Polyglutamylated .alpha.-tubulin can enter the tyrosination/detyrosination cycle

We have previously identified a major modification of neuronal alpha-tubulin which consists of the posttranslational addition of a varying number of glutamyl units on the gamma-carboxyl group of glutamate residue 445. This modification, called polyglutamylation, was initially found associated with detyrosinated alpha-tubulin [Eddé, B., Rossier, J., Le Caer, J.P., Desbruyères, E., Gros, F., & Denoulet, P. (1990) Science 247, 83-85]. In this report we show that a lateral chain of glutamyl units can also be present on tyrosinated alpha-tubulin. Incubation of cultured mouse brain neurons with radioactive tyrosine, in the presence of cycloheximide, resulted in a posttranslational labeling of six alpha-tubulin isoelectric variants. Because both tyrosination and polyglutamylation occur in the C-terminal region of alpha-tubulin, the structure of this region was investigated. [3H]tyrosinated tubulin was mixed with a large excess of unlabeled mouse brain tubulin and digested with thermolysin. Five peptides, detected by their radioactivity, were purified by high-performance liquid chromatography. Amino acid sequencing and mass spectrometry showed that one of these peptides corresponds to the native C-terminal part of alpha-tubulin 440VEGEGEEEGEEY451 and that the remainders bear a varying number of glutamyl units linked to glutamate residue 445, which explains the observed heterogeneity of tyrosinated alpha-tubulin. A quantitative analysis showed that the different tyrosinated forms of alpha-tubulin represent a minor (13%) fraction of the total alpha-tubulin present in the brain and that most (80%) of these tyrosinated forms are polyglutamylated.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure of tubulin C-terminal domain obtained by subtilisin treatment The major α and β tubulin isotypes from pig brain are glutamylated

Limited subtilisin digestion of the tubulin alpha, beta heterodimer has been used in this work to reduce the total number of tubulin isotypes from 20 for native to 9 for subtilisin-cleaved tubulin. This indicates that the major part of tubulin heterogeneity is located at the C-terminus of the molecule. The C-terminal peptides of both alpha and beta subunits of tubulin were purified by anion-exchange HPLC. Combined use of Edman degradation chemistry and mass spectrometry on the isolated peptides shows that subtilisin cleavage occurs at position Asp-438 and His-406 of alpha and Gln-433 and His-396 of beta tubulin chains. Quantitative analysis of our data show that cleavage at positions His-406 (alpha) and His-396 (beta) occurs with a low efficiency and indicates that the major isotypes of pig brain tubulin are modified by sequential attachment of 1 to 5 glutamic acid residues at positions Glu-445 or -435 of alpha and beta tubulin, respectively.

Ca2+-myristoyl switch and membrane binding of chemically acylated neurocalcins

Neurocalcin is a member of a novel family of neuronal calcium sensors that belongs to the superfamily of EF-hand Ca(2+)-binding proteins. Neurocalcin is myristoylated on its N-terminus in vivo and can associate with biological membranes in a calcium and myristoyl-dependent manner. This process known as "Ca(2+)-myristoyl switch" has been best described for the photoreceptor specific protein, recoverin, as well as for several other neuronal calcium sensors. Here, we used reversed micelles to chemically acylate nonmyristoylated neurocalcin at its N-terminus with fatty acids of different lengths (from C12 to C16). This approach allowed us to prepare neurocalcin derivatives in which a single fatty acid is selectively linked to the N-terminal glycine of the polypeptide chain through an amide bond. The membrane binding properties of the monoacylated neurocalcins were then examined by cosedimentation with phospholipid vesicles and direct binding to lipid monolayers by surface plasmon resonance spectroscopy (Biacore). Our results show that neurocalcins monoacylated with lauric, myristic, or palmitic acid were able to associate with membrane in a calcium-dependent manner. This indicates that the Ca(2+)-myristoyl switch can function with different lipid moieties and is not strictly restricted to myristate. The ability to modify at will the fatty acid linked to the N-terminal glycine should be useful to analyze the contribution of the fatty acid moiety to the biological function of this family of neuronal calcium sensors.

Selection and identification of proteins bound to DNA triple-helical structures by combination of 2D-electrophoresis and MALDI-TOF mass spectrometry

Identification of proteins binding specifically to peculiar nucleic acid structures can lead to comprehension of their role in vivo and contribute to the discovery of structure-related gene regulation. This work was devoted to establishing a reliable procedure to select proteins on the basis of their interaction with a nucleic acid probe chosen to fold into a given structure. 2D-electrophoresis and mass spectrometry were combined for protein identification. We applied this procedure to select and identify triplex-binding activities in HeLa nuclear extracts. To achieve this, we used a panel of deoxyribonucleic probes adopting intramolecular triple-helices, varying in their primary sequence, structure or triple-helix motif. A limited number of spots was reproducibly revealed by South-western blotting. Spots of interest were localised among a complex population of (35)S-labelled proteins according to their (32)P-specific emission. Position of the same spots was extrapolated on a preparative gel coloured with Coomassie blue, allowing excision and purification of the corresponding proteins. The material was subjected to mass spectrometry upon trypsin digestion and MALDI-TOF peptide fingerprinting was used for research in databases: five of them were identified and found to belong to the hnRNP family (K, L, A2/B1, E1 and I). The identities of several of them were confirmed by comparing western and South-western blots on the same membrane using specific antibodies. The recognition specificity of most of these proteins is large, according to previous reports and our own experiments. It includes pyrimidine-rich DNA sequences in different contexts: single strand to a small extent, triplex and possibly other higher-order structures.

Ponericins, new antibacterial and insecticidal peptides from the venom of the ant Pachycondyla goeldii

The antimicrobial, insecticidal, and hemolytic properties of peptides isolated from the venom of the predatory ant Pachycondyla goeldii, a member of the subfamily Ponerinae, were investigated. Fifteen novel peptides, named ponericins, exhibiting antibacterial and insecticidal properties were purified, and their amino acid sequences were characterized. According to their primary structure similarities, they can be classified into three families: ponericin G, W, and L. Ponericins share high sequence similarities with known peptides: ponericins G with cecropin-like peptides, ponericins W with gaegurins and melittin, and ponericins L with dermaseptins. Ten peptides were synthesized for further analysis. Their antimicrobial activities against Gram-positive and Gram-negative bacteria strains were analyzed together with their insecticidal activities against cricket larvae and their hemolytic activities. Interestingly, within each of the three families, several peptides present differences in their biological activities. The comparison of the structural features of ponericins with those of well-studied peptides suggests that the ponericins may adopt an amphipathic alpha-helical structure in polar environments, such as cell membranes. In the venom, the estimated peptide concentrations appear to be compatible with an antibacterial activity in vivo. This suggests that in the ant colony, the peptides exhibit a defensive role against microbial pathogens arising from prey introduction and/or ingestion.

