Hydrolysis of the bovine insulin B-chain in bidistilled modified water

It was shown that bidistilled modified water substantially enhances the hydrolysis of the peptide the bovine insulin B-chain. The exposure of the peptide to bidistilled modified water for 20 hours at room temperature leads to an almost complete hydrolysis of its molecule into fragments that differ from the initial molecule in elution time from a column in high-performance liquid chromatography.     

多肽内切酶鉴定牙龈卟啉单胞菌血凝素2结合位点

目的利用多肽内切酶分析牙龈卟啉单胞菌凝血素2(Porphyromonas gingivalishemagglutinin-2,PgHA-2)与氯化血红素结合位点的氨基酸序列。方法Endoproteinase Lys-C多肽内切酶水解获得与氯化血红素结合的功能性的多肽片段,质谱技术鉴定多肽片段的氨基酸序列。结果质谱鉴定与氯化血红素结合的多肽片段的氨基酸序列为YAVNDGFPGDHYAVMISK。结论进一步明确了HA-2与氯化血红素结合位点的氨基酸序列,为牙周病的预防和治疗方法的改进奠定基础。     

Effect of limited proteolysis in the 8th loop of the barrel and of antibodies on porcine pancreas amylase activity.

The porcine pancreatic alpha-amylase is a (beta/alpha)8-barrel protein, containing domains A and B (peptide sequence 1-403) and a distinct C-domain (peptide sequence 404-496). Separation of the terminal C-domain from the A and B domains has been attempted by limited proteolysis in the hinge region. Subtilisin was found to hydrolyse amylase between residues 369 and 370 situated in the loop between the eighth beta-strand and alpha-helix. The cleaved amylase was isolated by chromatofocusing and found to retain about 60% of the activity of the native enzyme, while the isolated fragments were inactive. Antigen binding fragments prepared from polyclonal antibodies to native amylase and the CNBr-fragment P1 (peptide sequence 395-496) respectively, were tested for influence on the enzyme activity. Antibodies directed against P1 had no effect whereas antibodies against the peptide sequence 1-394 and amylase respectively inhibited hydrolysis of substrates having four or more glucose residues but not of shorter oligomaltosides. Crystallographic analysis revealed that changes in the region of residue 369 might affect the conformation of the active site as well as of a second binding site. This site, located on the enzyme surface, is proposed to be required for the hydrolysis of larger substrates.     

Identification of insulin intermediates and sites of cleavage of native insulin by insulin protease from human fibroblasts

We have studied the time sequence degradation of native insulin by insulin protease from human fibroblast using multiple steps involving purification of the products by high performance liquid chromatography, determination of peak composition by amino acid sequence analysis, and confirmation of structure by mass spectrometry and thus elucidated the sites of cleavage of insulin by human insulin protease. We observed that as early as 0.5 min of incubation, three major new peptide peaks, intact insulin, and four smaller peptide peaks can be detected. The major peptides are portions of the insulin molecule, with the amino ends of the A and B chains or the carboxyl ends of the A and B chains still connected by disulfide bonds. Peptide peak I is A1-13-B1-9. Peptide peak II is A1-14-B1-9. Peptide peak III is A14-21-B14-30. The smaller peptide peaks are A14-21-B17-30, A15-21-B14-30, A15-21-B10-30, and A14-21-B10-30. The major peptide bond cleavage sites therefore consist of A13-14, A14-15, B9-10, B13-14, and B10-17. With longer incubation times, peptide peak II appears to lose the A14 tyrosine to form peptide peak I. This peptide I, which is the amino end of the A and B chains, is not further degraded even after 1.5 h of incubation. With longer incubation times, the peptides containing the carboxyl ends of the A and B chains are further degraded to form products from cleavage at the A18-19, B14-15, B25-26, and a small amount of A19-20, B10-11, and B24-25 cleavage and the emergence of 2-5-amino acid peptide chains, tyrosine, alanine, histidine, and leucine-tyrosine. We conclude, based on the three-dimensional structure of insulin, that human insulin protease recognizes the alpha-helical regions around leucine-tyrosine bonds and that final degradation steps to small peptides do not require lysosomal involvement.     

