Platelet type III collagen binding protein (TIIICBP) presents high biochemical and functional similarities with kindlin-3

Type III collagen binding protein (TIIICBP) was previously described as a platelet membrane protein that recognizes the KOGEOGPK peptide sequence within type III collagen. In order to better characterize this protein, we performed different approaches including mass spectrometry sequencing and functional experiments. This study leads to identify high biochemical and functional similarities between TIIICBP and kindlin-3, a member of a family of focal adhesion proteins. Indeed, mass spectrometry surveys indicated that TIIICBP contains several peptides identical to kindlin-3, covering 41% of the amino acid sequence. Polyclonal antibodies raised against a kindlin-3 specific N-terminal sequence, recognized and immunoprecipitated TIIICBP from platelet lysates. Electron microscopy and flow cytometry experiments showed that kindlin-3, as well as TIIICBP, were present associated to platelet membrane and a translocation of cytosolic kindlin-3 to the platelet membrane was observed after platelet activation. Similarly to anti-TIIICBP antibodies and the KOGEOGPK peptide, anti-kindlin-3 antibodies inhibited platelet interactions with type III collagen under flow conditions and slowed down platelet aggregation induced by glycoprotein VI agonists; e.g. collagen-related peptides and convulxin. In addition, the anti-kindlin-3 antibody inhibited platelet aggregation induced by low - but not high - doses of ADP or thrombin which depends on α(IIb)β(3) integrin function. In conclusion, our results show that the peptides identified by mass spectrometry from purified TIIICBP correspond to the kindlin-3 protein and demonstrate biochemical and functional similarities between TIIICBP and kindlin-3, strengthening a key role for TIIICBP/kindlin-3 in platelet interactions with collagen by cooperating with glycoprotein VI activation and integrin clustering in focal adhesion complexes.

Differential RNA-binding activity of the hnRNP G protein correlated with the sex genotype in the amphibian oocyte

A proteomic approach has enabled the identification of an orthologue of the splicing factor hnRNP G in the amphibians Xenopus tropicalis, Ambystoma mexicanum, Notophthalmus viridescens and Pleurodeles walt, which shows a specific RNA-binding affinity similar to that of the human hnRN G protein. Three isoforms of this protein with a differential binding affinity for a specific RNA probe were identified in the P. walt oocyte. In situ hybridization to lampbrush chromosomes of P. waltl revealed the presence of a family of hnRNP G genes, which were mapped on the Z and W chromosomes and one autosome. This indicates that the isoforms identified in this study are possibly encoded by a gene family linked to the evolution of sex chromosomes similarly to the hnRNP G/RBMX gene family in mammals.

Dansyl-peptides matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) and tandem mass spectrometric (MS/MS) features improve the liquid chromatography/MALDI-MS/MS analysis of the proteome

Peptide tagging is a useful tool to improve matrix-assisted laser desorption/ionization tandem mass spectrometric (MALDI-MS/MS) analysis. We present a new application of the use of the dansyl chloride (DNS-Cl). DNS-Cl is a specific primary amine reagent widely used in protein biochemistry. It adds a fluorescent dimethylaminonaphthalene moiety to the molecule. The evaluation of MALDI-MS and MS/MS analyses of dansylated peptides shows that dansylation raises the ionization efficiency of the most hydrophilic species compared with the most hydrophobic ones. Consequently, higher Mascot scores and protein sequence coverage are obtained by combining MS and MS/MS data of native and tagged samples. The N-terminal DNS-Cl sulfonation improves the peptide fragmentation and promotes the generation of b-fragments allowing better peptide sequencing. In addition, we set up a labeling protocol based on the microwave chemistry. Peptide dansylation proved to be a rapid and cheap method to improve the performance of liquid chromatography (LC)/MALDI-MS/MS analysis at the proteomic scale in terms of peptide detection and sequence coverage.

Highly cytotoxic and neurotoxic acetogenins of the Annonaceae: new putative biological targets of squamocin detected by activity-based protein profiling

Acetogenins of the Annonaceae are strong inhibitors of mitochondrial complex I but discrepancies in the structure/activity relationships pled the search for other targets within the whole cell proteome. Combining hemisynthetic work, Cu-catalyzed Huisgen cycloaddition and proteomic techniques we have identified new putative protein targets of squamocin ruling out the previously accepted 'complex I dogma'. These results give new insights into the mechanism of action of these potent neurotoxic molecules.

Regulatory function of the P295-T311 motif of the estrogen receptor alpha - does proteasomal degradation of the receptor induce emergence of peptides implicated in estrogenic responses?