An optimized procedure for detection of proteins on carrier ampholyte isoelectric focusing and immobilized pH gradient gels with imidazole and zinc salts: its application to the identification of isoelectric focusing separated isoforms by in-gel proteolysis and mass spectrometry analysis

A method for the characterization of proteins separated by isoelectric focusing in carrier ampholytes (CA-IEF) or immobilized pH gradient (IPG) gels by in-gel digestion and mass spectrometry is described. Proteins are detected by an improved imidazole-Sodium dodecyl sulfate (SDS)-zinc staining adapted for IEF and IPG gels. Sensitivity is close to that of mass spectrometry-compatible silver staining, but simpler and faster. Proteins were digested in imidazole-SDS-zinc stained CA-IEF and IPG gels in the presence of a zinc-chelating agent. Mass spectra were clearly interpretable as carrier ampholytes which were efficiently removed before digestion; high-sequence coverage that allowed isoform characterization was obtained by analyzing both the aqueous and the organic phase extracts.

Large-scale monitoring of pleiotropic regulation of gene expression by the prokaryotic nucleoid-associated protein, H-NS

Despite many years of intense work investigating the function of nucleoid-associated proteins in prokaryotes, their role in bacterial physiology remains largely unknown. The two-dimensional protein patterns were compared and expression profiling was carried out on H-NS-deficient and wild-type strains of Escherichia coli K-12. The expression of approximately 5% of the genes and/or the accumulation of their protein was directly or indirectly altered in the hns mutant strain. About one-fifth of these genes encode proteins that are involved in transcription or translation and one-third are known to or were in silico predicted to encode cell envelope components or proteins that are usually involved in bacterial adaptation to changes in environmental conditions. The increased expression of several genes in the mutant resulted in a better ability of this strain to survive at low pH and high osmolarity than the wild-type strain. In particular, the putative regulator, YhiX, plays a central role in the H-NS control of genes required in the glutamate-dependent acid stress response. These results suggest that there is a strong relationship between the H-NS regulon and the maintenance of intracellular homeostasis.

Towards a proteomic map of Lactococcus lactis NCDO 763

Lactococcus lactis is a widely used bacteria in dairy industry, specially in cheese ripening. Numerous lactococcal enzymes and proteins are involved in this process. Proteomics makes it possible to deal with a high number of proteins and identify modification of their patterns in two-dimensional (2-D) gels. However, an annotated reference map is necessary prior to analyzing protein variations. We have begun to construct such a map in easily reproducible conditions and identify proteins.

Specific Ser-Pro phosphorylation by the RNA-recognition motif containing kinase KIS

We present here a first appraisal of the phosphorylation site specificity of KIS (for 'kinase interacting with stathmin'), a novel mammalian kinase that has the unique feature among kinases to possess an RNP type RNA-recognition motif (RRM). In vitro kinase assays using various standard substrates revealed that KIS has a narrow specificity, with myelin basic protein (MBP) and synapsin I being the best in vitro substrates among those tested. Mass spectrometry and peptide sequencing allowed us to identify serine 164 of MBP as the unique site phosphorylated by KIS. Phosphorylation of synthetic peptides indicated the importance of the proline residue at position +1. We also identified a tryptic peptide of synapsin I phosphorylated by KIS and containing a phosphorylatable Ser-Pro motif. Altogether, our results suggest that KIS preferentially phosphorylates proline directed residues but has a specificity different from that of MAP kinases and cdks.

S-adenosylmethionine decarboxylase of Bacillus subtilis is closely related to archaebacterial counterparts

Bacillus subtilis synthesizes polyamines by decarboxylating arginine to agmatine, which is subsequently hydrolysed to putrescine. Spermidine is synthesized from putrescine and decarboxylated S-adenosylmethionine (dAdoMet). In Gram-negative bacteria and in eukaryotes, AdoMet is decarboxylated by an unusual 'pyruvoyl' AdoMet decarboxylase (SpeD), the catalytic pyruvoyl moiety of which is generated by serinolysis of an internal serine with self-cleavage of the protein at the upstream peptide bond. Neither the Gram-positive bacterial nor the archaeal counterpart of the Escherichia coli SpeD enzyme were known. We have identified the corresponding B. subtilis speD gene (formely ytcF). Heterologous expression of the cognate Methanococcus jannaschii protein, MJ0315, demonstrated that it displays the same activity as B. subtilis SpeD, indicating that spermidine biosynthesis in Gram-positive bacteria and in archaea follows a pathway very similar to that of Gram-negatives and eukarya. In B. subtilis, transcription of speD is modulated by spermidine and methionine. Its expression is high under usual growth conditions. In contrast, the SpeD protein self-cleaves slowly in vitro, a noticeable difference with its archaeal counterpart. Under certain growth conditions (minimal medium containing succinate and glutamate as a carbon source), speD is co-transcribed with gapB, the gene encoding glyceraldehyde-3-phosphate dehydrogenase, an enzyme required for gluconeogenesis. This observation may couple polyamine metabolism to sulphur and carbon metabolism by a so far unknown mechanism.

Characterization of a human angiotensinogen cleaved in its reactive center loop by a proteolytic activity from Chinese hamster ovary cells

Angiotensinogen, the renin (E.C. 3.4.23.15) substrate, belongs to the serpins superfamily and has been classified as a noninhibitory serpin. Using mass spectroscopy, angiotensinogen purified from Chinese hamster ovary cell supernatant shows a broad spectrum. The absence of protease inhibitors throughout the purification leads to an angiotensinogen cleaved within the reactive center loop. This cleavage does not affect the Ang I generation because kinetic parameters are similar to the values of the full-length angiotensinogen. Although cleavage is complete, the cleaved angiotensinogen migrates after deglycosylation on SDS-polyacrylamide gel electrophoresis as a doublet differing by 4 kDa. To test whether the circulating angiotensinogen is cleaved in the reactive center loop, it was purified from a pool of human plasma and was shown to be uncleaved. Its migration was obviously slower than of cleaved angiotensinogen but also consisted of two bands pointing to a so far unexplained residual heterogeneity. We then compared the heat-induced polymerization of full-length- and reactive center loop-cleaved angiotensinogens. Both monomers were able to aggregate, revealing a particular behavior of angiotensinogen distinct from that of reactive center loop-cleaved serpins. Lacking the three-dimensional structure of angiotensinogen, we propose and discuss a structural model of the serpin fold within the renin substrate.

Biophysical characterization of lithostathine. Evidences for a polymeric structure at physiological pH and a proteolysis mechanism leading to the formation of fibrils

Lithostathine is a calcium carbonate crystal habit modifier. It is found precipitated under the form of fibrils in chronic calcifying pancreatitis or Alzheimer's disease. In order to gain better insight into the nature and the formation of fibrils, we have expressed and purified recombinant lithostathine. Analytical ultracentrifugation and quasi-elastic light scattering techniques were used to demonstrate that lithostathine remains essentially monomeric at acidic pH while it aggregates at physiological pH. Analysis of these aggregates by electron microscopy showed an apparently unorganized structure of numerous monomers which tend to precipitate forming regular unbranched fibrils. Aggregated forms seem to occur prior to the apparition of fibrils. In addition, we have demonstrated that these fibrils resulted from a proteolysis mechanism due to a specific cleavage of the Arg(11)-Ile(12) peptide bond. It is deduced that the NH(2)-terminal undecapeptide of lithostathine normally impedes fiber formation but not aggregation. A theoretical model explaining the formation of amyloid plaques in neurodegenerative diseases or stones in lithiasis starting from lithostathine is described. Therefore we propose that lithostathine, whose major function is unknown, defines a new class of molecules which is activated by proteolysis and is not involved in cytoskeleton nor intermediate filament functions.

