HLA-G gene polymorphism in human placentas: possible association of G*0106 allele with preeclampsia and miscarriage

Definite causes for several pathologies of pregnancy remain unknown. In light of several recent studies, however, diminished or aberrant HLA-G expression may be associated with certain complication of pregnancy and be linked to HLA-G polymorphism. We analyzed DNA from 60 normal placentas (controls), 140 placentas from miscarriage, 36 placentas from preeclampsia, 76 placentas from fetal hypotrophy, and 34 placentas with hypoxia for variations in coding regions (allelic groups G*0101 to G*0107) and the 14-bp deletion/insertion into the 3'-untranslated region. No statistically significant differences were observed in the distribution of allelic group between pathological placentas and controls with the exception of G*0106 allele frequency in preeclamptic compared with control placentas (21.2% and 6.6%, respectively). A greater frequency of this allele also was observed in the two subgroups of miscarriage and hypoxia compared with that in controls. In addition, presence of the 14-bp sequence was prominent in preeclampsia compared with controls (60.8% vs. 35%, respectively), and homozygotes with deletion were not detected in the pathology. The results suggest that the G*0106 allele, which is coupled with the presence of the 14-bp sequence, contributes and/or is a relevant marker in some specific complications of pregnancy, especially preeclampsia.

The human leucocyte antigen-G 14-basepair polymorphism correlates with graft-versus-host disease in unrelated bone marrow transplantation for thalassaemia

The presence of the 14-bp insertion polymorphism of the human leucocyte antigen (HLA)-G gene (HLA-G) promotes immune tolerance through increased synthesis of HLA-G molecules. We investigated this polymorphism in a large cohort of 53 thalassaemia patients transplanted from an unrelated donor. Sixteen patients (30.2%) homozygous for the 14-bp deletion had a higher risk of developing acute graft-versus-host disease (aGvHD) than patients homozygous for the 14-bp insertion (-14-bp/-14-bp vs +14-bp/+14-bp: Relative Risk = 15.0; 95% confidence interval 1.59-141.24; P = 0.008). Therefore, the 14-bp polymorphism could be an important predictive factor for aGvHD following bone marrow transplantation.

Phase II study of preoperative irradiation and chemotherapy with capecitabine in patients with locally advanced rectal carcinoma

Preoperative chemoradiotherapy has demonstrated to improve resectability and local control in locally advanced rectal cancer (LARC). 5-fluorouracil (5FU) has traditionally been the drug of choice in combination with radiation therapy. Early studies of capecitabine (CAP) have shown its potential to replace 5FU. Between March 2002 and April 2005, 31 patients with newly diagnosed LARC (T2 N+ 2 cases, T3 N0-N+ 25 cases, T4 N0-N+ 4 cases) received the combined treatment. Surgery was planned 6-8 weeks after chemoradiation. Adjuvant chemotherapy with 5FU plus leucovorin for 6 courses was given in pN+ patients. All patients completed the planned treatment. Grade 3 acute toxicity was observed in 5 patients (16%). Nineteen patients (61%) had a downstaging. A complete pathological remission was observed in 3 cases (10%). Median follow-up is of 23 months (range; 6-36 months). The results of this experience confirm the data of the literature about the feasibility and efficacy of a neoadjuvant treatment with radiation and CAP in LARC.

Partial purification and MALDI-TOF MS analysis of UN1, a tumor antigen membrane glycoprotein

UN1 is a membrane glycoprotein that is expressed in immature human thymocytes, a subpopulation of peripheral T lymphocytes, the HPB acute lymphoblastic leukemia (ALL) T-cell line and fetal thymus. We previously reported the isolation of a monoclonal antibody (UN1 mAb) recognizing the UN1 protein that was classified as "unclustered" at the 5th and 6th International Workshop and Conference on Human Leukocyte Differentiation Antigens. UN1 was highly expressed in breast cancer tissues and was undetected in non-proliferative lesions and in normal breast tissues, indicating a role for UN1 in the development of a tumorigenic phenotype of breast cancer cells. In this study, we report a partial purification of the UN1 protein from HPB-ALL T cells by anion-exchange chromatography followed by immunoprecipitation with the UN1 mAb and MALDI-TOF MS analysis. This analysis should assist in identifying the amino acid sequence of UN1.