The way in which estrogen receptor α (ERα) mediates gene transcription and hormone-dependent cancer cell proliferation is now being largely reconsidered in view of several recent discoveries. ERα-mediated transcription appears to be a cyclic and transient process where the proteasome - and thus receptor degradation - plays a pivotal role. In view of our recent investigations, which demonstrate the estrogenic activity of a synthetic peptide corresponding to a regulatory motif of the receptor (ERα17p), we propose that ERα proteasomal degradation could induce the emergence of regulatory peptide(s). The latter would function as a signal and contribute to the ERα activation process, amplifying the initial hormonal stimulation and giving rise to sustained estrogenic response.

Trophic effect in MCF-7 cells of ERalpha17p, a peptide corresponding to a platform regulatory motif of the estrogen receptor alpha--underlying mechanisms

As yet, estrogen receptor alpha (ERalpha) inhibitors used in clinical practice target a unique site, i.e. the hormone-binding pocket. With the aim of discovering other potential therapeutic targets in the receptor, we studied its AF-2a domain, a site that proves to be critical for ligand-independent ERalpha activity. Previous studies from our laboratory highlighted an auto-inhibitory action associated with a site included in this domain, i.e. the P295-T311 sequence. Accordingly, a deletion of this sequence produces a constitutively activated receptor mutant. More interestingly, a synthetic peptide with the P295-T311 sequence (ERalpha17p) elicits in breast cancer cell lines estrogenic responses that may be ascribed to a competitive mechanism towards the P295-T311-associated auto-inhibition of ERalpha. In the present study, we show that ERalpha17p sustains MCF-7 cell growth in estrogen-depleted culture medium by inducing molecular events promoting G1/S phase transition. We demonstrate, moreover, that this proliferative activity is associated with receptor down regulation (acceleration of ERalpha degradation and repression of ESR1 gene transcription), similar to that induced by estrogen agonists. Complementary studies suggest that our observations may be, at least in part, relevant to a competitive inhibition affecting ERalpha-Hsp70 association. Hence, the design of drugs able to stabilize ERalpha-Hsp70 complexes - where the receptor is in an inactive conformation - may be of therapeutic value.

A proteomic kinetic analysis of IGROV1 ovarian carcinoma cell line response to cisplatin treatment

Ovarian cancer is one of the leading causes of mortality by gynecological cancer. Despite good response to surgery and initial chemotherapy, essentially based on cisplatin (cis-diamino-dichloro-platinum(II) (CDDP)) compounds, frequent recurrences with chemoresistance acquisition are responsible for poor prognosis. Several mechanisms have been described as implicated in CDDP resistance, however they are not sufficient to exhaustively account for this resistance emergence. We applied a proteomic approach based on 2-DE coupled with MS (MALDI-TOF/TOF) to identify proteins associated with chemoresistance induced by CDDP. A kinetic analysis of IGROV1 cell behavior following treatment with CDDP and subsequent statistical analysis revealed time and/or concentration-dependent modifications in protein expression. We evidenced events such as decreased amino-acid and nucleotide synthesis potentially associated with cell cycle blockade, and variations that may be related to resistance acquisition, such as possible enhanced glycolysis and increased proliferating potential. Moreover, overexpressions of aldehyde dehydrogenase 1 and both cytokeratins 8 and 18 were consistent with our previous findings, demonstrating that expression of these proteins was increased in cisplatin-resistant IGROV1-R10 as compared to IGROV1 parental cells. Identification of such proteins could allow improved understanding of the mechanisms leading to cell death or survival and, thus, to the acquisition of chemoresistance.

Nitration of a critical tyrosine residue in the allosteric inhibitor site of muscle glycogen phosphorylase impairs its catalytic activity

Muscle glycogen phosphorylase (GP) is a key enzyme in glucose metabolism, and its impairment can lead to muscle dysfunction. Tyrosine nitration of glycogen phosphorylase occurs during aging and has been suggested to be involved in progressive loss of muscle performance. Here, we show that GP (in its T and R form) is irreversibly impaired by exposure to peroxynitrite, a biological nitrogen species known to nitrate reactive tyrosine residues, and to be involved in physiological and pathological processes. Kinetic and biochemical analysis indicated that irreversible inactivation of GP by peroxynitrite is due to the fast (k(inact)=3 x 10(4) M(-1) s(-1)) nitration of a unique tyrosine residue of the enzyme. Endogenous GP was tyrosine nitrated and irreversibly inactivated in skeletal muscle cells upon exposure to peroxynitrite, with concomitant impairment of glycogen mobilization. Ligand protection assays and mass spectrometry analysis using purified GP suggested that the peroxynitrite-dependent inactivation of the enzyme could be due to the nitration of Tyr613, a key amino acid of the allosteric inhibitor site of the enzyme. Our findings suggest that GP functions may be regulated by tyrosine nitration.

