochondrial NADH:ubiquinone oxidoreductase is a G protein

Based on the results obtained from GTP overlay assay, immunoprecipitation, two dimensional electrophoresis and radiolabeled GTP binding, we provide evidence that the bona fide subunit of Complex I, the long known 24 kDa protein is a G protein. Bacterially expressed 24 kDa protein with additional N-terminal methionine and alanine residues or naturally expressed truncated isoform fail to bind GTP suggesting that secondary modification/ processed N-terminal end is necessary for GTP binding. Competitive inhibition of binding of radiolabeled GTP to electroblotted 24 kDa protein with unlabelled nucleotides showed that the protein binds GTP and GDP with high affinity in presence of Mg2+, and has decreased to very low affinity for ITP, CTP, GMP and UTP. A comparative binding of [gamma-35S]-GTP to Complex I and 24 kDa protein (electroblotted) suggests that the GTP binding in the native Complex is solely due to 24 kDa protein. Further, four fold difference in the binding affinities between native Complex I and 24 kDa protein (electroblotted) as seen by Scatchard analysis of the binding data indicates that protein undergoes structural rearrangement in Complex I bound form, that presumably triggers divalent cation dependent GTPase activity in native complex. We were unable to detect the effect of GTP/ GDP on the ubiquinone/ferricyanide reductase activity. Since the subunit is found missing in tissues affected by mitochondrial respiratory chain diseases, we presume that the subunit has regulatory role in the Complex I function in the electron transport chain.

A- and B-subunit variant distribution in the holoprotein variants of protein toxin abrin: variants of abrins I and III have constant toxic A subunits and variant lectin B subunits

The cytotoxic lectin abrin shows more than 30 variant forms (R. Hegde, T. K. Maiti, and S. K. Podder, 1991, Anal. Biochem. 194, 101-109). The lectin B subunit as cause for variance in abrins I and III was detected by a combination of one- and two-dimensional electrophoresis and Western blotting. Intriguingly, in abrin I but not in abrin III, association of a single A subunit with the variant B subunits shifts the holoprotein pI toward the alkaline side indicating that the subunit association involves neutralization of few negative charges. The B-subunit variants of abrins I and III overlap in their pI, and the A-subunit association gives the holoproteins a distinctness on isoelectric focusing gel. The results were also confirmed by analyzing the pH titration curves. These differences in the subunit association pattern between abrins I and III are in corroboration with the previously observed differences in the kinetics of protein synthesis inactivation and accessibility of the disulfide bridge to reducing agents in the presence or absence of putative receptor (R. Hegde, A. Karande, and S. K. Podder, 1993 Eur. J. Biochem. 215, 411-419). Further, the genetic origin of variance was confirmed by peptide mapping of the individual subunit variants. Considering a theoretical value of 0.1 to 0.2 pI/charge, a 15-17 charge difference could be predicted between the variants of two extreme pIs. The fact that the A subunits are not shared between the groups was taken to interpret that the protein synthesized as prepro form is processed posttranslationally and the processing takes place only after the disulfide bond formation between A and B subunits. The N-terminal 16 amino acids of A subunits of abrins I and III showed 26% dissimilarity. The A subunits of abrins I and III did not react with concanavalin A, indicating that the heterogeneity in the molecular weight is because of differential processing but not because of glycosylation.

Pseudocyst of the auricle: a new method of treatment

Pseudocyst of the auricle is a condition where spontaneous serous fluid collection is seen on the lateral surface of the pinna. The aetiology of this condition is not known. Several methods of treatment have been advocated in the past. We report 10 cases of unilateral pseudocyst who were treated with aspiration and pressure dressing by a plaster of Paris cast over the pinna for two weeks.

The crystal structure of the bacterial chaperonin GroEL at 2.8 A

The crystal structure of Escherichia coli GroEL shows a porous cylinder of 14 subunits made of two nearly 7-fold rotationally symmetrical rings stacked back-to-back with dyad symmetry. The subunits consist of three domains: a large equatorial domain that forms the foundation of the assembly at its waist and holds the rings together; a large loosely structured apical domain that forms the ends of the cylinder; and a small slender intermediate domain that connects the two, creating side windows. The three-dimensional structure places most of the mutationally defined functional sites on the channel walls and its outward invaginations, and at the ends of the cylinder.

Site-specific mutagenesis of the metal binding sites of porcine fructose-1,6-bisphosphatase

Mutations in the metal binding sites of porcine fructose-1,6-bisphosphatase were carried out by site-specific mutagenesis based on the crystal structure of the enzyme. The mutant and wild-type enzymes have been characterized by circular dichroism spectrometry and initial-rate kinetics. One of the mutant forms of fructose-1,6-bisphosphatase (Glu280Gln) is associated with a single metal site, whereas two other mutants (Glu97Gln and Asp118Asn) ligate two metal ions. The mutant enzymes exhibit very large decreases in kcat relative to the wild-type enzyme; however, other kinetic parameters, such as Km values, are not greatly altered. Metal binding cooperativity and binding affinity is decreased in the mutants compared to wild-type fructose-1,6-bisphosphatase. Mutations in the metal binding sites greatly enhance the enzyme's affinity for AMP, a potent regulator of fructose-1,6-bisphosphatase activity. The results of these investigations are fully consistent with predictions made on the role of specific amino acid residues at the metal binding sites in porcine fructose-1,6-bisphosphatase from X-ray diffraction studies [Zhang, Y., Liang, J.-Y., Huang, S., Ke, H., and Lipscomb, W.N. (1993) Biochemistry, 32, 1844-1857].