Threonine 1336 of the human insulin receptor is a major target for phosphorylation by protein kinase C

The ability of tumor-promoting phorbol diesters to inhibit both insulin receptor tyrosine kinase activity and its intracellular signaling correlates with the phosphorylation of the insulin receptor beta subunit on serine and threonine residues. In the present studies, mouse 3T3 fibroblasts transfected with a human insulin receptor cDNA and expressing greater than one million of these receptors per cell were labeled with [32P]phosphate and treated with or without 100 nM 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA). Phosphorylated insulin receptors were immunoprecipitated and digested with trypsin. Alternatively, insulin receptors affinity purified from human term placenta were phosphorylated by protein kinase C prior to trypsin digestion of the 32P-labeled beta subunit. Analysis of the tryptic phosphopeptides from both the in vivo and in vitro labeled receptors by reversed-phase HPLC and two-dimensional thin-layer separation revealed that PMA and protein kinase C enhanced the phosphorylation of a peptide with identical chromatographic properties. Partial hydrolysis and radiosequence analysis of the phosphopeptide derived from insulin receptor phosphorylated by protein kinase C indicated that the phosphorylation of this tryptic peptide occurred specifically on a threonine, three amino acids from the amino terminus of the tryptic fragment. Comparison of these data with the known, deduced receptor sequence suggested that the receptor-derived tryptic phosphopeptide might be Ile-Leu-Thr(P)-Leu-Pro-Arg. Comigration of a phosphorylated synthetic peptide containing this sequence with the receptor-derived phosphopeptide confirmed the identity of the tryptic fragment. The phosphorylation site corresponds to threonine 1336 in the human insulin receptor beta subunit.(ABSTRACT TRUNCATED AT 250 WORDS)     

A novel peptide, pyroglutamylglutamylproline amide, in the rabbit prostate complex, structurally related to thyrotrophin-releasing hormone

A novel peptide which cross-reacts with an antibody to thyrotrophin-releasing hormone has been isolated and characterized from the rabbit prostate complex. The peptide exhibited an amino acid composition of Glx1.7, Pro1.0, and automatic gas phase sequence analysis after mild acid hydrolysis established the sequence Glu-Glu-Pro. Fast atom bombardment mass spectrometry gave a pseudomolecular ion (M + H)+ of 355.2 confirming that the prostate peptide has the structure of pGlu-Glu-Pro-NH2. This peptide differs from authentic thyrotrophin-releasing hormone by the substitution of glutamic acid for histidine at position 2.     

Permeation and stereospecificity of hydrolysis of peptide esters within intact lysosomes in vitro

Various dialanine ethyl esters and di- and trimethionine methyl ester diastereomers have been shown to bring about, at a concentration range of 0.5 5mM, the loss of latency of rat liver by lysosomal acid phosphatase. Concurrently an examination was made of the hydrolysis of the peptide esters by a lysosomal enzyme composite.The total hydrolysis of peptide esters involves several steps. Using a variety of siastereomers it was possible to elucidate the stereospecificity of the enzymes involved, i.e. an ester bond involving a D-amino acid residue as well as peptide bonds involving either a DD or a DL configuration in the amino terminal end and an LD configuration in a sequence of DLD are not susceptible to enzymic hydrolysis.A correlation was found between the potency of a given peptide ester in damaging lysosomal integrity and its susceptibility to hydrolysis by the lysosomal enzyme composite. It is suggested that lysosomal rupture stems from intralysosomal peptide ester hydrolysis, leading to an accumulation of zwitteron degradation products. The broad stereospecificity of the permeating species and the discrimination between trialanine and trimethionine esters lead to the suggestion that the permeation involves partition between the medium and the non-polar regions of the lysosomal membrane.     

Chromosome-encoded beta-lactamases of Citrobacter diversus. Interaction with beta-iodopenicillanate and labelling of the active site.

Both forms of the chromosome-encoded beta-lactamase of Citrobacter diversus react with beta-iodopenicillanate at a rate characteristic of class A beta-lactamases. The active site of form I was labelled with the same reagent. The sequence of the peptide obtained after trypsin hydrolysis is identical with that of a peptide obtained in a similar manner from the chromosome-encoded beta-lactamase of Klebsiella pneumoniae.     

