Goat immunoglobin G. Peptide chains and terminal residues

Goat immunoglobulin G (IgG) was isolated and characterized. The molecular weights of the IgG and its heavy chains and light chains were found to be 144000, 53600 and 23000 respectively. The light chain corresponds to human L type as was shown by the absence of C-terminal S-carboxymethylcysteine and its high content of N-terminal pyrrolid-2-one-5-carboxylic acid (PCA). The major C-terminal residue of the light chain was serine and the major N-terminal dipeptide was PCA-Ala (0.6mole/mole). The major C-terminal residue of the heavy chain was glycine and the N-terminal sequence of the heavy chain is PCA-Val-Gln. This tripeptide was obtained in a 70% yield.     

Glutamine as a precursor to N-terminal pyrrolid-2-one-5-carboxylic acid in mouse immunoglobulin λ-type light chains. Amino acid-sequence variability at the N-terminal extra piece of λ-type light-chain precursors

The mRNA molecules coding for three mouse immunoglobulin lambda-type light (L) chains (MOPC-104E lambda(1), RPC-20 lambda(1), MOPC-315 lambda(2)) programme the cell-free synthesis of precursors larger than the mature proteins. Radioactive amino acid-sequence analyses of each of the three precursors labelled with [(3)H]alanine, [(3)H]serine, [(3)H]glutamine, [(3)H]glutamic acid and [(3)H]threonine showed that an extra piece, at least 18 residues long, is linked to the N-terminus of the mature L-chains. The N-terminal extra-peptide segment may be 19 residues long, since analyses of precursors labelled with [(35)S]methionine indicated an additional N-terminal methionine residue which was recovered in low yields. Presumably this is the initiator methionine, which is known to be short lived in eukaryotes. The mature forms of MOPC-104E, RPC-20 and MOPC-315 lambda L-chains are blocked at the N-termini by pyrrolid-2-one-5-carboxylic acid (pyroglutamic acid). Sequence analyses of precursors labelled with [(3)H]glutamine and [(3)H]glutamic acid showed incorporation only of glutamine in a position that matches with the position of pyrrolid-2-one-5-carboxylic acid in the mature forms of all three precursors, and incorporation of glutamic acid in other positions. The data showed the absence of glutamine-glutamic acid interconversion, since the radioactive peaks obtained from either (3)H-labelled amino acid were discrete, and free from cross-contamination. These results prove that glutamine is the precursor amino acid of pyrrolid-2-one-5-carboxylic acid at the N-termini of the mature MOPC-104E lambda(1), RPC-20 lambda(1) and MOPC-315 lambda(2) L-chains. Thus the formation of pyrrolid-2-one-5-carboxylic acid by cyclization of glutamine is a post-translational event which occurs after, or concomitant with, cleavage of the extra piece from the precursor to yield the mature L-chain. The variable (V) regions (110 amino acid residues) of mouse lambda L-chains are quite similar: when compared with that of MOPC-104E lambda(1) chain, the V-region of RPC-20 lambda(1) chain differs in one residue, and the V-region of MOPC-315 lambda(2) chain differs in 11 residues. The partial sequence data show that the N-terminal extra pieces of the two lambda(1) L-chain precursors have, so far, identical partial sequences; the extra piece of the lambda(2) L-chain precursor differs from these in at least three out of 19 positions.     

The formation of pyrrolid-2-one-5-carboxylic acid at the N-terminus of immunoglobulin G heavy chain

We propose that pyrrolid-2-one-5-carboxyl-tRNA is not involved in the initiation of protein synthesis in eukaryotic cells and that the N-terminal pyrrolid-2-one-5-carboxylic acid group of an IgG (immunoglobulin G) (that secreted by the mouse plasmacytoma Adj PC5) is formed by the enzymic cyclization of the N-terminal glutamine of the heavy chain of the completed IgG molecule and that the cyclization takes place inside the cell. We base these conclusions on the following evidence. (1) Pyrrolidonecarboxyl-tRNA was not found in incorporation experiments with rat liver preparations and [U-(14)C]-pyrrolidonecarboxylic acid, glutamic acid and glutamine, even though an incorporation extent of less than 2% of the total products could have been detected. (2) Double-labelling experiments showed that less than 8% of the nascent peptides of heavy chains (those obtained by precipitation by the antibody to Fc fragment) began with pyrrolidonecarboxylic acid. (3) Further double-labelling experiments showed that 60-66% of the heavy chains of the completed intracellular IgG molecule began with pyrrolidonecarboxylic acid after both 1 and 5h of labelling. (4) The IgG, after secretion by plasmacytoma Adj PC5, was found to have the sequence [unk]Glu- Val-Gln-Leu- at the N-termini of the heavy chains.     