Expression of ATP7B in normal human liver

ATP7B is a copper transporting P-type ATPase, also known as Wilson disease protein, which plays a key role in copper distribution inside cells. Recent experimental data in cell culture have shown that ATP7B putatively serves a dual function in hepatocytes: when localized to the Golgi apparatus, it has a biosynthetic role, delivering copper atoms to apoceruloplasmin; when the hepatocytes are under copper stress, ATP7B translocates to the biliary pole to transport excess copper out of the cell and into the bile canaliculus for subsequent excretion from the body via the bile. The above data on ATP7B localization have been mainly obtained in tumor cell systems in vitro. The aim of the present work was to assess the presence and localization of the Wilson disease protein in the human liver. We tested immunoreactivity for ATP7B in 10 human liver biopsies, in which no significant pathological lesion was found using a polyclonal antiserum specific for ATP7B. In the normal liver, immunoreactivity for ATP7B was observed in hepatocytes and in biliary cells. In the hepatocytes, immunoreactivity for ATP7B was observed close to the plasma membrane, both at the sinusoidal and at the biliary pole. In the biliary cells, ATP7B was localized close to the cell membrane, mainly concentrated at the basal pole of the cells. The data suggest that, in human liver, ATP7B is localized to the plasma membrane of both hepatocytes and biliary epithelial cells.

HPRTSardinia: a new point mutation causing HPRT deficiency without Lesch-Nyhan disease

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency always causing hyperuricemia presents various degrees of neurological manifestations, the most severe which is Lesch-Nyhan syndrome. The HPRT gene is situated in the region Xq26-q27.2 and consists of 9 exons. At least 300 different mutations at different sites in the HPRT coding region from exon 1 to exon 9 have been identified. A new mutation in the HPRT gene has been determined in one patient with complete deficiency of erythrocyte activity, with hyperuricemia and gout but without Lesch-Nyhan disease. Analysis of cultured fibroblasts revealed minimal residual HPRT activity mainly when guanine was the substrate. Genomic DNA sequencing demonstrated patient's mother heterozygosity for the mutation and no mutation in her brother. The mutation consists in a C-->T transversion at cDNA base 463 (C463T) in exon 6, resulting in proline to serine substitution at codon 155 (P155S). This mutation had not been reported previously and has been designated HPRT(Sardinia). The mutation identified in this patient allows some expression of functional enzyme in nucleated cells such as fibroblasts, indicating that such cell type may add further information to conventional blood analysis. A multicentre survey gathering patients with variant neurological forms could contribute to understand the pathophysiology of the neurobehavioral symptoms of HPRT deficiency.

SOD1 mutations in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS), the most common form among motoneuron diseases, is characterized by a progressive neurodegenerative process involving motor neurons in the motor cortex, brain stem and spinal cord. Sporadic (SALS) accounts for the majority of patients but in about 10% of ALS cases the disease is inherited (FALS), usually as an autosomal dominant trait. In the present study we show the results of a referred based multicenter study on the distribution of SOD1 gene mutations in the largest cohort of Italian ALS patients described so far. Two hundred and sixty-four patients (39 FALS and 225 SALS) of Italian origin were studied. In 7 out of 39 FALS patients we found the following SOD1 gene mutations: i) a new G12R missense mutation in exon 1, found in a patient with a slowly progressive disease course; ii) the G41S mutation, in four unrelated patients with rapidly progressive course complicated with cognitive decline in two of them; iii) the L114F mutation, in a patient with a slowly progressive phenotype; iv) the D90A mutation, in a heterozygous patient with atypical phenotype. In addition, in one SALS patient a previously reported synonymous variant S59S was identified. In 17 (3 FALS and 14 SALS) out of 264 patients (6.4 %) the polymorphism A-->C at position 34 of intron 3 (IVS3: + 34 A-->C) was found, and in one FALS patient a novel variant IVS3 + 62 T-->C was identified. The frequency of SOD1 gene mutations (17.9 %) in FALS cases was comparable with that found in other surveys with a similar sample size of ALS cases. No SOD1 gene mutations have been identified in SALS cases. Within FALS cases, The most frequent mutation was the G41S identified in four FALS.