Treatment with crystalline ultra-pure urea reduces the aggregation of integral membrane proteins without inhibiting N-terminal sequencing

We have demonstrated that N-terminal sequencing can be performed successfully despite boiling protein samples in the presence of urea under precise conditions, before loading them onto SDS-PAGE and transfer to polyvinylidene difluoride membrane. Using myoglobin as a test protein, we found that its ability to undergo N-terminal sequencing was not affected by the presence of urea provided "ultra-pure" urea was used. Consistent with this result, we verified that urea did not carbamylate myoglobin since its molecular mass was measured by mass spectrometry after electroelution of the protein band from the gel. These observations are useful for the study of integral membrane proteins, in particular to study their topology from proteolysis experiments, since heating in the presence of urea before SDS-PAGE reduces membrane protein aggregation [Soulié, S., Mo/ller, J.V., Falson, P., and le Maire, M. (1996) Anal. Biochem. 236, 363-364]. We show that the sequencing yield of a hydrophobic peptide from reticulum Ca2+-ATPase was more than doubled in the presence of urea in accord with the quantification of the Coomassie Blue staining of the gel and of the amount present on the polyvinylidene difluoride membrane. For three peptides of the gastric H+K+-ATPase, the sequencing yield after urea treatment increased almost threefold.

Structure, synthesis, and molecular cloning of dermaseptins B, a family of skin peptide antibiotics

Analysis of antimicrobial activities that are present in the skin secretions of the South American frog Phyllomedusa bicolor revealed six polycationic (lysine-rich) and amphipathic alpha-helical peptides, 24-33 residues long, termed dermaseptins B1 to B6, respectively. Prepro-dermaseptins B all contain an almost identical signal peptide, which is followed by a conserved acidic propiece, a processing signal Lys-Arg, and a dermaseptin progenitor sequence. The 22-residue signal peptide plus the first 3 residues of the acidic propiece are encoded by conserved nucleotides encompassed by the first coding exon of the dermaseptin genes. The 25-residue amino-terminal region of prepro-dermaseptins B shares 50% identity with the corresponding region of precursors for D-amino acid containing opioid peptides or for antimicrobial peptides originating from the skin of distantly related frog species. The remarkable similarity found between prepro-proteins that encode end products with strikingly different sequences, conformations, biological activities and modes of action suggests that the corresponding genes have evolved through dissemination of a conserved "secretory cassette" exon.

Human tyrosine hydroxylase isoforms. Inhibition by excess tetrahydropterin and unusual behavior of isoform 3 after camp-dependent protein kinase phosphorylation

Human tyrosine hydroxylase exists as four isoforms (hTH1-4), generated by alternative splicing of pre-mRNA, with tissue-specific distribution. Unphosphorylated hTH3 and hTH1 were produced in large amounts in Escherichia coli and purified to homogeneity. The phosphorylation sites were determined after labeling with [32P]phosphate in the presence of cAMP-dependent protein kinase (PKA) and calmodulin-dependent protein kinase II (CaM-PKII). Ser40 was phosphorylated by PKA, and both Ser19 and Ser40 were phosphorylated by CaM-PKII. The enzyme kinetics of hTH3 were determined in the presence of various concentrations of the natural co-substrate (6R)-tetrahydrobiopterin and compared with those of recombinant hTH1 (similar to rat TH). We show that, under initial velocity conditions, excess (6R)-tetrahydrobiopterin inhibits hTH3 and hTH1. The TH catalytic constants (kcat) were determined for each of the two isoenzymes: hTH3 is about five times more active than hTH1. Phosphorylation by CaM-PKII did not affect the kinetic parameters of hTH3. The classical activation of TH by PKA phosphorylation, demonstrated for hTH1, was not observed with hTH3. Furthermore, hTH3 escapes activity regulation by phosphorylation and is always more active than phosphorylated hTH1. The properties of the hTH3 enzyme may be relevant to diseases affecting dopaminergic cells.

Cysteinyl-tRNA synthetase from Saccharomyces cerevisiae. Purification, characterization and assignment to the genomic sequence YNL247w

Cysteinyl-tRNA synthetase (CRS) from Saccharomyces cerevisiae was purified 2300-fold with a yield of 33%, to a high specific activity (kcat4.3 s-1 at 25 degrees C for the aminoacylation of yeast tRNACys). SDS-PAGE revealed a single polypeptide corresponding to a molecular mass of 86 kDa. Polyclonal antibodies to the purified protein inactivated CRS activity and detected only one polypeptide of 86 kDa in a yeast extract subjected to SDS-PAGE followed by immunoblotting. In contrast to bacterial CRS which is a monomer of about 50 kDa, the native yeast enzyme behaved as a dimer, as assessed by gel filtration and cross-linking. Its subunit molecular mass is in good agreement with the value of 87.5 kDa calculated for the protein encoded by the yeast genomic sequence YNL247w. The latter was previously tentatively assigned to CRS, based on limited sequence similarities to the corresponding enzyme from other sources. Determination of the amino acid sequence of internal polypeptides derived from the purified yeast enzyme confirmed this assignment. Alignment of the primary sequences of prokaryotic and yeast CRS reveals that the larger size of the latter is accounted for mostly by several insertions within the sequence.

Multiple bacteriocin production by Leuconostoc mesenteroides TA33a and other Leuconostoc/Weissella strains

Leuconostoc (Lc.) mesenteroides TA33a produced three bacteriocins with different inhibitory activity spectra. Bacteriocins were purified by adsorption/desorption from producer cells and reverse phase high-performance liquid chromatography. Leucocin C-TA33a, a novel bacteriocin with a predicted molecular mass of 4598 Da, inhibited Listeria and other lactic acid bacteria (LAB). Leucocin B-TA33a has a predicted molecular mass of 3466 Da, with activity against Leuconostoc/Weissella (W.) strains, and appears similar to mesenterocin 52B and dextranicin 24, while leucocin A-TA33a, which also inhibited Listeria and other LAB strains, is identical to leucocin A-UAL 187. A survey of other known bacteriocin-producing Leuconostoc/Weissella strains for the presence of the three different bacteriocins revealed that production of leucocin A-, B- and C-type bacteriocins was widespread. Lc. carnosum LA54a, W. paramesenteroides LA7a, and Lc. gelidum UAL 187-22 produced all three bacteriocins, whereas W. paramesenteroides OX and Lc. carnosum TA11a produced only leucocin A- and B-type bacteriocins.