Methylation of aquaporins in plant plasma membrane

A thorough analysis, using MS, of aquaporins expressed in plant root PM (plasma membrane) was performed, with the objective of revealing novel post-translational regulations. Here we show that the N-terminal tail of PIP (PM intrinsic protein) aquaporins can exhibit multiple modifications and is differentially processed between members of the PIP1 and PIP2 subclasses. Thus the initiating methionine was acetylated or cleaved in native PIP1 and PIP2 isoforms respectively. In addition, several residues were detected to be methylated in PIP2 aquaporins. Lys3 and Glu6 of PIP2;1, one of the most abundant aquaporins in the PM, occurred as di- and mono-methylated residues respectively. Ectopic expression in Arabidopsis suspension cells of PIP2;1, either wild-type or with altered methylation sites, revealed an interplay between methylation at the two sites. Measurements of water transport in PM vesicles purified from these cells suggested that PIP2;1 methylation does not interfere with the aquaporin intrinsic water permeability. In conclusion, the present study identifies methylation as a novel post-translational modification of aquaporins, and even plant membrane proteins, and may represent a critical advance towards the identification of new regulatory mechanisms of membrane transport.

AKAP150, a switch to convert mechano-, pH- and arachidonic acid-sensitive TREK K(+) channels into open leak channels

TREK channels are unique among two-pore-domain K(+) channels. They are activated by polyunsaturated fatty acids (PUFAs) including arachidonic acid (AA), phospholipids, mechanical stretch and intracellular acidification. They are inhibited by neurotransmitters and hormones. TREK-1 knockout mice have impaired PUFA-mediated neuroprotection to ischemia, reduced sensitivity to volatile anesthetics and altered perception of pain. Here, we show that the A-kinase-anchoring protein AKAP150 is a constituent of native TREK-1 channels. Its binding to a key regulatory domain of TREK-1 transforms low-activity outwardly rectifying currents into robust leak conductances insensitive to AA, stretch and acidification. Inhibition of the TREK-1/AKAP150 complex by Gs-coupled receptors such as serotonin 5HT4sR and noradrenaline beta2AR is as extensive as for TREK-1 alone, but is faster. Inhibition of TREK-1/AKAP150 by Gq-coupled receptors such as serotonin 5HT2bR and glutamate mGluR5 is much reduced when compared to TREK-1 alone. The association of AKAP150 with TREK channels integrates them into a postsynaptic scaffold where both G-protein-coupled membrane receptors (as demonstrated here for beta2AR) and TREK-1 dock simultaneously.

Comparative proteomic analysis of extracellular matrix proteins secreted by two types of skin fibroblasts

The hair follicle dermal papilla is composed primarily of extracellular matrix (ECM) proteins secreted by resident fibroblasts. Dermal papilla is endowed with hair morphogenic properties, yet its composition is poorly characterized. In an attempt to understand its specificity better, we compared the protein composition of ECM secreted by cultured dermal papilla fibroblasts with that of dermal fibroblasts. ECM proteins are generally large, difficult to solubilize, and abundantly post-translationally modified. We thus implemented an original protocol for analyzing them: ECM samples were enzymatically digested directly in the culture flasks and analyzed by LC-MS/MS. Sequencing of proteolytic peptides by MS/MS yielded protein identification. The relative abundance of a given protein in dermal fibroblast versus dermal papilla samples was estimated by comparing proteolytic peptide intensities detected by MS. Using this approach, several matrix proteins were found to be present at markedly different levels in each ECM type; in particular, thrombospondin 1 and fibronectin appeared to be overrepresented in the dermal papilla fibroblast ECM. MS results were supported by Western blot and immunostaining experiments. In addition, peptide intensities were processed in two ways, which proved to favor either the quantification accuracy or the information precision at the sequence level.