Mapping of the major psoriasis-susceptibility locus (PSORS1) in a 70-Kb interval around the corneodesmosin gene (CDSN)

Numerous putative susceptibility loci have been described for psoriasis. Among the loci confirmed in the literature, PSORS1 (the major histocompatibility complex at 6p21.3) has the strongest effect. Recent studies have highlighted a 200-kb candidate region. However, this region has not been well delimited, mainly because of the strong linkage equilibrium among the associated alleles. To finely map PSORS1, we set up a study using 17 polymorphic markers in a 525-kb interval around the human leucocyte antigen C locus (HLA-C). The results uncovered five loci with alleles strongly associated with psoriasis (Sidak-corrected P [P(c)] values from 1.8 x 10(-7) to .003), all structured in a psoriasis-susceptibility haplotype (PSH). Subsequent analysis of extended haplotypes showed that the PSH was not only present on the traditional psoriasis-susceptibility extended haplotypes (HLA-Cw6-B57, HLA-Cw6-B37, and HLA-Cw6-B13) but also on a haplotype of Sardinian origin (HLA-Cw7-B58) found to be associated with psoriasis (Pc=.0009) because of an ancestral recombination with one of the susceptibility haplotypes carrying the HLA-Cw6 allele. Comparisons of the regions identical by descent among associated and nonassociated haplotypes highlighted a minimum region of 70 kb not recombinant with PSORS1, around the corneodesmosin (CDSN) gene.

A psoriasis vulgaris protective gene maps close to the HLA-C locus on the EH18.2-extended haplotype

We determined the molecular haplotypes of the HLA-A, HLA-C and HLA-B loci and the MHC class I-B-related (MIB) microsatellite in 179 unrelated psoriatic patients (72 familial cases) and in 120 controls. The HLA-A*3002-Cw*0501-B*1801-MIB1 haplotype showed a strong negative association with psoriasis vulgaris (PV) and in particular with familial PV, revealing the presence of a PV-protective gene. Analysis of association and linkage disequilibrium of the single alleles and the various two-three-four-locus segments of this haplotype indicated the presence of a protective gene telomeric to the HLA-C locus. This finding was confirmed in 13 informative multiplex PV families, in which at least one parent carried the EH18.2 haplotype. In two families, an affected sibling presented HLA-A/C recombination on the EH18.2 haplotype. A study of 12 polymorphic microsatellites in all members of the informative families, 145 PV patients, 120 controls and 32 EH18.2 homozygous healthy individuals demonstrated that the protection conferred by the EH18.2 haplotype lies within a 170 kb interval between the C143 and C244 loci, most probably in a 60 kb segment between the C132 and C244 loci.

[Neoadjuvant radiochemotherapy treatment in locally advanced rectal adenocarcinoma]

A prospective phase II study was conducted to evacuate toxicity and results of preoperative radiochemotherapy in locoregionally advanced rectal cancer (LARC). A total of 33 patients entered the study and received 45 Gy to the pelvis plus a supplemental boost of 5.4-9 Gy concurrently with 5 FU c.i. at a dose of 225-275 mg/m2. Thirty patients were operated after 5-7 weeks (20 anterior resection and 10 abdominoperineal excision). In 14 patients (47%) a downstaging was observed, 5 patients experienced a complete clearance of the primary tumor. After a median of 14 months (range, 5-27), 23 patients, are alive and well. And 8 patients experienced a disease progression (4 local-regional and 4 distant). Our results provide further evidence of the utility and effectiveness of preoperative radiochemotherapy in LARC.