Characterization of the chicken telokin heterogeneity by time-of-flight mass spectrometry

Chicken gizzard telokin was purified to apparent homogeneity by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This preparation yielded upon mass spectrometry analysis seven mass peaks spanning from 15 858 to 17 100 Da. Anion exchange-high performance liquid chromatography of the purified telokin revealed a high diversity of telokin molecules. By combining protein chemistry to chromatography and mass spectrometry, the telokin heterogeneity was analyzed. Three acetylated N-termini were found, AMI, MIS, and SGR. Cyanogen bromide cleavage of telokin yielded six different C-terminal peptides corresponding to the removal of one to six C-terminal glutamyl residues from the protein sequence deduced from the cDNA. Phosphorylation of telokin was detected, thus increasing the heterogeneity of the telokin preparation. In addition, peptide sequencing has shown that telokin contained either an aspartyl or a glutamyl residue at position 27, probably resulting from chicken polymorphism.

mRNP3 and mRNP4 are phosphorylatable by casein kinase II in Xenopus oocytes, but phosphorylation does not modify RNA-binding affinity

mRNP3 and mRNP4 (also called FRGY2) are two mRNA-binding proteins which are major constituents of the maternal RNA storage particles of Xenopus laevis oocytes. The phosphorylation of mRNP3-4 has been implicated in the regulation of mRNA masking. In this study, we have investigated their phosphorylation by casein kinase II and its consequence on their affinity for RNA. Comparison of the phosphopeptide map of mRNP3-4 phosphorylated in vivo with that obtained after phosphorylation in vitro by purified Xenopus laevis casein kinase II strongly suggests that casein kinase II is responsible for the in vivo phosphorylation of mRNP3-4 in oocytes. The phosphorylation occurs on a serine residue in a central domain of the proteins. The affinity of mRNP3-4 for RNA substrates remained unchanged after the treatment with casein kinase II or calf intestine phosphatase in vitro. This suggests that phosphorylation of these proteins does not regulate their interaction with RNA but rather controls their interactions with other proteins.

Lysozyme fragmentation induced by gamma-radiolysis

Irradiation of lysozyme in frozen states in the absence of oxygen induces specific fragmentation at defined sites along the backbone chain. This paper localizes radio-fragmentation sites by two methods. First, N-terminal sequencing of radiolysis fragments after separation by SDS-polyacrylamide gel electrophoresis and estimation of their molecular masses. Secondly, after purification of radiolysis fragments by reverse phase-HPLC and determination of their molecular mass by electro-spray-ionization mass-spectrometric analysis, combined to N-terminal sequencing and total amino acid analysis. Evidence for the breakage of the peptide bond itself (CO-NH) is given, with radio-fragmentation sites mostly found at the surface of irradiated lysozyme in solvent exposed loops and turns.

Posttranslational modifications of axonemal tubulin

Axonemal tubulin exhibits a high degree of heterogeneity mostly due to several posttranslational modifications (PTM). The aim of this work was to chemically characterize the different PTM occurring in the C-terminal tail of axonemal tubulin purified from sea urchin, Paracentrotus lividus, spermatozoa. After its purification, tubulin was enzymatically cleaved. The C-terminal peptides were chromatographically isolated, first by anion exchange and then by reverse-phase HPLC. Peptides were characterized by their sequence, determined by Edman degradation, and by their mass, determined by MALDI-TOF/MS. The two major conclusions are that the majority of the isolated C-terminal peptides were unmodified and that polyglycylation and polyglutamylation can occur simultaneously on one molecule of alpha-tubulin.

Human coproporphyrinogen oxidase. Biochemical characterization of recombinant normal and R231W mutated enzymes expressed in E. coli as soluble, catalytically active homodimers

To obtain recombinant human coproporphyrinogen oxidase (CPX), a cDNA for the coding region of mature human CPX has been expressed in E. coli. CPX was produced as a fusion protein with glutathione S-transferase followed by the hexapeptide recognition site for thrombin cleavage just preceding first amino acid of the CPX protein. The human CPX was found to be in the soluble fraction. This previously unobtainable human heme synthetic enzyme was purified to electrophoretic homogeneity with a specific activity of 4200 nmol/hr./mg of protein using a Glutathione Sepharose 4B column and gel filtration. Recombinant human CPX exhibits homogeneous behavior during high performance liquid chromatography (HPLC) and the N-terminal sequence, confirmed by protein sequencing, revealed a single polypeptide chain. In its active form, human CPX is a homodimer. According to the hydrodynamic properties derived from analytical ultracentrifugation, dimeric CPX has a nearly globular shape. Additionally, naturally occurring Arg to Trp (R231W)-mutated CPX has been also expressed in E. coli and further characterized. The mutated enzyme has a Km value of 0.55 microM as compared to 0.30 microM for the wild type. The catalytic efficiency (specificity constant, kcat/Km) of the mutated CPX was four fold lower than wild-type enzyme. The activity measurement of the mutated enzyme showed higher thermal sensitivity as compared with wild type CPX. The measured pI for mutated CPX is 5.65, compared to 6.40 for wild type. The pH optima for the mutated and wild-type protein are 6.6 and 6.8, respectively. The R231W mutation of CPX does not affect dimer formation and both normal and mutated CPX exhibit identical sedimentation properties. The thermal denaturation of both wild type and mutant CPX was found to be irreversible. The mutated CPX contained a significant amount of tightly bound porphyrin coproporphyrin. No metal association was found either in wild type or in mutated CPX. The availability of the recombinant human CPX will aid in structural and mechanistic studies.

Identification of calreticulin-like protein as one of the phosphoproteins modulated in response to oligogalacturonides in tobacco cells

Oligogalacturonide-induced modifications of protein phosphorylation in cells of Nicotiana tabacum L. were investigated by in-vitro phosphorylation of plasma-membrane-enriched fractions and electrophoretic analysis on two-dimensional gels. About 100 polypeptides were resolved; among these 40 phosphoproteins were detected and their 33P-labelling quantified. Most of the phosphorylations were inhibited by staurosporine and several proteins were hyperphosphorylated in the presence of okadaic acid, indicating the presence of protein phosphatase(s) in addition to staurosporine-susceptible protein kinase(s) in the plasma-membrane-enriched fraction. In the presence of oligogalacturonides, phosphorylation of seven acidic polypeptides ranging from 15 to 65 kDa was strongly enhanced. A twofold enhancement of the phosphorylation of 24-kDa protein and a two- to threefold decrease in the phosphorylation of acidic proteins of MrS 62, 65, 80 and 84 was also observed in response to oligogalacturonides. One of the oligogalacturonide-modulated phosphoproteins was identified as calreticulin by direct nucleotide sequencing after preparative two-dimensional electrophoresis and comparison with protein database sequences. Decreased phosphorylation of calreticulin was also observed in vivo, shortly after addition of oligogalacturonides to tobacco cells, confirming the biological relevance of the modification. Although the presence of calreticulin, an abundant reticuloplasmin with high calcium-binding capacity, has been reported in both mammalian and plant cells, its function is as yet largely unknown. Modulation of the phosphorylation of a plant calreticulin-like protein by oligogalacturonides is shown here, suggesting a role in the early transduction steps of this signal.

Characterization of hyperglycemic and molt-inhibiting activity from sinus glands of the penaeid shrimp Penaeus vannamei

To design a homologous bioassay for the molt-inhibiting hormone and the crustacean hyperglycemic hormone of the shrimp Penaeus vannamei, the effect of sinus gland homogenate (SGh), in vitro, on ecdysteroid production by Y-organs (YOs), and the effect of the injection of SGh, in vivo, on the glycemia of shrimps have been investigated. Addition of SGh to incubation medium of shrimp YOs dose dependently reduced, within a few hours, ecdysteroid release into the medium. Moreover, inhibition by SGh decreases drastically in YOs from animals in late premolt stages, when there is maximal ecdysteroid production. Injection of SGh into shrimps evokes a hyperglycemic response maximal after 2 hr. Immunoadsorption of SGh with an anti-Homarus americanus cHHA antiserum inhibited both biological activities of the homogenate. After fractionation of acidic sinus gland extract by RP-HPLC, the maximal response in both bioassays was associated with the major UV absorbent peak, which was also the major immunoreactive peak when tested by ELISA with the anti-lobster cHHA. After a further purification step, the molecular mass of the bioactive and immunoreactive peptide was found to be 8627 +/- 0.3 Da by electrospray ionization mass spectrometry. The amino acid sequence of the first 38 residues of this peptide was established by gas-phase microsequencing. This sequence shows 55% homology with the first 38 residues of the lobster cHHA.