Phosphorylation of synthetic insulin receptor peptides by the insulin receptor kinase and evidence that the preferred sequence containing Tyr-1150 is phosphorylated in vivo

Three peptides were synthesized corresponding to potential autophosphorylation sites of the beta subunit of the human insulin receptor. These were peptide 1150 corresponding to amino acids 1142-1153 of the pro-receptor, peptide 960 corresponding to amino acids 952-961 of the proreceptor, and peptide 1316 corresponding to amino acids 1313-1329 of the proreceptor. Peptide 1150 served as a better substrate for the insulin receptor tyrosine protein kinase than either of the other peptides or than the Src peptide (corresponding to the sequence surrounding the autophosphorylation site at Tyr-416). Microsequencing of the phosphorylated peptide 1150 indicated that Tyr-1150 rather than Tyr-1146 or Tyr-1151 was phosphorylated in the in vitro reaction. The insulin receptor was then isolated from 32P-labeled IM-9 cells that had been exposed to insulin. Tryptic digestion of the beta subunit revealed one peptide whose phosphorylation was dependent upon insulin and occurred exclusively on Tyr. This peptide was selectively immunoprecipitated by an antipeptide antibody directed to the Tyr-1150-containing sequence. We conclude that Tyr-1150 is preferentially phosphorylated by the purified receptor kinase and that one of the autophosphorylation reactions elicited by insulin in intact cells occurs in a sequence that contains this residue.     

Structural effect of a recombinant monoclonal antibody on hinge region peptide bond hydrolysis

IgG hinge region peptide bonds are susceptible to degradation by hydrolysis. To study the effect of Fab and Fc on hinge region peptide bond hydrolysis, a recombinant humanized monoclonal IgG1 antibody, its F(ab')2 fragment, and a model peptide with amino acid sequence corresponding to the hinge region were incubated at 40 degrees C in formulation buffer including complete protease inhibitor and EDTA for 0, 2, 4, 6 and 8 weeks. Two major cleavage sites were identified in the hinge region of the intact recombinant humanized monoclonal antibody and its F(ab')2 fragment, but only one major cleavage site of the model peptide was identified. Hinge region peptide bond hydrolysis of the intact antibody and its F(ab')2 fragment degraded at comparable rates, while the model peptide degraded much faster. It was concluded that Fab region of the IgG, but not Fc portion had significant effect on preventing peptide bond cleavage by direct hydrolysis. Hydrolysis of hinge region peptide bonds was accelerated under both acidic and basic conditions.     

Identification of phospholipase C-gamma1 as a mitogen-activated protein kinase substrate

The discovery of sequence motifs that mediate protein-protein interactions, coupled with the availability of protein amino acid sequence data, allows for the identification of putative protein binding pairs. The present studies were based on our identification of an amino acid sequence in phosphatidylinositol-specific phospholipase C-gamma1 (PLC-gamma1) that fits the consensus sequence for a mitogen-activated protein kinase (MAPK) binding site, termed the D-domain. Extracellular signal-regulated kinase 2 (ERK2), an MAPK, and phospho-ERK2 were bound by an immobilized peptide sequence containing the identified PLC-gamma1 D-domain. Furthermore, a peptide containing the PLC-gamma1 D-domain was able to competitively inhibit the in vitro phosphorylation of recombinant PLC-gamma1 by recombinant phospho-ERK2, whereas a control peptide derived from a distant region of PLC-gamma1 was ineffective. Similarly, the peptide containing the PLC-gamma1 D-domain, but not the control peptide, competitively inhibited the in vitro phosphorylation of Elk-1 and c-Jun catalyzed by recombinant phospho-ERK2 and phospho-c-Jun N-terminal kinase 3 (phospho-JNK3), another type of MAPK, respectively. Incubation of anti-PLC-gamma1 immunocomplexes isolated from rat brain with recombinant phospho-ERK2 opposed the increase in PLC-gamma1-catalyzed hydrolysis of phosphatidylinositol 4,5-P(2) (PtdIns(4,5)P(2)), which was produced by a tyrosine kinase associated with the immunocomplexes, whereas in vitro phosphorylation of recombinant PLC-gamma1 by recombinant phospho-ERK2 did not alter PLC-gamma1-catalyzed PtdIns(4,5)P(2) hydrolysis. These studies have uncovered a previously unidentified mechanism for the integration of PLC-gamma1- and ERK2-dependent signaling.     