Psoriasis is associated with a SNP haplotype of the corneodesmosin gene (CDSN)

A psoriasis susceptibility locus has been mapped to the HLA region in the proximity of the HLA-C locus. This critical region also contains the CDSN gene coding for the corneodesmosin protein. In a case-control association study of psoriasis in the Sardinian population, we analyzed the allele distribution of eight intragenic SNPs (positions 619, 767, 1215, 1118, 1236, 1243, 1331, 1593) of the CDSN gene and the six haplotypes that are coded by these SNPs. Our study showed that these CDSN haplotypes are very stable and well-conserved in the Sardinian population. The CDSN2 haplotype was found to be associated with susceptibility to psoriasis. The association did not depend upon any one of the intragenic SNPs taken separately. At the HLA-C locus, the Cw6 and Cw7 alleles were dragged along by linkage disequilibrium with the CDSN2 haplotype and only revealed a trend towards association with the disease. Therefore, the intragenic SNPs of the CDSN gene and the HLA-Cw6 and Cw7 alleles are not directly involved in susceptibility to psoriasis. However, the strong association of the CDSN2 haplotype suggests a possible role for the CDSN gene and its chromosome region in susceptibility to psoriasis.

Characterization of the hepatitis C virus NS2/3 processing reaction by using a purified precursor protein

The NS2-NS3 region of the hepatitis C virus polyprotein encodes a proteolytic activity that is required for processing of the NS2/3 junction. Membrane association of NS2 and the autocatalytic nature of the NS2/3 processing event have so far constituted hurdles to the detailed investigation of this reaction. We now report the first biochemical characterization of the self-processing activity of a purified NS2/3 precursor. Using multiple sequence alignments, we were able to define a minimal domain, devoid of membrane-anchoring sequences, which was still capable of performing the processing reaction. This truncated protein was efficiently expressed and processed in Escherichia coli. The processing reaction could be significantly suppressed by growth in minimal medium in the absence of added zinc ions, leading to the accumulation of an unprocessed precursor protein in inclusion bodies. This protein was purified to homogeneity, refolded, and shown to undergo processing at the authentic NS2/NS3 cleavage site with rates comparable to those observed using an in vitro-translated full-length NS2/3 precursor. Size-exclusion chromatography and a dependence of the processing rate on the concentration of truncated NS2/3 suggested a functional multimerization of the precursor protein. However, we were unable to observe trans cleavage activity between cleavage-site mutants and active-site mutants. Furthermore, the cleavage reaction of the wild-type protein was not inhibited by addition of a mutant that was unable to undergo self-processing. Site-directed mutagenesis data and the independence of the processing rate from the nature of the added metal ion argue in favor of NS2/3 being a cysteine protease having Cys993 and His952 as a catalytic dyad. We conclude that a purified protein can efficiently reproduce processing at the NS2/3 site in the absence of additional cofactors.

[Sentinel lymph nodes in breast carcinoma: why, how, when]

Thanks to a retrospective analysis of the first 250 cases of sentinel lymph nodes in breast cancer assessed by the authors over the period from October 1998 to December 2000 in the light of a careful review of the literature, it has been possible to establish the importance of careful patient selection, strict compliance with the execution technique and, above all, the need for an adequate learning curve, before the procedure is used in particular protocols and/or in routine clinical practice in the near future. In particular, the training should first of all ensure that all personnel involved, i.e. surgeons, nuclear medicine specialists, and histopathologists, should attend specific courses at qualified Institutions followed by the actual management of a certain number of consecutive cases. In order to perfect the methodology and organisation, a preliminary study in a group of patients at different stages of evolution of the disease is recommended (50 cases in the study population reported). The next phase should include a group of highly selected patients, numbering at least 50-100. The training may be considered complete when in at least 20 cases, an identification rate of at least 90% is achieved with an incidence of false negatives of not more than 5%. In the authors' experience, these results were reached after 100 selected patients, and were later consistently confirmed after a further 50 cases.