Polycalin (chlorophyllid A binding protein): a novel, very large fluorescent lipocalin from the midgut of the domestic silkworm Bombyx mori L

We studied a protein from the midgut of the silkworm Bombyx mori characterized by its ability to bind the prosthetic group of chlorophyll, that confers fluorescent properties to this protein. Several techniques, 2D electrophoresis purification, MS-MS and Maldi-TOF peptide sequencing, RT-PCR and nucleotide sequencing were used to obtain the nucleotide sequence and the deduced amino acid sequence. The coding sequence was compared to the gene sequence to define the number and size of introns and exons. The gene spanned 45.5 kb of DNA and consisted of 46 exons. The cDNA encoded a protein of 2721 amino acids. The protein was identified as a lipocalin with novel features. Most lipocalins are proteins with high affinity to small lipophilic molecules, with a molecular size in the 25 kDa range and a well conserved tertiary structure. The apoprotein described here revealed 15 lipocalin like structures, in line. We called this protein a polycalin (pentadecacalin).

Crustacean hyperglycemic and vitellogenesis-inhibiting hormones in the lobster Homarus gammarus

Crustacean hyperglycemic hormone (CHH) and vitellogenesis-inhibiting hormone (VIH), produced by the X organ-sinus gland neurosecretory complex, belong to a peptide group referred to as the CHH family, which is widely distributed in arthropods. In this study, genetic variants and post-translationally modified isoforms of CHH and VIH were characterized in the European lobster Homarus gammarus. With the use of RP-HPLC and ELISA with specific antibodies that discriminate between stereoisomers of CHH and VIH, two groups of CHH-immunoreactive peaks were characterized from HPLC fractions of sinus gland extract (CHH A and CHH B); each group contained two variants (CHH and D-Phe3CHH). In the same way, two VIH-immunoreactive peaks (VIH and D-Trp4VIH) were demonstrated in HPLC fractions from sinus gland extract. The masses of these different neuropeptides were determined by FT-ICR MS: CHH A and CHH B spectra exhibited monoisotopic ions at 8557.05 Da and 8527.04 Da, respectively, and both VIH isomers displayed an m/z value of 9129.19 Da. Two full-length cDNAs encoding preprohomones of CHH A and CHH B and only one cDNA for VIH precursor were cloned and sequenced from X organ RNA. Comparison of CHH sequences between European lobster and other Astacoidea suggests that the most hydrophobic form appeared first during crustacean evolution.

Phosphorylation of viral RNA-dependent RNA polymerase and its role in replication of a plus-strand RNA virus

Central to the process of plus-strand RNA virus genome amplification is the viral RNA-dependent RNA polymerase (RdRp). Understanding its regulation is of great importance given its essential function in viral replication and the common architecture and catalytic mechanism of polymerases. Here we show that Turnip yellow mosaic virus (TYMV) RdRp is phosphorylated, when expressed both individually and in the context of viral infection. Using a comprehensive biochemical approach, including metabolic labeling and mass spectrometry analyses, phosphorylation sites were mapped within an N-terminal PEST sequence and within the highly conserved palm subdomain of RNA polymerases. Systematic mutational analysis of the corresponding residues in a reverse genetic system demonstrated their importance for TYMV infectivity. Upon mutation of the phosphorylation sites, distinct steps of the viral cycle appeared affected, but in contrast to other plus-strand RNA viruses, the interaction between viral replication proteins was unaltered. Our results also highlighted the role of another TYMV-encoded replication protein as an antagonistic protein that may prevent the inhibitory effect of RdRp phosphorylation on viral infectivity. Based on these data, we propose that phosphorylation-dependent regulatory mechanisms are essential for viral RdRp function and virus replication.

Fourier transform mass spectrometry: A powerful tool for toxin analysis

The crude venom of Conus virgo was analyzed by Fourier transform mass spectrometry (FTMS) using both nano-electrospray ionization and MALDI. The analyses were performed directly on the crude venom, without chromatographic separation. The mass fingerprinting of the venom yielded 64 distinct molecular masses in the range 500-4500 Da with two major components at 1328.5142 and 1358.5592 Da. To facilitate the de novo sequencing of these compounds, the disulfide bonds of all components were reduced for the whole venom. The mass accuracy, resolution and sensitivity provided by FTMS were necessary to complete the sequencing of the two new peptides named ViVA and ViVB, that turned out to be conotoxins belonging to the T-superfamily, with the disulfide framework V. The peptides shared 80% similarity and as often observed for this class of compound, they were highly post-translationally modified: amidated C-terminus, pyroglutamic acid residue at the N-terminus and two disulfide bonds. Complementary online nano-LC-nano-ESI-FTMS experiments were undertaken. Among the 130 molecular masses found in the coupling experiments, only 45 were common with those obtained in the direct approach, which means that 21 compounds observed by nano-ESI-FTMS were not detected. This clearly shows that some discriminations against some classes of compounds occur when a chromatographic step is used before mass spectrometry.