Covalent structure, synthesis, and structure-function studies of mesentericin Y 105(37), a defensive peptide from gram-positive bacteria Leuconostoc mesenteroides

A 37-residue cationic antimicrobial peptide named mesentericin Y 105(37) was purified to homogeneity from cell-free culture supernatant of the Gram-positive bacterium Leuconostoc mesenteroides. The complete amino acid sequence of the peptide, KYYGNGVHCTKSGCSVNWGEAASAGIHRLANGGNGFW, has been established by automated Edman degradation, mass spectrometry, and solid phase synthesis. Mesentericin Y 105(37) contains a single intramolecular disulfide bond that forms a 6-membered ring within the molecule. Mesentericin Y 105(37) was synthesized by the solid phase method. The synthetic replicate was shown to be indistinguishable from the natural peptide with respect to electrophoretic and chromatographic properties, mass spectrometry analysis, automated amino acid sequence determination, and antimicrobial properties. At nanomolar concentrations, synthetic mesentericin Y 105(37) is active against Gram+ bacteria in the genera Lactobacillus and Carnobacterium. Most interestingly, the peptide is inhibitory to the growth of the food-borne pathogen Listeria. CD spectra of mesentericin Y 105(37) in low polarity medium, which mimic the lipophilicity of the membrane of target organisms, indicated 30-40% alpha-helical conformation, and predictions of secondary structure suggested that the peptide can be configured as an amphipathic helix spanning over residues 17-31. To reveal the molecular basis of the specificity of mesentericin Y 105(37) targetting and mode of action, NH2- or COOH-terminally truncated analogs together with point-substituted analogs were synthesized and evaluated for their ability to inhibit the growth of Listeria ivanovii. In sharp contrast with broad spectrum alpha-helical antimicrobial peptides from vertebrate animals, which can be shortened to 14-18 residues without deleterious effect on potency, molecular elements responsible for anti-Listeria activity of mesentericin Y 105(37) are to be traced at once to the NH2-terminal tripeptide KYY, the disulfide bridge, the putative alpha-helical domain 17-31, and the COOH-terminal tryptophan residue of the molecule. It is proposed that the amphipathic helical domain of the peptide interacts with lipid bilayers, leading subsequently to alteration of the membrane functions, whereas residues 1-14 form part of a recognition structure for a membrane-bound receptor, which may be critical for peptide targetting. Because mesentericin Y 105(37) is easy to synthesize at low cost, it may represent a useful and tractable tool as a starting point for the design of more potent analogs that may be of potential applicability in foods preservation.

Characterization of centrin genes in Paramecium

Centrins are highly conserved, ubiquitous cytoskeletal components which belong to the EF-hand superfamily of Ca2+-modulated proteins. We report here the molecular characterization of new members of the centrin family, Paramecium centrins. Previous studies described the organization of the infraciliary lattice (ICL), the innermost cortical cytoskeletal network of Paramecium, and showed that it was composed of a set of low-molecular-mass, Ca2+-binding polypeptides [Garreau de Loubresse, N., Klotz, C., Vigues, B., Rutin, J & Beisson, J. (1991) Biol. Cell 71, 217-225]. In this paper we show that these polypeptides are recognized by specific anti-centrin polyclonal antibodies. Their microsequences revealed four distinct N-termini. For one of them, ICL1, N-terminal and internal peptide sequences were used for PCR amplification and cloning of a DNA fragment containing a complete centrin coding sequence. The deduced amino acid sequence presents about 50% identify with those of centrins from other species. Further molecular analysis allowed us to identify two additional closely related, co-expressed ICL1 genes, providing the first example of a centrin multigenic family in a microorganism.

Characterization of a novel elastase inhibitor from a fan coral

An acidic hydromethanolic extract of the tropical gorgonian Melithea cf. stormii exhibited anti-elastase activity. From the polypeptidic mixture we isolated and purified to homogeneity a protein with a molecular mass determined at 21,159 Da by Maldi/Tof mass spectrometric analysis. The novel protein of marine invertebrate origin strongly inhibited amidolysis of Suc(Ala) 3pNA by porcine pancreatic elastase (PPE) and was labelled iela melst. The N-terminal aminoacid sequence of its 39-first residues revealed the characteristics of a non-classical Kazal-type domain. Iela melst behaved as a reversible tight-binding inhibitor of PPE. The competitive inhibition followed Cha's mechanism A with an equilibrium dissociation constant, Ki, calculated as 1.5 x 10(-9) M.

Posttranslational modifications in the C-terminal tail of axonemal tubulin from sea urchin sperm

After proteolytic digestion of sperm tubulin from sea urchin Paracentrotus lividus, C-terminal peptides were isolated by chromatographic separations. The peptides were analyzed by Edman degradation and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. About 70% of the isolated C-terminal peptides were unmodified. The remaining modified peptides have undergone a combination of numerous posttranslational modifications generating significant heterogeneity of sperm tubulin. alpha-Tubulin is modified by detyrosylation, release of the penultimate glutamate, polyglutamylation, and polyglycylation. Glycylation and glutamylation can coexist within one alpha-tubulin isoform. beta-Tubulin undergoes polyglycylation but was not observed to be polyglutamylated. The number of units posttranslationally added reaches 11 and 12 glycyl units on beta- and alpha-tubulin, respectively. This is different from the polyglycylation of axonemal tubulin in Paramecium cilia where up to 40 added glycyl units were observed both on alpha- and beta-tubulin.

Purification, in vitro reassembly, and preliminary sequence analysis of epiplasmins, the major constituent of the membrane skeleton of Paramecium

The epiplasmic layer, a continuous rigid granulo-fibrillar sheet directly subtending the surface membranes of Paramecium, is one of the outermost of the various cytoskeletal networks that compose it cortex. We have previously shown that the epiplasm consists of a set of 30 to 50 protein bands on SDS-PAGE in the range 50 to 33 kDa, the epiplasmins. We report a purification procedure for the set of epiplasmic proteins, a description of their physicochemical and reassembly properties, and a preliminary characterization of their sequence. The conditions for solubilization of the epiplasm and for in vitro reassembly of its purified constituents ar described. Reassembly of the entire set of proteins and of some (but not all) subsets are shown to yield filamentous aggregates. Microsequences of two purified bands of epiplasmins reveal a striking amino acid sequence consisting of heptad repeats of only three main amino acids, P, V, and Q. These repeats were confirmed by DNA sequencing of polymerase chain reaction products. The motif is QPVQ-h, in which h is a hydrophobic residue. This may constitute the core of the epiplasmin sequence and, in view of the tendency of such a sequence to form a coiled-coil, may account for the remarkable self-aggregation properties of epiplasmins.