Assignment of the complete disulphide bridge pattern in the human recombinant follitropin beta-chain

The chemical assessment of the complete disulphide bridge pattern in the beta-chain of human recombinant follicotropin (betaFSH) was accomplished by integrating classical biochemical methodologies with mass spectrometric procedures. A proteolytic strategy consisting of a double digestion of native betaFSH using the broad-specificity protease subtilisin first, followed by trypsin, was employed. The resulting peptide mixture was directly analysed by FAB-MS, leading to the assignment of the first three disulphide bridges. The remaining S-S bridges were determined by HPLC fractionation of the proteolytic digest followed by ESMS analysis of the individual fractions. The pattern of cysteine couplings in betaFSH was determined as: Cys3-Cys5l, Cys17-Cys66, Cys20-Cys104, Cys28-Cys82, Cys32-Cys84 and Cys87-Cys94, confirming the arrangement inferred from the crystal structure of the homologous betaCG. A subset of the S-S bridge pattern comprising Cys3-Cys51, Cys28-Cys82 and Cys32-Cys84 constitutes a cysteine knot motif similar to that found in the growth factor superfamily.

Rat coagulating gland secretion contains a kinesin heavy chain-like protein acting as a type IV transglutaminase substrate

By a proteomic approach, we demonstrated in rat coagulating gland secretion the presence of a 120 kDa protein which shares at least 80% identity at the amino acid level with the most closely related kinesin heavy chain codified by the kinesin superfamily protein Kif5c gene. In addition, we identified 30 and 66 kDa proteolytic fragments of such a kinesin heavy chain-like protein, corresponding to the 73-299 N-terminal and 300-860 C-terminal regions, respectively. Finally, we demonstrated the occurrence in coagulating gland secretion of a 200 kDa protein probably derived by cross-linking reaction of the kinesin heavy chain-like protein with type IV transglutaminase. In fact, kinesin heavy chain-like protein and its 66 kDa proteolytic fragment were also found to act as effective acyl donor substrates for the enzyme in vitro.

Effect of deamidation on folding of ribonuclease A

The folding of ribonuclease A (RNase A) has been extensively studied by characterizing the disulfide containing intermediates using different experimental conditions and analytical techniques. So far, some aspects still remain unclear such as the role of the loop 65-72 in the folding pathway. We have studied the oxidative folding of a RNase A derivative containing at position 67 the substitution Asn --> isoAsp where the local structure of the loop 65-72 has been modified keeping intact the C65-C72 disulfide bond. By comparing the folding behavior of this mutant to that of the wild-type protein, we found that the deamidation significantly decreases the folding rate and alters the folding pathway of RNase A. Results presented here shed light on the role of the 65-72 region in the folding process of RNase A and also clarifies the effect of the deamidation on the folding/unfolding processes. On a more general ground, this study represents the first characterization of the intermediates produced along the folding of a deamidated protein.

Familial hypercholesterolemia study in Sardinia using 6 LDLR polymorphic markers based on PCR

Twenty-two Sardinian families with multiple cases of hypercholesterolemia were investigated with six polymorphic markers of the low-density lipoprotein receptor (LDLR) gene that could be quickly analyzed by PCR-based methods. Five single nucleotide polymorphisms (SNP) in exons 8, 10, 13, 15, and 18 and a microsatellite marker flanking the 3' end of the LDLR gene were used to define the haplotypes at the LDLR locus for familial hypercholesterolemia (FH) diagnosis within families. No significant differences were observed between the allele frequencies of the normal and mutant chromosomes. In two families, hypercholesterolemia did not cosegregate with the LDLR locus. In the remaining 20 FH chromosomes, seven different haplotypes were identified. The same haplotypes were found with a similar frequency among the 61 normal chromosomes. Other five haplotypes were characteristic only of normal chromosomes. These data provide no evidence for a gene founder effect in the Sardinian population and, instead, highlight a pattern of genetic heterogeneity comparable with that found in mainland European populations. The replacement of the restriction fragment length polymorphisms currently used in the genetic analysis of FH with PCR-based markers proved to be a simple and less time-consuming method and did not reduce informativity in the molecular analysis of FH families.