Analysis of the dynamicBacillus subtilis Ser/Thr/Tyr phosphoproteome implicated in a wide variety of cellular processes

The physiological role of proteins phosphorylated on serine/threonine/tyrosine (Ser/Thr/Tyr) residues or the identity of the corresponding kinases and phosphatases is generally poorly understood in bacteria. As a first step in analysing the importance of such phosphorylation, we sought to establish the nature of the Ser/Thr/Tyr phosphoproteome in Bacillus subtilis, using in vivo labelling with [(32)P]-orthophosphate, one-unit pH 2-DE, combined with MS. Highly reproducible 2-D profiles of phosphoproteins were obtained with early stationary-phase cells. The 2-D profiles contained at least 80 clearly labelled spots in the pH range 4-7. Forty-six spots were analysed by MS (confirmed in most cases by LC-MS/MS), identifying a total of 29 different proteins, with 19 identified for the first time as bacterial phosphoproteins. These phosphoproteins are implicated in a wide variety of cellular processes, including carbon and energy metabolism, transport, stress and development. Significant changes to the profiles were obtained as a result of cold, heat or osmotic shock, demonstrating that, in stationary-phase cells, the phosphoproteome is dynamic. An initial comparative study indicated that at least 25 [(32)P]-labelled spots were also stained by Pro-Q Diamond, with apparently six additional phosphoproteins uniquely detected by Pro-Q.

Inactivation of the proteasome by 4-hydroxy-2-nonenal is site specific and dependant on 20S proteasome subtypes

The proteasome represents a major intracellular proteolytic system responsible for the degradation of oxidized and ubiquitinated proteins in both the nucleus and cytoplasm. We have previously reported that proteasome undergoes modification by the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) and exhibits declines in peptidase activities during cardiac ischemia/reperfusion. This study was undertaken to characterize the effects of HNE on the structure and function of the 20S proteasome. To assess potential tissue-specific differences in the response to HNE, we utilized purified 20S proteasome from heart and liver, tissues that express different proteasome subtypes. Following incubation of heart and liver 20S proteasome with HNE, changes in the 2D gel electrophoresis patterns and peptidase activities of the proteasome were evaluated. Proteasome subunits were identified by mass spectrometry prior to and following treatment with HNE. Our results demonstrate that specific subunits of the 20S proteasome are targeted for modification by HNE and that modified proteasome exhibits selective alterations in peptidase activities. The results provide evidence for a likely mechanism of proteasome inactivation in response to oxidative stress particularly during cardiac ischemia/reperfusion.

Proteomics of human umbilical vein endothelial cells applied to etoposide-induced apoptosis

We have undertaken to continue the proteomic study of human umbilical vein endothelial cells (HUVECs) using the combination of 2-DE, automated trypsin digestion, and PMF analysis after MALDI-TOF MS and peptide sequencing using nano LC-ESI-MS/MS. The overall functional characterization of the 162 identified proteins from primary cultures of HUVECs confirms the metabolic capabilities of endothelium and illustrates various cellular functions more related to cell motility and angiogenesis, protein folding, anti-oxidant defenses, signal transduction, proteasome pathway and resistance to apoptosis. In comparison with controls cells, the differential proteomic analysis of HUVECs treated by the pro-apoptotic topoisomerase inhibitor etoposide further revealed the variation of eight proteins, namely, GRP78, GRP94, valosin-containing protein, proteinase inhibitor 9, cofilin, 37-kDa laminin receptor protein, bovine apolipoprotein, and tropomyosin. These data suggest that etoposide-induced apoptosis of human vascular endothelial cells results from the intricate involvement of multiple apoptosis processes including at least the mitochondrial and the ER stress pathways. The presented 2-D pattern and protein database, as well as the data related to apoptosis of HUVECs, are available at http://www.huvec.com.

Apport de l’analyse protéomique associant électrophorèse bi-dimensionnelle et spectrométrie de masse en lacrymologie

PURPOSE

Identification of a lacrimal protein by proteomic analysis, i.e., two-dimensional electrophoresis and mass spectrometry.

MATERIAL AND METHODS

We studied the tears of a 25-year-old female with adrenal gland hyperplasia and hyperandrogenism complaining of chronic dryness and mild bilateral papillary hypertrophy. An allergologic workup was negative. Agarose electrophoresis of the tears showed a bilateral high level of rapid migrated proteins.