The N-terminal sequence of the heavy chain of rabbit immunoglobulin IgG

The absence of an N-terminal amino acid with a free alpha-amino group from the heavy chain of rabbit immunoglobulin IgG has been confirmed and no evidence could be found of a blocking formyl, acetyl or propionyl group. The N-terminal amino acid appears to be pyrrolid-2-one-5-carboxylic acid (PCA) in all molecules. A mixed amino acid sequence follows in the approximate proportions: PCA-Ser-Val-Glu-Glu-Ser-Gly-Gly-Arg, 50%; PCA-Ser-Leu-Glu, 20%; PCA-Glu(NH(2)), 20%. The heavy chains of a purified antibody, namely anti-(human serum albumin), and of immunoglobulin IgG from a rabbit homozygous at the allotypic loci both showed a similar mixed N-terminal sequence.     

Amino acid sequence of the N-terminal non-collagenous segment of dermatosparactic sheep procollagen type I.

The non-collagenous N-terminal segment of type I procollagen from dermatosparactic sheep skin was isolated in the form of the peptide Col 1 from a collagenase digest of the protein. The peptide has a blocked N-terminus, which was identified as pyrrolid-2-one-5-carboxylic acid. Appropriate overlapping fragments were prepared from reduced and alkylated peptide Col 1 by cleavage with trypsin at lysine, arginine and S-aminoethyl-cysteine residues and by cleavage with staphylococcal proteinase at glutamate residues. Amino acid sequence analysis of these fragments by Edman degradation and mass spectrometry established the whole sequence of peptide Col 1 except for a peptide junction (7--8) and a single Asx residue (44), and demonstrated that peptide Col 1 consists of 98 amino acid residues. The N-terminal portion of peptide Col 1 (86 residues) shows an irregular distribution of glycine, whereas the C-terminal portion (12 residues) possesses the triplet structure Gly-Xy and is apparently derived from the precursor-specific collagenous domain of procollagen. The central region of the peptide contains ten cysteine residues located between positions 18 and 73 and shows alternating polar and hydrophobic sequence elements. The regions adjacent to the cysteine-rich portion have a hydrophilic nature and are abundant in glutamic acid. The data are consistent with previous physicochemical and immunological evidence that distinct regions at the N- and C-termini of the non-collagenous domain possess a less rigid conformation than does the central portion of the molecule.     

The N- and C-terminal amino acid sequences of the heavy chain from a pathological human immunoglobulin IgG

The heavy chain of a pathological human immunoglobulin IgG and also the Fd fragment have been isolated. No free alpha-amino group was present on either and the N-terminal sequence of both has been identified as pyrrolid-2-one-5-carbonylvalylthreonine. Splitting at the four methionine residues of the heavy chain with cyanogen bromide gave five fractions. The fraction from the C-terminal end of the chain was isolated in high yield and the amino acid sequence was: His-Glu-Ala-Leu-His-Asp(NH(2))-His-Tyr-Thr-Glu(NH(2))-Lys-Ser-Leu-Ser-Leu-Ser-Pro-Gly These results give strong support to the view that the heavy chain of immunoglobulin is a single peptide chain.     

One cell–one immunoglobin. Origin of limited heterogeneity of myeloma proteins

Plasma-cell tumour 5563 forms a single molecular species of immunoglobulin IgG(2)a, i.e. one variant of heavy chain and one variant of light chain. The molecules formed are labile and undergo alterations in charge properties, which rapidly lead to heterogeneity of the myeloma protein after synthesis. The single immunoglobulin species originally formed is found only after the shortest time-intervals tested, i.e. 10min incubation. Two types of changes in charge properties take place: (1) The originally formed protein (component o) is converted via an intermediate o' into the most basic form of 5563 myeloma protein found in serum (component a). Charge differences between these components are suppressed at pH8.9, but can be studied by chromatography at pH6.5 or by analysis of isoelectric points by isoelectric focusing in polyacrylamide gel. The conversion of components o and o' into component a apparently commences soon after assembly of the molecules and proceeds to completion extracellularly. (2) The second type of charge difference that distinguishes components a, b, c and d is exhibited over the pH range 6.0-8.9, but not at acid pH, and has been studied by electrophoresis at pH8.9, by chromatography and by isoelectric focusing. Conversion of component a into components b, c, d and e is only partial so that all five components can be found at decreasing concentrations in serum. Both types of charge alteration can be effected in vitro in the presence of serum, with optimum pH8.0. None of the charge differences could be attributed to the secretion process, since a component with the same isoelectric point as component o was found in secreted myeloma protein (1h). We have found no evidence to support the idea that the first type of change from component o to component a is due to ring formation of N-terminal [(14)C]glutamine into pyrrolid-2-one-5-carboxylic acid; however, our findings do not exclude this process happening very rapidly to a precursor of component o, possibly the polypeptide chain during or immediately after synthesis. In studying this point we noted that not only the heavy chains but also the kappa-type light chain of mouse 5563 myeloma protein have a blocked N-terminus.     