The relationships between the toxicity and the primary and secondary structures of elicitinlike protein elicitors secreted by the phytopathogenic fungus Pythium vexans

Elicitins are toxic and signaling proteins secreted by Phytophthora spp. responsible for the incompatible reaction and systemic hypersensitive-like necroses of diverse plant species leading to resistance against fungal or bacterial plant pathogens. Such proteins were observed in the culture filtrate of another species of the Oomycete genus, Pythium vexans. Two alpha elicitinlike proteins were purified and sequenced. One of these novel elicitins (Vex2) exhibited a 100-residue sequence instead of 98 while the other (Vex1) had an N-glycosylation site, effectively glycosylated (equivalent of 16 hexose residues). In addition to the point mutations already observed in Phytophthora species, we found several novel amino acid changes. Furthermore, circular dichroism revealed some differences in their structure in solution compared with the Phytophthora elicitins that were correlated with specific point mutations. These sequences permitted the establishment of a phylogenic tree, suggesting that Pythium vexans is a species close to the Phytophthora genus. The toxicity of the Pythium vexans elictins to tobacco leaves was investigated and correlated with the occurrence of the carbohydrate moiety of one of the two isoforms, observed for the first time in an elicitin.

ERGIC-53, a membrane protein of the endoplasmic reticulum-Golgi intermediate compartment, is identical to MR60, an intracellular mannose-specific lectin of myelomonocytic cells

A mannose-specific membrane lectin (MR60) isolated from human myelomonocytic HL60 cells by affinity chromatography is expressed in intracellular organelles of immature monocytes (Pimpaneau, V., Midoux, P., Monsigny, M., and Roche, A. C. (1991) Carbohydr. Res. 213, 95-108). It is not present at the cell surface and is immunochemically and structurally distinct from the M(r) 175,000 mannose receptor of mature macrophages. MR60 cDNA was isolated and characterized; on the basis of its sequence, MR60 is not related to any known mammalian lectins. Surprisingly, MR60 was found to be identical to ERGIC-53 (Schindler, R., Itin, C., Zerial, M., Lottspeich, F., and Hauri, H.P. (1993) Eur. J. Cell Biol. 61, 1-9), a type I integral membrane protein, defined as a marker of the intermediate compartment that recycles between the Golgi apparatus and endoplasmic reticulum; MR60/ERGIC-53 shares with VIP-36 significant homologies with leguminous plant lectins (Fiedler, K., and Simmons, K. (1994) Cell 77, 625-626). We extend these findings in evidencing a structural homology between MR60/ERGIC-53 and mammalian galectins (soluble beta galactose binding proteins). MR60/ERGIC-53 is the first lectin characterized as an endoplasmic reticulum-Golgi protein. Accordingly, this intracellular mannose binding protein could be involved in the traffic of glycoproteins between endoplasmic reticulum and the Golgi apparatus.

Electrospray mass spectrometry for the characterization of the purity of natural and modified oligodeoxynucleotides

Electrospray ionization mass spectrometry is an accurate and sensitive analytical method to characterize the purity of oligodeoxynucleotides being tested for pharmacological studies. We report the preparation procedure ('desalting') of natural and modified oligodeoxynucleotides (ODNs) and their analysis by negative-ion electrospray mass spectrometry. We evaluate the sensitivity and the accuracy of the method for two antisense ODN sequences. Mass analysis of the 25-mer phosphorothioate can be performed to within 0.001% accuracy (standard error of 0.05 Da) for a sample concentration of 12 pmol/microL. In addition, the adduct ion and the failure sequence can be identified to characterize the antisense ODN.

Purification of arginase from Aspergillus nidulans

Arginase (EC 3.5.3.1) of Aspergillus nidulans, the enzyme which enables the fungus to use arginine as the sole nitrogen source was purified to homogeneity. Molecular mass of the purified arginase subunit is 40 kDa and is similar to that reported for the Neurospora crassa (38.3 kDa) and Saccharomyces cerevisiae (39 kDa) enzymes. The native molecular mass of arginase is 125 kDa. The subunit/native molecular mass ratio suggests a trimeric form of the protein. The arginase protein was cleaved and partially sequenced. Two out of the six polypeptides sequenced show a high degree of homology to conserved domains in arginases from other species.

Polyglycylation of tubulin: a posttranslational modification in axonemal microtubules

A posttranslational modification was detected in the carboxyl-terminal region of axonemal tubulin from Paramecium. Tubulin carboxyl-terminal peptides were isolated and analyzed by Edman degradation sequencing, mass spectrometry, and amino acid analysis. All of the peptides, derived from both alpha and beta tubulin subunits, were modified by polyglycylation, containing up to 34 glycyl units covalently bound to the gamma carboxyl group of glutamyl residues. This modification, present in one of the most stable microtubular systems, may influence microtubule stability or axoneme function, or both.

Class I and IVa beta-tubulin isotypes expressed in adult mouse brain are glutamylated

Several types of post-translational modifications contribute to the high level of tubulin heterogeneity in the brain. An important modification is glutamylation of the major brain-specific isotypes, such as class Ia/b of alpha-tubulin and classes II and III of beta-tubulin. Here we describe experiments to determine if additional, minor tubulin isotypes, expressed in adult mouse brain, could also be glutamylated. Purified tubulin from adult mouse brain was cleaved with thermolysin. Proteolytically released carboxy-terminal peptides of both alpha- and beta-tubulin were isolated by sequential anion exchange and reverse-phase column-chromatography. Anionic peptides were then characterized by amino acid sequencing and mass spectrometry. We show that brain-specific class IVa and constitutive class I beta-tubulin isotypes can be glutamylated, at Glu434 and Glu441, respectively.

Evidence for a conformational polymorphism of invertebrate neurohormones. D-amino acid residue in crustacean hyperglycemic peptides

Several large peptidic neurohormones have been isolated in crustaceans. In lobster and other related species, each of these neurohormones, and particularly the crustacean hyperglycemic hormone, occurs as two isoforms having the same peptidic sequence and molecular mass. We report here that these isoforms differ by the configuration of a single amino acid residue. The third residue (Phe3) of the lobster hyperglycemic hormones is in either the L- or D-configuration. In addition, we have shown that the biological activity of the two isoforms differs when considering the kinetics of their hyperglycemic effect.

Purification and biological activity of a recombinant human erythropoietin produced by lymphoblastoid cells

A recombinant human erythropoietin (rH-EPO) was obtained from the culture supernatants of human B-lymphoblastoid cells transfected by the human EPO gene. rH-EPO was purified by a two-step method based on immunoaffinity and ion exchange chromatography. The first step was achieved by an anti-EPO monoclonal antibody (Mab). This Mab, immobilized on Sepharose 4B, allowed a 410-fold purification of the protein. The second step consisted of ion exchange chromatography on DEAE Sephacel. The combination of these two steps results in a highly purified rH-EPO with a global yield of about 50%; the specific activity of the protein was 176,000 IU/A280. The NMR spectrum was characteristic for a well structured, single-conformation protein. The purified protein was analyzed by SDS-PAGE and isoelectric focusing. The biological activity of purified rH-EPO was measured in vivo, by the incorporation of 59Fe into red blood cells (RBC) of polycythemic mice and in vitro by the proliferative response of an EPO-dependent cell line. The purified protein expressed in lymphoblastoid cells of human origin had the same biological activity as that of urinary EPO and rH-EPO produced in other mammalian cells.