Phosphorylation of Xenopus elongation factor-1 gamma by cdc2 protein kinase: identification of the phosphorylation site.

The cdc2 protein kinase phosphorylates elongation factor-1 gamma (EF-1 gamma) during meiotic maturation of Xenopus oocytes. A synthetic peptide P2: PKKETPKKEKPA matching the cDNA-deduced sequence of EF-1 gamma was an in vitro substrate for cdc2 protein kinase and inhibited phosphorylation of EF-1 gamma. Tryptic hydrolysis of EF-1 gamma and the P2 peptide, both phosphorylated by cdc2 protein kinase, resulted in multiple partial digestion products generated by the presence of barely hydrolysable bonds. The two peptides obtained from the hydrolysis of EF-1 gamma comigrated exactly in two-dimensional separation with two of the P2 peptide hydrolysates. EF-1 gamma therefore contains one unique phosphoacceptor for cdc2 protein kinase, identified as threonine-230.     

Sequence determination by MALDI-TOF mass spectrometry of an insecticidal lentil peptide of the PA1b type

Mature seeds of lentil (Lens culinaris Medik.) were previously reported to contain an insecticidal cysteine-rich peptide, likely of the albumin-1 subunit b type. The purpose of this work was to determine the amino acid sequence of this insecticidal lentil peptide in an Eston lentil extract by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), after reduction of the disulfide bridges, alkylation of the cysteine residues and hydrolysis by pronase, trypsin, chymotrypsin and endoproteinase Asp-N. Sequences of key fragments were supported by monoisotopic mass measurements and by sequence ions from collision-induced dissociation (CID) experiments with a MALDI-TOF/TOF analyzer (MS/MS analysis). The new 37 amino acid sequence revealed strong similarities to a histidine-containing pea PA1b peptide and to soybean leginsulins but with a unique segment of RSSA in the middle. The lentil PA1b peptide sequence agreed completely with that derived from a L. culinaris genomic DNA sequence.     

Glycine flanked by hydrophobic bulky amino acid residues as minimal sequence for effective subtilisin catalysis.

The specificity of alkaline mesentericopeptidase (a proteinase closely related to subtilisin BPN') for the C-terminal moiety of the peptide substrate (Pi' specificity) has been studied in both hydrolysis and aminolysis reactions. N-Anthraniloylated peptide p-nitroanilides as fluorogenic substrates and amino acid or peptide derivatives as nucleophiles were used in the enzymic peptide hydrolysis and synthesis. Both hydrolysis and aminolysis kinetic data suggest a stringent specificity of mesentericopeptidase and related subtilisins to glycine as P1' residue and predilection for bulky hydrophobic P2' residues. A synergism in the action of S1' and S2'subsites has been observed. It appears that glycine flanked on both sides by hydrophobic bulky amino acid residues is the minimal amino acid sequence for an effective subtilisin catalysis.     

The amino acid sequence of an active site peptide from the H,K-ATPase of gastric mucosa

The gastric H,K-ATPase is an active transport protein that is responsible for the maintenance of a large pH gradient across the secretory canaliculus of the mammalian parietal cell. Acid secretion across these epithelial cell membranes is coupled to the potassium-stimulated hydrolysis of ATP catalyzed by H,K-ATPase, but the mechanism of coupling between ion transport and ATP hydrolysis is unknown. In order to investigate the enzymatic mechanism of this coupling, a peptide derived from the ATP binding site of H,K-ATPase has been purified and its amino acid sequence has been determined. The peptide was identified by the incorporation of a fluorescent probe, fluorescein 5'-isothiocyanate (FITC), into the active site before trypsin digestion of the protein. The labeling of the enzyme by FITC was associated with the irreversible inhibition of enzymatic activity, and both the labeling of the tryptic peptide and inhibition of activity were prevented when the reaction was performed in the presence of ATP. At 100% inhibition of activity, 3.5 +/- 1.6 nmol of FITC were incorporated per mg of protein. The amino acid sequence of the active site peptide is His-Val-Leu-Val-Met-Lys-Gly-Ala-Pro-Glu-Gln-Leu-Ser-Ile-Arg, and FITC reacts with the lysine. This sequence is very similar to sequences of fluorescein-labeled peptides from the ATP binding sites of Na,K-ATPase and Ca2+-ATPase, and suggests that the active site structures of these ion transport ATPases are similar.     