The design and production of semisynthetic ribonucleases with increased thermostability by incorporation of S-peptide analogues with enhanced helical stability

Recent work has shown that, with synthetic analogues of C-peptide (residues 1-13 of ribonuclease A), the stability of the peptide helix in H2O depends strongly on the charge on the N-terminal residue. We have asked whether, in semisynthetic ribonuclease S reconstituted from S-protein plus an analogue of S-peptide (1-15), the stability of the peptide helix is correlated with the Tm of the reconstituted ribonuclease S. Six peptides have been made, which contain Glu9----Leu, a blocked alpha-COO- group (-CONH2), and either Gln11 or Glu11. The N-terminal residue has been varied; its charge varies from +2 (Lys) to -1 (succinyl-Ala). We have measured the stability of the peptide helix, the affinity of the peptide for S-protein (by C.D. titration), and the thermal stability of the reconstituted ribonuclease S. All six peptide analogues show strongly enhanced helix formation compared to either S-peptide (1-15) or (1-19), and the helix content increases as the charge on the N-terminal residue changes from +2 to -1. All six peptides show increased affinity for S-protein compared to S-peptide (1-19), and all six reconstituted ribonucleases S show an increase in Tm compared to the protein with S-peptide (1-19). The Tm increases as the charge on residue 1 changes from +2 to -1. The largest increment in Tm is 6 degrees. The results suggest that the stability of a protein can be increased by enhancing the stability of its secondary structure.     

Structures of shorthorn sculpin antifreeze polypeptides

The amino acid sequences of the two major antifreeze polypeptides (AFP) from the shorthorn sculpin have been determined using an automatic protein sequencer and enzymic digestion. These two polypeptides, SS-3 and SS-8, consist of 33 and 45 amino acid residues respectively. The N-terminal methionyl residue is blocked in both the polypeptides. When aligned for maximum structural similarity these two AFP are 80% homologous, and there appears a deletion of 12 amino acid residues at the N-terminal portion of SS-3. Like the winter flounder AFP, both the sculpin AFP also contain the 11-amino-acid repeat sequences. The secondary structure of the sculpin AFP is mainly alpha-helical as deduced from circular dichroic spectral data. The helical content of SS-8 is high (73%), while that of SS-3 is moderate (about 45%). The latter exhibits a relatively weak antifreeze activity. Removal of the blocked N-terminal residue in SS-8 did not alter the helical content significantly but did reduce the antifreeze activity. Helical contents of proteolytically generated fragments of AFP are much lower, and they are devoid of activity. The alpha-helix in the SS-8 component is seen to be amphiphilic in character. The relevance of this feature to the mechanism of the antifreeze action is briefly discussed.     

Cyclization of N-terminal S-carbamoylmethylcysteine causing loss of 17 Da from peptides and extra peaks in peptide maps

Enzymatic digests of proteins S-alkylated with iodoacetamide may contain peptides with N-terminal S-carbamoylmethylcysteine. These can be partly converted to a form with 17 Da lower mass and increased HPLC retention. Proof by synthesis supported by MS/MS and NMR spectroscopy was used to show that N-terminal S-carbamoylmethyl-L-cysteine can cyclize, losing NH3 to form an N-terminal residue of (R)-5-oxoperhydro-1,4-thiazine-3-carboxylic acid. The abbreviation Otc is proposed for the (R)-5-oxoperhydro-1,4-thiazine-3-carbonyl residue. The rate of cyclization is significant in 0.1 M NH4HCO3 at 37 degrees C, with the half-life of the acyclic form being 10-12 h for several peptides tested. This is similar to the rate at which N-terminal pyroglutamate forms from N-terminal glutamine.     