Structural analysis of modified forms of recombinant IFN-beta produced under stress-simulating conditions

The present study focused on the investigation of the chemical stability of recombinant human interferon-beta (rhIFN-beta) tested in vitro by chemical treatments that simulate stress-induced conditions that may occur during handling, storage or ageing of protein samples. Mild oxidation and/or alkylation of the recombinant protein showed that the four methionines occurring in the interferon displayed different chemical susceptibility in that Met36 and Met117 were fully modified, whereas Met1 showed only little modification and Met62 was completely resistant. Moreover, incubation of rhIFN-beta under alkaline conditions resulted in the formation of a covalent dimeric species stabilised by an intermolecular disulphide bridge involving the free SH group of Cys17 from each polypeptide chain. Analysis of biological activity of the different IFN-beta derivatives showed that rhIFN-beta fully retains its specific activity following mild oxidation treatments whereas reaction with a high concentration of alkylating agents or incubation under alkaline conditions strongly reduce its specific antiviral activity.

Association of monoamine oxidase B alleles with age at onset in amyotrophic lateral sclerosis

An active role of monoamine oxidase B (MAO-B) in the pathogenesis of neurodegenerative disorders such as Parkinson's disease has been proposed as the enzyme is known to be a generator of free radicals which seem to be responsible for neuron oxidative damage. We evaluated the influence of MAO-B in the pathogenesis of the sporadic forms of Amyotrophic lateral sclerosis (ALS) by studying the MAO-B allele distribution in 51 patients and 71 healthy controls. MAO-B did not directly result in a risk factor for ALS but seemed to strongly influence age at onset. The mean ALS onset age was significantly higher in individuals carrying allele 5 compared to individuals without this allele (60.4 +/- 8.1 vs. 52.1 +/- 10.3 years; P = 0.004). These results, in agreement with findings in the literature, suggest an increased MAO-B expression in ALS and support the hypothesis that neuronal cell death in neurodegenerative diseases is triggered by astroglial reaction.

Conformational changes in human hepatitis C virus NS3 protease upon binding of product-based inhibitors

One of the most promising approaches to anti-hepatitis C virus drug discovery is the development of inhibitors of the virally encoded protease NS3. This chymotrypsin-like serine protease is essential for the maturation of the viral polyprotein, and processing requires complex formation between NS3 and its cofactor NS4A. Recently, we reported on the discovery of potent cleavage product-derived inhibitors [Ingallinella et al. (1998) Biochemistry 37, 8906-8914]. Here we study the interaction of these inhibitors with NS3 and the NS3/cofactor complex. Inhibitors bind NS3 according to an induced-fit mechanism. In the absence of cofactor different binding modes are apparent, while in the presence of cofactor all inhibitors show the same binding mode with a small rearrangement in the NS3 structure, as suggested by circular dichroism spectroscopy. These data are consistent with the hypothesis that NS4A complexation induces an NS3 structure that is already (but not entirely) preorganized for substrate binding not only for what concerns the S' site, as already suggested, but also for the S site. Inhibitor binding to the NS3/cofactor complex induces the stabilization of the enzyme structure as highlighted by limited proteolysis experiments. We envisage that this may occur through stabilization of the individual N-terminal and C-terminal domains where the cofactor and inhibitor, respectively, bind and subsequent tightening of the interdomain interaction in the ternary complex.

Conformational changes in the NS3 protease from hepatitis C virus strain Bk monitored by limited proteolysis and mass spectrometry