Protein processing and morphogenesis of secretory granules in Paramecium

The ciliated protozoan Paramecium provides a model system for the study of regulated secretion, featuring architecturally complex secretory storage granules-trichocysts-docked at the plasma membrane, ready to respond to an exocytotic stimulus. The trichocysts are characterized by crystalline contents that confer upon the organelle a defined shape which can be altered by single gene mutation. The crystalline trichocyst contents are built up from a heterogeneous set of small acidic polypeptides generated by proteolytic maturation of a family of precursor molecules, suggesting an important role for protein processing in this system. We have recently shown that the primary defect in several secretory mutants lacking functional trichocysts is in intracellular trafficking rather than protein processing. However, analysis of how these defects lead to altered trichocyst shape supports the notion that the protein processing is essential for morphogenesis. Preliminary results of a cloning project reveal that an extensive multigene family (approximately 100 genes) codes for the trichocyst matrix proteins. Deduced amino acid sequences of putative processing sites indicate that (at least) two distinct processing reactions are probably involved in the maturation of these proteins, and allow us to speculate that each reaction may control a key event of trichocyst biogenesis.

Four 9-kDa proteins excreted by somatic embryos of grapevine are isoforms of lipid-transfer proteins

Four 9-kDa small extracellular proteins produced by embryogenic cultures in the absence of auxin have been purified from the extracellular medium of grapevine somatic embryo cultures through cation-exchange chromatography and hydrophobic-interaction chromatography. The partial amino-acid sequences reflect high similarities between the four proteins as well as with the sequences established for carrot, spinach, millet and maize nonspecific lipid-transfer proteins. All these sequences show conservation of three cysteines at positions 4, 14 and 30-32, as well as glycine, valine, tyrosine and lysine residues at positions 5, 7, 17 and 37, respectively. In-vitro lipid-transfer assays reveal that the four proteins catalyze the transfer of phosphatidylcholine from liposomes towards mitochondria with an efficiency similar or higher than that of a purified maize lipid-transfer protein.

Electrospray ionization mass spectrometry on hydrophobic peptides electroeluted from sodium dodecyl sulfate-polyacrylamide gel electrophoresis application to the topology of the sarcoplasmic reticulum Ca2+ ATPase

We describe a method to prepare proteins and peptides in a state suitable for exact determination of molecular mass by electrospray ionization mass spectrometry after sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution. The utility of the procedure, in conjunction with N-terminal sequencing, in defining the C-terminal end of the peptide fragments produced by proteolysis of sarcoplasmic reticulum Ca2+ ATPase with V8 is demonstrated. The application of mass spectrometry aids significantly the use of proteolytic enzymes for topological studies of membrane proteins, and SDS-PAGE is preferable to reverse-phase HPLC for separation of membraneous, hydrophobic peptides and proteins.

Frog prodermorphin expressed in mammalian cells is partly converted to the hydroxyproline containing precursor

Using recombinant vaccinia virus, we have expressed in mammalian cells the cDNA coding for the precursor of dermorphin, a D-alanine containing opioid peptide from the skin of the South American frog Phyllomedusa sauvagei. HeLa cells and AtT-20 cells produced prodermorphin where proline-6 of dermorphin was partly hydroxylated. This was demonstrated by digesting the partially purified precursors with trypsin and carboxypeptidase B. After immunoprecipitation and separation by HPLC, two decapeptides were detected which differed by the presence of proline or hydroxy-proline at position 6. This demonstrates that HeLa cells as well as AtT-20 cells can perform the post-translational conversion of certain proline residues to hydroxyproline in a foreign hormone precursor expressed in these cells.

Photo-cross-linking of CRP to nonspecific DNA in the absence of cAMP. DNA interacts with both the N- and C-terminal parts of the protein

Adenosine cyclic 3',5'-phosphate receptor protein (CRP or CAP) is a regulatory protein involved in the transcription of several operons in Escherichia coli. cAMP-independent, nonspecific complexes of CRP and DNA were investigated by photochemical cross-linking of the protein to nonspecific DNA, whose thymines are substituted by 5-bromouracil (BrUra). The cross-linked protein was completely digested by trypsin, and the covalently bound peptides were sequenced. We identified two regions of the protein in close contact with DNA: one in the C-terminal part, overlapping the canonical helix-turn-helix motif, and the other one in the N-terminal part, which is usually not considered to belong to the DNA-interacting domain of CRP. This result lead us to propose models for nonspecific interaction, where the DNA is in contact with both the N- and C-terminal parts of the protein.

The asiA gene of bacteriophage T4 codes for the anti-sigma 70 protein

The anti-sigma 70 factor of bacteriophage T4 is a 10-kDa (10K) protein which inhibits the sigma 70-directed initiation of transcription by Escherichia coli RNA polymerase holoenzyme. We have partially purified the anti-sigma 70 factor and obtained the sequence of a C-terminal peptide of this protein. Using reverse genetics, we have identified, at the end of the lysis gene t and downstream of an as yet unassigned phage T4 early promoter, an open reading frame encoding a 90-amino-acid protein with a predicted molecular weight of 10,590. This protein has been overproduced in a phage T7 expression system and partially purified. It shows a strong inhibitory activity towards sigma 70-directed transcription (by RNA polymerase holoenzyme), whereas it has no significant effect on sigma 70-independent transcription (by RNA polymerase core enzyme). At high ionic strength, this inhibition is fully antagonized by the neutral detergent Triton X-100. Our results corroborate the initial observations on the properties of the phage T4 10K anti-sigma 70 factor, and we therefore propose that the gene which we call asiA, identified in the present study, corresponds to the gene encoding this T4 transcriptional inhibitor.

BEN, a surface glycoprotein of the immunoglobulin superfamily, is expressed in a variety of developing systems

We have previously identified a 95- to 100-kDa cell surface glycoprotein, which we named BEN (for bursal epithelium and neurons), that is widely expressed during chicken embryonic development. In the central nervous system, it is restricted to subsets of neurons including the motoneurons and the inferior olivary nucleus neurons (which provide the cerebellum with the climbing fibers) where its expression occurs during the phase of axonogenesis and synaptogenesis. In the present work, we show that BEN expression extends to a variety of tissues originating from the three embryonic germ layers. We have found that BEN immunopurified from neural, epithelial, and hemopoietic tissues is differently glycosylated and may or may not carry the HNK-1 epitope. We then cloned a full-length cDNA encoding this protein. Analysis of its sequence reveals that BEN is a member of the immunoglobulin superfamily. Two molecules with an identical cDNA sequence were recently reported: DM-GRASP [Burns, F. R., Von Kannen, S., Guy, L., Raper, J. A., Kamholz, J. & Chang, S. (1991) Neuron 7, 209-220] and SC1 [Tanaka, H., Matsui, T., Agata, A., Tomura, M., Kubota, I., Mcfarland, K. C., Kohr, B., Lee, A., Phillips, H. S. & Shelton, D. L. (1991) Neuron 7, 535-545]. Their pattern of expression and structural properties are consistent with those reported for BEN. Therefore BEN, DM-GRASP, and SC1 are likely to be the same molecule of the immunoglobulin superfamily.