Roles of N-terminal pyroglutamate in maintaining structural integrity and pKa values of catalytic histidine residues in bullfrog ribonuclease 3

Many proteins and bioactive peptides contain an N-terminal pyroglutamate residue (Pyr1). This residue reduces the susceptibility of the protein to aminopeptidases and often has important functional roles. The antitumor ribonuclease RC-RNase 3 (RNase 3) from oocytes of Rana catesbeiana (bullfrog) is one such protein. We have produced recombinant RNase 3 containing the N-terminal Pyr1 (pRNase 3) and found it to be indistinguishable from the native RNase 3 by mass spectrometry and a variety of other biochemical and immunological criteria. We demonstrated by NMR analysis that the Pyr1 of pRNase 3 forms hydrogen bonds with Lys9 and Ile96 and stabilizes the N-terminal alpha-helix in a rigid conformation. In contrast, the N-terminal alpha-helix becomes flexible and the pKa values of the catalytic residues His10 and His97 altered when Pyr1 formation is blocked by an extra methionine at the N terminus in the recombinant mqRNase 3. Thus, our results provide a mechanistic explanation on the essential role of Pyr1 in maintaining the structural integrity, especially at the N-terminal alpha-helix, and in providing the proper environment for the ionization of His10 and His97 residues for catalysis and cytotoxicity against HeLa cells.     

Structural analysis of the minor human hemoglobin components: Hb AIa1, Hb AIa2 and Hb AIb

Human hemolysate contains several minor hemoglobin components, including Hb AIa1, Hb AIa2, Hb AIb and Hb AIc which are post-translational modifications of the major component, Hb A0. Hb AIc is known to contain glucose attached to the N terminus of the beta chains by a ketoamine linkage. We separated the alpha and beta globin chains from purified Hb AIa1, Hb AIa2 and Hb AIb by ion-exchange chromatography. The beta chains were reducible by sodium borohydride and gave a positive thiobarbituric acid test. These results indicated that they are modified by ketoamine-linked carbohydrate. In addition, phosphate analysis revealed 1.5 phosphate residue associated with each beta AIa1 chain and 1 phosphate residue with each beta AIa2 chain. Hb AIa1, Hb AIa2 and Hb AIb were all found to be contaminated by non-globin proteins. Protein-sequencing approaches demonstrated that the N termini of beta AIa1, beta AIa2 and beta AIb were blocked. In support of this conclusion, analysis of tryptic digests of beta AIa2 and B AIb revealed modified N-terminal peptides. We conclude that, like Hb AIc, components Hb AIa1, Hb AIa2 and Hb AIb also contain a sugar moiety linked to the N terminus of the beta chain.     

A kininase and a kinin-converting enzyme: two distinct alpha aminoacyl peptide hydrolases from bovine lung

Two closely related but different aminopeptidases from bovine lung have been isolated and characterized. The first aminopeptidase, which removes the N-terminal arginine residue from L-arginyl-L-prolyl-L-proline, bradykinin, and des-[Arg9]-bradykinin, has kininase activity; it has a pH optimum of 8.0, is stimulated by Mn2+, and its molecular weight in dilute buffers is slightly greater than 240,000 daltons. The second aminopeptidase, which converts kallidin to bradykinin, has kinin-converting activity; it has a pH optimum of 6.8, is stimulated by Co2+, and its molecular weight in dilute buffers is 250,000 daltons. The kinin-converting enzyme is blocked from action when the N-terminal penultimate residue is proline.     

Limited proteolysis of human erythrocyte Ca2+-ATPase in membrane-bound form. Identification of calmodulin-binding fragments

Water-soluble and membrane-bound calmodulin-binding polypeptides formed upon limited proteolysis of erythrocyte ghosts were isolated by means of affinity chromatography. Immune blotting revealed that all isolated fragments originated from Ca2+-ATPase. Among the fragments obtained those having formed an acylphosphate intermediate were identified. The N-terminal residue of purified intact Ca2+-ATPase was shown to be blocked (probably acylated).     

中国南海侧扁软柳珊瑚中孕甾烷类化学成分的研究(英文)

从南海侧扁软柳珊瑚Subergorgia suberosa的二氯甲烷-甲醇提取物中首次分离鉴定了8个孕甾烷类化合物,经波谱鉴定为3β-O-palmitoyl-pregn-5-ene-20-one-3-ol (1),3β-O-palmitoyl-5α-pregn-20-one-3-ol (2),5α-pregn-1-ene-3,20-dione (3),3β,5α-pregn-20-one-3-ol (4),3β-pregn-5-ene-20-one-3-ol (5),3β,5β-pregn-20-one-3-ol (6),5β-pregn-3,20-dione (7),pregn-4-ene-3,20-dione (8).其中化合物1,2为新化合物.     

Evidence for a role of specific isoacceptor species of tRNA in amino acid transport.