RESULTS

Dodecyl sulfate polyacrylamide gel electrophoresis of the tears from both eyes showed a highly stained 15-kDa band after Coomassie colloidal blue coloration compared to controls. On two-dimensional electrophoresis, this band focused on a single spot at pI 7.0. After tryptic digestion in gel, peptide mass fingerprint analysis by matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry provided clear identification of cystatin SN. It is known that mRNA regulated by androgens and encoding glycoproteins homologous to human cystatin exists in the rat lacrimal gland.

CONCLUSION

We conclude that the hyperandrogenism of the patient may be cause for the hypersecretion of this cystatin SN, giving an explanation for the high level of rapid migrated proteins (lipocalins). This result provides a concrete example of the proteomic tool used to identify lacrimal proteins, still largely unknown.

Heterogeneous nuclear ribonucleoprotein A2/B1 identified as an autoantigen in autoimmune hepatitis by proteome analysis

Our aim was to characterize antinuclear antibody (ANA) targets in type 1 autoimmune hepatitis (AIH1) using a proteomic tool. ANA-positive sera from 29 patients with AIH1 and 14 negative controls were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. The principal antigens identified were a 30 kDa triplet band which was recognized by 79% of patient sera and 14% of control sera, and a 36 kDa antigen which was recognized by 52% and 14% of sera, respectively. The latter antigen was studied in more detail using two-dimensional electrophoresis (2-DE) and mass spectrometry (MS). Its identification corresponded to heterogeneous nuclear ribonucleoprotein A2/B1. This paper presents the first description of this protein as an antigen in AIH1.

Cellular prion protein/laminin receptor: distribution in adult central nervous system and characterization of an isoform associated with a subtype of cortical neurons

The 67-kDa LR protein was originally discovered as a non-integrin laminin receptor. Several more recent in vitro studies demonstrated the function of 67-kDa LR and its related 'precursor' form 37-kDa LRP as receptors of cellular prion protein and their implication in abnormal prion protein propagation in vitro. In addition, expression of both proteins was shown to increase considerably in the brain of scrapie-infected mice and hamsters. While LRP/LR are thus likely to play important roles in neuronal cell adhesion, survival and homeostasis and during pathological disorders, little is known so far about their fine cellular distribution in adult central nervous system. Using immunocytochemistry and western blotting, we show here that the 67-kDa LR is the major receptor form in adult rat brain and spinal cord, expressed within the cytoplasm and at the plasma membrane of most neurons and in a subset of glial cells. The overall distribution of LR correlates well with that reported for laminin-1 but also with brain regions classically associated with prion-related neurodegeneration. In contrast to LR, the 37-kDa LRP form is much less abundant in adult than in postnatal central nervous system. Characterization of a novel antibody allowed us to study the distribution across tissues of cell membrane-associated LRP. Interestingly, this form is almost exclusively found on a subclass of parvalbumin-immunoreactive cortical interneurons known to degenerate during the early stages of Creutzfeldt-Jakob disease. Our demonstration of local differences in the expression of particular LRP/LR isoforms may be a first step towards unraveling their specific molecular interactions.

Fe2+ -catalyzed oxidative cleavages of Ca2+ -ATPase reveal novel features of its pumping mechanism

We have analyzed the Fe2+ -catalyzed oxidative cleavages of Ca2+ -ATPase in the presence of Ca2+, with or without the ATP analog 5'-adenylyl-beta,gamma-imidodiphosphate (AMP-PNP) or in the presence of the inhibitor thapsigargin. To identify the positions of cleavages as precisely as possible, we have used previously identified proteinase K and tryptic fragments as a standard, advanced mass spectrometry techniques, as well as specific antibodies. A number of cleavages are similar to those described for Na+,K+ -ATPase or other P-type pumps and are expected on the basis of the putative Mg2+ binding residues near the phosphorylated Asp351 in E1 or E2P conformations. However, intriguing new features have also been observed. These include a Fe2+ site near M3, which cannot be due to the presence of histidine residues as it was postulated in the case of Na+,K+ -ATPase and H+,K+ -ATPase. This site could represent a Ca2+ binding zone between M1 and M3, preceding Ca2+ occlusion within M4, 5, 6, and 8. In addition, we present evidence that, in the non-crystalline state, the N- and P-domain may approach each other, at least temporarily, in the presence of Ca2+ (E1Ca2 conformation), whereas the presence of Mg.ATP stabilizes the N to P interaction (E1.Mg.ATP conformation).