Conformational changes occurring within the NS3 protease domain from the hepatitis C virus Bk strain (NS3(1-180)) under different physico-chemical conditions either in the absence or in the presence of its cofactor Pep4A were investigated by limited proteolysis experiments. Because the surface accessibility of the protein is affected by conformational changes, when comparative experiments were carried out on NS3(1-180) either at different glycerol concentrations or in the presence of Pep4A, differential peptide maps were obtained from which protein regions involved in the structural changes could be inferred. The surface topology of isolated NS3(1-180) in solution was essentially consistent with the crystal structure of the protein with the N-terminal segment showing a high conformational flexibility. At higher glycerol concentration, the protease assumed a more compact structure showing a decrease in the accessibility of the N-terminal segment that either was forced to interact with the protein or originate intermolecular interactions with neighboring molecules. Binding of the cofactor Pep4A caused the displacement of the N-terminal arm from the protein moiety, leading this segment to again adopt an open and flexible conformation, thus suggesting that the N-terminus of the protease contributes only marginally to the stability of the complex. The observed conformational changes might be directly correlated with the activation mechanism of the protease by either the cosolvent or the cofactor peptide because they lead to tighter packing of the substrate binding site.

HLA-B35 frequency variations correlate with malaria infection in Sardinia

The hypothesis of a possible selective role of malaria in HLA allele frequency variations was investigated in Sardinia by typing completely 1,039 individuals for HLA: 536 from six lowland villages exposed to malaria until 1948, and 503 from six highland villages with no history of malaria. Another 1,928 individuals from 136 villages scattered all over the island were studied to establish if the HLA allele frequencies among villages correlated with the malaria incidence and/or altitude above sea level. Only the HLA-B35 allele yielded significantly higher frequencies in the lowland versus the highland villages (P<1 x 10(-5)). The observed B35 variance was 9.5 times higher than expected in the absence of selection, showing an adaptive origin. The highly significant positive correlation found between HLA-B35 frequency and malaria in 136 villages suggests that malaria has been the selective factor for HLA-B35 in Sardinia.

Topology of the calmodulin-melittin complex

The topology of the Ca2+-calmodulin-melittin ternary complex has been investigated by a combined strategy which integrates limited proteolysis and cross-linking experiments with mass spectrometric methodologies. The rationale behind the methods is that the interface regions of two interacting proteins are accessible to the solvent in the isolated molecules, whereas they become protected following the formation of the complex. Therefore, when limited proteolysis experiments are carried out on both the isolated proteins and the complex, differential peptide maps are obtained from which the interface regions can be inferred. Alternatively, cross-linking reactions performed under strictly controlled conditions lead to the identification of spatially closed amino acid residues in the complex. Mass spectrometry can be employed in both procedures for the definition of the cleavage sites and to identify covalently linked residues. Our results show that melittin interacts with calmodulin by adopting a parallel orientation, i.e. the N and C-terminal halves of the peptide are anchored to the amino and carboxy-terminal domains of the protein, respectively. This orientation is inverted with respect to all the peptide substrates examined so far. A model of the complex was designed and refined on the basis of the experimental results, supporting the above conclusions. This finding reveals a further dimension to the already remarkable capability of calmodulin in binding different protein substrates, providing this protein with the capability of regulating an even larger number of enzymes.

Amino acid sequence, S-S bridge arrangement and distribution in plant tissues of thionins from Viscum album

The complete primary structure of a cytotoxic 5 kDa polypeptide, viscotoxin A1, isolated from Viscum album L., has been determined by combining classical Edman degradation methodology with advanced mass spectrometric procedures. The same integrated approach allowed correction of the sequence of viscotoxin A2 and definition of the pattern of the disulfide bridges. The arrangement of the cysteine pairing was determined as Cys3-Cys40, Cys4-Cys32 and Cys16-Cys26. The primary structure of viscotoxin A1 shares a high degree of similarity with the known viscotoxins and more generally with the plant alpha- and beta-thionins. The pattern of S-S bridges determined for viscotoxin A2 and A1 is similar to that inferred by X-ray and NMR analysis in crambin and related to that present in alpha-purothionin and beta-hordothionin, thus indicating a highly conserved organization of the S-S pairings within the entire family. This arrangement of S-S bridges describes a peculiar structural motif, indicated as 'concentric motif', which is suggested to stabilize a common structure occurring in various small proteins able to interact with cell membranes. The distribution of the new variant toxin in different mistletoe subspecies was investigated. Viscotoxin A1 is abundant in the seeds of the three European subspecies of V. album whereas it represents a minor component in the shoots.