Soybean leghemoglobins ā and b?were compared by microscale peptide mapping after heme removal with acid-acetone. Maps generated by trypsin or the combined action of trypsin and thermolysin indicated a large amount of homology between the proteins with the only variations detected being the N-terminal peptides. The N-terminal tryptic peptide of leghemoglobin b? was found to be both blocked and to lack the first amino acid of the corresponding leghemoglobin ā peptide. Nuclear magnetic resonance and gas chromatography/mass spectroscopy studies showed that the N-terminal of leghemoglobin b? was N-acetyl-alanine. It is possible that leghemoglobin b? arises from leghemoglobin ā by a two-stage modification involving cleavage of the N-terminal valyl residue and subsequent acetylation of the exposed alanyl residue.     

An improved procedure, involving mass spectrometry, for N-terminal amino acid sequence determination of proteins which are N alpha-blocked.

A modification to a previously described procedure [Gray & del Valle (1970) Biochemistry 9, 2134-2137; Rose, Simona & Offord (1983) Biochem. J. 215, 261-272] for mass-spectral identification of the N-terminal regions of proteins is shown to be useful in cases where the N-terminus is blocked. Three proteins were studied: vesicular-stomatitis-virus N protein, Sendai-virus NP protein, and a rabbit immunoglobulin lambda-light chain. These proteins, found to be blocked at the N-terminus with either the acetyl group or a pyroglutamic acid residue, had all failed to yield to attempted Edman degradation, in one case even after attempted enzymic removal of the pyroglutamic acid residue. The N-terminal regions of all three proteins were sequenced by using the new procedure.     

Nucleotide sequence of cloned cDNA coding for pumpkin 11-S globulin beta subunit

cDNA coding for preproglobulin beta, a precursor protein of 11-S globulin beta subunit, was cloned and the nucleotide sequence has been determined. The sequence covers the whole coding region (1440 base pairs) with 5' and 3' noncoding region (30 and 214 base pairs, respectively). The deduced amino acid sequence of preproglobulin beta consists of a 21-amino-acid N-terminal signal peptide, preceding the acidic gamma polypeptide region (275 amino acids) and the subsequent basic delta region (184 amino acids). The site for post-translational cleavage of the precursor polypeptide to make the gamma and delta chains is estimated to be located between the asparagine-glycine residues. The N-terminal amino acid of the gamma chain of mature 11-S globulin beta subunit was reported to be blocked by 5-oxoproline (pyroglutamic acid) [Ohmiya et al. (1980) Plant Cell Physiol. 21, 157-167]. It was shown that the blocked N-terminal amino acid is coded as a glutamine residue. The derived amino acid sequence was also compared with those of precursor proteins of other 11-S globulins such as soybean glycinin, cotton beta globulin, pea legumin and rape 11-S globulin by dot matrix analysis.     

Tau-related protein present in paired helical filaments has a decreased tubulin binding capacity as compared with microtubule-associated protein tau

We have isolated, after exhaustive detergent treatments, a 33 kDa tau-related protein isolated from paired helical filaments from Alzheimer's disease patient brains. The N-terminal sequence of the 33 kDa protein begins at residue 71 of the sequence described for human fetal tau protein. This truncated form of tau is not the consequence of the translation of a tau RNA lacking a region at its 5' end, as measured by primer extension analyses, suggesting that the 33 kDa protein must be generated by proteolysis of previously synthesized tau. This tau-related protein has only one blocked cysteine residue and also has a decreased tubulin binding capacity as compared with that of tau protein.     

The Ubiquitin-conjugating Enzyme (E2) Ube2w Ubiquitinates the N Terminus of Substrates

Attachment of ubiquitin to substrate is typically thought to occur via formation of an isopeptide bond between the C-terminal glycine residue of ubiquitin and a lysine residue in the substrate. In vitro, Ube2w is nonreactive with free lysine yet readily ubiquitinates substrate. Ube2w also contains novel residues within its active site that are important for its ability to ubiquitinate substrate. To identify the site of modification, we analyzed ubiquitinated substrates by mass spectrometry and found the N-terminal -NH₂ group as the site of conjugation. To confirm N-terminal ubiquitination, we generated lysine-less and N-terminally blocked versions of one substrate, the polyglutamine disease protein ataxin-3, and showed that Ube2w can ubiquitinate a lysine-less, but not N-terminally blocked, ataxin-3. This was confirmed with a second substrate, the neurodegenerative disease protein Tau. Finally, we directly sequenced the N terminus of unmodified and ubiquitinated ataxin-3, demonstrating that Ube2w attaches ubiquitin to the N terminus of its substrates. Together these data demonstrate that Ube2w has novel enzymatic properties that direct ubiquitination of the N terminus of substrates.