Primary structure of cytoplasmic aspartate aminotransferase from pig heart muscle. Amino acid sequence of peptides from cyanogen bromide hydrolysate]

Amino acid sequences were determined for the six peptides from cyanogen bromide hydrolysis of cytoplasmic aspartate aminotransferase. These peptides accounted for 177 amino acid residues of the enzyme. Partial sequence of N-terminal peptide accounting for 212 amino acid residues of enzyme was also determined.     

Purification of a novel nitric oxide inhibitory peptide derived from enzymatic hydrolysates of Mytilus coruscus

Shellfish contain significant levels of high quality protein and are therefore a potential source for biofunctional high-value peptides. To purify a novel anti-inflammatory peptide from Mytilus coruscus (M. coruscus), we applied enzymatic hydrolysis and tangential flow filtration (TFF) and investigated its nitric oxide inhibitory property. To prepare the peptide, eight proteases were employed for enzymatic hydrolysis. Flavouzyme hydrolysates, which showed clearly superior nitric oxide inhibitory activity on lipopolysaccharide (LPS)-stimulated RAW264.7, were further purified using a TFF system and consecutive chromatographic methods. Finally, a novel anti-inflammatory peptide composed of 10 amino acid residues was obtained, and the sequence was identified as Gly-Val-Ser-Leu-Leu-Gln-Gln-Phe-Phe-Leu at N-terminal position. The peptide from M. coruscus effectively inhibited nitric oxide production on macrophage cells. This is the first report of an anti-inflammatory peptide derived from the hydrolysates of M. coruscus.     

Cellular processing of pre-proparathyroid hormone involves rapid hydrolysis of the leader sequence.

The cellular synthesis of parathyroid hormone (PTH) involves two consecutive cleavages of NH2-terminal peptide sequences from a larger precursor, pre-proparathyroid hormone (Pre-ProPTH). The initial cleavage consists of the removal of an NH2-terminal leader sequence either during or shortly after biosynthesis of the polypeptide chain is complete. To determine the fate of the cleaved leader sequence, we prepared, by chemical synthesis, a peptide based on the known structure of the leader sequence of pre-proparathyroid hormone and used this peptide labeled with 125iodine as a marker to monitor the recovery of the putative cellular leader peptide during extraction and electrophoresis of [35S]methionine-labeled proteins from pulse-labeled parathyroid gland slices. Under conditions in which the recovery of the synthetic leader peptide was 50 to 70%, we found no detectable 35S-labeled product in the region of sodium dodecyl sulfate gels where the synthetic peptide migrates. In view of the known methionine content of pre-proparathyroid hormone and proparathyroid hormone (ProPTH), it would have been possible to detect endogenously labeled leader peptide if present in amounts equal to 0.05% of the amount of labeled ProPTH present in the tissues. These observations indicate that the cellular conversion of Pre-ProPTH to ProPTH involves a rapid hydrolysis of the leader peptide either during or immediately after its removal from the precursor.     

The amino acid sequences of the tryptic peptides of cowpea chlorotic mottle virus protein

The amino acid sequences of the major tryptic peptides from the coat protein of wild type cowpea chlorotic mottle virus are presented. The sequences have been determined by a combination of enzyme hydrolysis, mass spectrometry and Edman degradation, and the relative usefulness of mass spectrometry in this peptide sequence determination is discussed.     

Determination of the amino acid sequence in a cyclic lipopeptide using MS with DHT mechanism

A TOF MS/MS method to directly determine the amino acid sequence in a cyclic lipopeptide without its hydrolysis is described. The fragments of the peptide and the hydrocarbon chains were identified through comparing the MS of two analogues of the lipopeptide; the connecting relationship of amino acid residues in the lipopeptide was determined based on the difference of mass to charge ratio between peaks in the MS spectra and the amino acid analysis; and finally, according to the mechanism of double hydrogen transfer(DHT) the C-terminal of peptide and hydroxy aliphatic acid in the lipopeptide was directly determined without the hydrolysis. The determined sequence of amino acid residues in the cyclic lipopeptide is also supported by the rest peaks in the MS spectra grounded on simple fragmenting mechanism. This method can be used to determine the amino acid sequence in any aliphatic acid loop-inlaying cyclic lipopeptides.