The variants of the protein toxins abrin and ricin. A useful guide to understanding the processing events in the toxin transport

Kinetic data on inhibition of protein synthesis in thymocyte by three abrins and ricin have been obtained. The intrinsic efficiencies of A chains of four toxins to inactivate ribosomes, as analyzed by ki-versus-concentration plots were abrin II, III > ricin > abrin I. The lag times were 90, 66, 75 and 105 min at a 0.0744 nM concentration of each of abrin I, II, III and ricin, respectively. To account for the observed differences in the dose-dependent lag time, functional and structural variables of toxins such as binding efficiency of B chains to receptors and low-pH-induced structural alterations have been analyzed. The association constants obtained by stopped flow studies showed that abrin-I (4.13 x 10(5) M-1 s-1) association with putative receptor (4-methylumbelliferyl-alpha-D-galactoside) is nearly two times more often than abrin III (2.6 x 10(5) M-1 s-1) at 20 degrees C. Equilibrium binding constants of abrin I and II to thymocyte at 37 degrees C were 2.26 x 10(7) M-1 and 2.8 x 107 M-1 respectively. pH-induced structural alterations as studied by a parallel enhancement in 8-anilino-L-naphthalene sulfonate fluorescence revealed a high degree of qualitative similarity. These results taken with a nearly identical concentration-independent lag time (minimum lag of 41-42 min) indicated that the binding efficiencies and internalization efficiencies of these toxins are the same and that the observed difference in the dose-dependent lag time is causally related to the proposed processing event. The rates of reduction of inter-subunit disulfide bond, an obligatory step in the intoxication process, have been measured and compared under a variety of conditions. Intersubunit disulfide reduction of abrin I is fourfold faster than that of abrin II at pH 7.2. The rate of disulfide reduction in abrin I could be decreased 11-fold by adding lactose, compared to that without lactose. The observed differences in the efficiencies of A chains, the dose-dependent lag period, the modulating effect of lactose on the rates of disulfide reduction and similarity in binding properties make the variants a valuable tool to probe the processing events in toxin transport in detail.

Studies on the variants of the protein toxins ricin and abrin

This study elucidates some structural and biological features of galactose-binding variants of the cytotoxic proteins ricin and abrin. An isolation procedure is reported for ricin variants from Ricinus communis seeds by using lactamyl-Sepharose affinity matrix, similar to that reported previously for variants of abrin from Abrus precatorius seeds [Hegde, R., Maiti, T. K. & Podder, S. K. (1991) Anal. Biochem. 194, 101-109]. Ricin variants, subfractionated on carboxymethyl-Sepharose CL-6B ion-exchange chromatography, were characterized further by SDS/PAGE, IEF and a binding assay. Based on the immunological cross-reactivity of antibody raised against a single variant of each of ricin and abrin, it was established that all the variants of the corresponding type are immunologically indistinguishable. Analysis of protein titration curves on an immobilized pH gradient indicated that variants of abrin I differ from other abrin variants, mainly in their acidic groups and that variance in ricin is a cause of charge substitution. Detection of subunit variants of proteins by two-dimensional gel electrophoresis showed that there are twice as many subunit variants as there are variants of holoproteins, suggesting that each variant has a set of subunit variants, which, although homologous, are not identical to the subunits of any other variant with respect to pI. Seeds obtained from polymorphic species of R. communis showed no difference in the profile of toxin variants, as analyzed by isoelectric focussing. Toxin variants obtained from red and white varieties of A. precatorius, however, showed some difference in the number of variants as well as in their relative intensities. Furthermore, variants analyzed from several single seeds of A. precatorius red type revealed a controlled distribution of lectin variants in three specific groups, indicating an involvement of at least three genes in the production of Abrus lectins. The complete absence or presence of variants in each group suggested a post-translational differential proteolytic processing, a secondary event in the production of abrin variants.

Purification and characterization of three toxins and two agglutinins from Abrus precatorius seed by using lactamyl-Sepharose affinity chromatography

Three toxins, abrin-I, -II, and -III, and two agglutinins, APA-I and -II, were purified from the seeds of Abrus precatorius by lactamyl-Sepharose affinity chromatography followed by gel filtration and DEAE-Sephacel column chromatography. Abrin-I did not bind on DEAE-Sephacel column chromatography and the bound abrin-II, abrin-III, APA-I, and APA-II were eluted with a sodium acetate gradient. The identity of each protein was established by sodium dodecylsulfate-polyacrylamide gel electrophoresis and isoelectric focusing. The relative molecular weights are abrin-I, 64,000; abrin-II and abrin-III, 63,000 each: APA-I, 130,000; and APA-II, 128,000. Isoelectric focusing revealed microheterogeneity due to the presence of isoforms in each protein. Toxicity and binding studies further confirmed the differences among the lectins. The time course of inhibition of protein synthesis in thymocytes by the toxins showed lag times of 78, 61, and 72 min with Ki's of 0.55, 0.99, and 0.74 ms-1 at a 0.63 nM concentration of each of abrin-I, -II, and -III, respectively. A Scatchard plot obtained from the equilibrium measurement for the lectins binding to lactamyl-Sepharose beads showed nonlinearity, indicating a cooperative mode of binding which was not observed for APA-I binding to Sepharose 4B beads. Further, by the criterion of the isoelectric focusing profile, it was shown that the least toxic abrin-I and the highly toxic abrin-II isolated by lactamyl-Sepharose chromatography were not retained on a low-affinity Sepharose 4B matrix, which signifies the necessity of using a high-affinity matrix for the purification of the lectins.