Structure of the polyglutamyl side chain posttranslationally added to alpha-tubulin

Polyglutamylation, a new posttranslational modification of tubulin identified originally on the acidic alpha variants by Eddé et al. (Eddé, B., Rossier, J., Le Caer, J. P., Desbruyeres, E., Gros, F., and Denoulet, P. (1990) Science 247, 83-85), consists of the successive addition of glutamyl units to the Glu445. To characterize their linkage mode mouse tubulin was posttranslationally labeled with [3H]glutamate. After digestion of [3H]tubulin with thermolysin, up to eight radioactive peaks were separated on an anion exchange column (DEAE). Combined use of Edman degradation sequencing and mass spectrometry analysis of the first 6 one indicated that they all correspond to the same COOH-terminal sequence 440VEGEGEEEGEE450 bearing one to six glutamyl units on the Glu445. The first glutamyl residue is amide-linked to the gamma-carboxyl group of Glu445, but the additional residues can be linked to the gamma- or alpha-carboxyl groups of the preceding one. All possible linkages for the biglutamylated tubulin peptides (gamma 1 alpha 2, gamma 1 gamma 2) and triglutamylated (gamma 1 alpha 2 alpha 3, gamma 1 alpha 2 gamma 3, gamma 1 alpha 2 gamma 2, gamma 1 gamma 2 alpha 3, gamma 1 gamma 2 gamma 3) were synthesized. These different peptides were successfully separated on a C18 5-micron reverse phase column. We found that the bi- and triglutamylated tubulin peptides behave as the gamma 1 alpha 2 and gamma 1 alpha 2 alpha 3 synthetic peptides, respectively. These results indicate that the second and third glutamyl residues of the polyglutamyl side chain are amide-linked to the alpha-carboxyl group of the preceding unit.

Characterization of a major brain tubulin variant which cannot be tyrosinated

Brain tubulin preparations contain an abundant type of tubulin which does not undergo the normal cycle of tyrosination-detyrosination, and whose nature is still unknown. We have used peptide sequence analysis and mass spectrometry combined with immunological procedures to show that this non-tyrosinatable tubulin has a specific primary structure. It differs from the tyrosinated isotype in that it lacks a carboxy-terminal glutamyl-tyrosine group on its alpha-subunit. Thus, non-tyrosinatable tubulin originates from a well-defined posttranslational modification of the tubulin primary structure which is located at the expected site of activity of tubulin tyrosine ligase. This probably accounts for the reason why it cannot be tyrosinated. The significance of this abundant brain isotubulin and the metabolic pathway involved in its formation remain to be elucidated. This should shed light on the relation between the structural diversity of the carboxy terminus of alpha-tubulin and the regulation of functional properties of microtubules.

Phosphorylation of human recombinant tyrosine hydroxylase isoforms 1 and 2: an additional phosphorylated residue in isoform 2, generated through alternative splicing

The single human tyrosine hydroxylase (TH) gene generates four different mRNA species through alternative splicing events. TH-1 and TH-2 mRNAs are expressed mostly in the brain. We have produced large amounts of the corresponding proteins in Escherichia coli to analyze their respective molecular characteristics. The polypeptides have molecular weights similar to those of TH expressed in Xenopus oocytes and react with antibodies to TH. The two isoforms were purified with a purity of 90% using a three-step procedure. The phosphorylation sites have been determined in the two isoforms after labeling with [gamma-32P]ATP in the presence of cAMP-dependent protein kinase (PKA) or calmodulin-dependent protein kinase II (CaM-PK II). In both isoforms, Ser-40 was found to be phosphorylated by PKA, and Ser-19 and Ser-40 were found to be phosphorylated by CaM-PK II. The putative phosphorylation site generated by alternative splicing (Ser-31) was phosphorylated specifically by CaM-PK II in TH-2 only. The kinetic properties of the two isoforms in the presence of various concentrations of the substrate (tyrosine) and of the natural cofactor [6R)-tetrahydrobiopterin) were also analyzed. TH produced in E. coli is unphosphorylated but nevertheless active. At 50 microM tyrosine and 300 microM (6R)-tetrahydrobiopterin, the specific activities of TH-1 and TH-2 are 1300 and 620 nmol of dihydroxyphenylalanine/min/mg, respectively. Phosphorylation of TH-1 and TH-2 by PKA activates both isoenzymes as shown by the increase in the affinity for the cofactor. No changes in kinetic parameters of the isoenzymes were observed after phosphorylation by CaM-PK II. Dopamine was found to inhibit both TH isoenzymes to the same extent as shown by their similar Ki values for dopamine. These values were increased after phosphorylation of each enzyme by PKA. Unlike TH-1, phosphorylation of TH-2 by CaM-PK II resulted in an increase of the Ki value for dopamine. This property may be related to the presence of the additional phosphorylated residue in TH-2 isoform.

Primary structure of two isoforms of the vitellogenesis inhibiting hormone from the lobster Homarus americanus

The amino acid sequence of two isoforms of the Vitellogenesis Inhibiting Hormone from the lobster Homarus americanus (one biologically active and one inactive in a heterologous bioassay) has been established by gas-phase microsequencing and fast-atom bombardment mass spectrometry. These two isoforms, isolated from sinus glands display the same sequence of 77 amino acid residues (m.w.: 9135 Da) and have a free N-terminus. Structurally related to Crustacean Hyperglycemic Hormone and Molt Inhibiting Hormone, the Vitellogenesis Inhibiting Hormone of the lobster clearly appears as an original member of the newly described family of neuropeptides, so far proper to crustaceans, which are involved in the control of major physiological functions.

A combination of posttranslational modifications is responsible for the production of neuronal alpha-tubulin heterogeneity

We describe the presence of alpha-tubulin and MAP2 acetyltransferase activities in mouse brain. The enzyme(s) copurified with microtubules through two cycles of assembly-disassembly. Incubation of microtubule proteins with [3H]acetyl CoA resulted in a strong labeling of both alpha-tubulin and MAP2. To determine the site of the modification, tubulin was purified and digested with Glu-C endoproteinase. A unique radioactive peptide was detected and purified by HPLC. Edman degradation sequencing showed that this peptide contained epsilon N-acetyllysine at position 40 of the alpha-tubulin molecule. This result demonstrates that mouse brain alpha-tubulin was acetylated at the same site as in Chlamydomonas. Isoelectric focusing analysis showed that acetylated alpha-tubulin was resolved into five isoelectric variants, denoted alpha 3 and alpha 5 to alpha 8. This heterogeneity is not due to acetylation of other sites but results from a single acetylation of Lys40 of an heterogeneous population of alpha-tubulin isoforms. These isoforms are produced by posttranslational addition of one to five glutamyl units. Thus, neuronal alpha-tubulin is extensively modified by a combination of modifications including acetylation, glutamylation, tyrosylation, and other yet unknown modifications.

Molecular cloning of RI-HB, a heparin binding protein regulated by retinoic acid

RI-HB is an extracellular heparin binding protein regulated by retinoic acid and essentially expressed during embryogenesis. This study reports the cloning and sequencing of the cDNA that encodes RI-HB. The sequence of RI-HB contains 121 amino acid residues and is very rich in basic amino acids and cysteines. This sequence was compared to those of HBGAM and MK protein, two other heparin binding proteins exhibiting growth and/or neurotrophic activities. Northern blot analysis indicates that RI-HB mRNA is strongly expressed during early chicken embryogenesis and that it is induced by retinoic acid treatment of chicken fibroblasts and myotubes in culture.