The heparin-binding lectin from ovine placenta: purification and identification as histone H4

The heparin-binding lectin complex from ovine placental cotyledons was purified by affinity chromatography on heparin-agarose column. It showed three protein bands, which had molecular weights of 13000, 15000 and 17000 by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and the presence of DNA by agarose gel electrophoresis. The protein components of the complex were separated by reverse-phase HPLC. The minimum inhibitory concentrations of glycosaminoglycans were significantly different for the lectin complex and the separated proteins, suggesting affinity changes upon DNA binding. The haemagglutinating activity specificity allowed the characterization of the fraction with a molecular weight of 13000 as the heparin-binding lectin. This protein was identified as histone H4 by internal sequencing, thus showing that this is the histone responsible for the heparin-binding property of the complex. The accompanying proteins were tentatively identified as histones H2A and H2B.

A sialic acid-binding lectin from ovine placenta: purification, specificity and interaction with actin

A sialic-acid-specific lectin from ovine placental cotyledons was purified by affinity chromatography on bovine submaxillary mucin-agarose followed by gel filtration, and it showed a molecular weight of 65000 by sodium dodecylsulfate-polyacrylamide gel electrophoresis. This lectin has the capacity to interact with actin, since it binds to actin-F in a cosedimentation assay and it acts as a mediator in the binding of actin to the affinity column. The lectin agglutinated rabbit and rat erythrocytes, but not human A, B or O erythrocytes. Haemagglutination inhibition assays of different saccharides, glycoproteins and glycolipids indicate that this lectin has affinity for sialic acid, which is enhanced by its O-acetylation. The N-terminal sequence of the protein shows 92% identity with rabbit and porcine uterine calreticulin.

Detection and characterization of an ovine placental lactogen stable intermediate in the urea-induced unfolding process

The urea-induced equilibrium unfolding of ovine placental lactogen, purified from ovine placenta, was followed by size-exclusion chromatography, far-UV CD, and intrinsic tryptophan fluorescence. The data obtained by each of these methods showed a poor fit to a two-state model involving only a native and an unfolded form. A satisfactory fit required, instead, a model that involved a stable, partially folded form in addition to the native and unfolded ones. The results obtained from the best-fitting theoretical curves for the three-state model indicated that this intermediate state, which is the predominant species in solution at 3.6 M of urea activity, is compact, largely alpha-helical, and changes considerably the native-like tertiary packing around its tryptophan residues. These findings suggest that this stable intermediate exhibits properties similar to those that characterize the molten globule state.

Identification of a tyrosine residue in ovine placental lactogen as essential for its binding to receptors

Nitration of ovine placental lactogen (oPL) with a 10-fold molar excess of tetranitromethane over protein content resulted in the modification of 0.8 tyrosine residue. No conformational changes were observed by either fourth-derivative spectral analysis or circular dichroism. Nitration significantly decreased the binding capacity of the hormone to lactogenic and somatogenic rat liver receptors. This binding capacity was not restored by reduction of the nitro groups, thus indicating that the decrease was not due to the difference in pK between tyrosine and nitrotyrosine. The nitrotyrosine-containing peptide was isolated from a tryptic digest by HPLC and its modification extent was of 67%, which is consistent with the decrease in binding capacities (65% and 70%). Its amino acid sequence was determined and the modified tyrosine residue was identified as Tyr-46. These results provide the first evidence of the involvement of a tyrosine residue in the binding of oPL to both lactogenic and somatogenic receptors. This tyrosine appears to be a shared binding epitope between oPL and the prolactins.

Modification of arginine residues in ovine prolactin by 1,2-cyclohexanedione. Effect on binding capacity to lactogenic receptors

The reactivity of arginine residues in ovine prolactin was studied by reaction with 1,2-cyclohexanedione. Kinetic analysis of the data showed a good fit with two simultaneous pseudo-first-order equations with apparent velocity constants of 0.28 and 1.2 x 10(-2) min-1, corresponding to 1.8 'fast' and 8.7 'slow' residues, respectively. Modification led to a decrease in binding capacity to lactogenic rat liver receptors, and apparently the modification of the two 'fast' reacting arginine residues is responsible for the rapid loss of this capacity. The presence of a non-reacting arginine has been described in human and bovine growth hormones, and it is located near the carboxy-terminus. This lack of reactivity is probably due to the formation of a salt bridge, since the arginine residue becomes susceptible to modification once the peptide is separated from the rest of the molecule. This salt bridge is absent in ovine prolactin, since the homologous arginine residue is reactive with cyclohexanedione. This result suggests that there could be a difference between the three-dimensional structure of ovine prolactin and of the growth hormones, at least near the carboxy-terminal region of the molecule.

Selective modification of tryptophan-150 in ovine placental lactogen

1. Ovine placental lactogen was modified by reaction with o-nitrophenylsulfenyl chloride. Fluorescence measurements indicated that one of the two tryptophan residues of the molecule had reacted. Besides, there was some reagent not covalently bound. 2. The reagent was covalently bound to Trp-150. No evidence of modification of Trp-90 was found. 3. Binding capacity to lactogenic as well as somatogenic receptors was diminished but not abolished upon modification, indicating that absolute molecular integrity of Trp-150 is not required for binding. 4. This behavior is similar to that of the tryptophan residues of ovine prolactin.

Chemical modification of ovine prolactin with N-acetylimidazole

Reaction of ovine prolactin (oPRL) with a 150-fold molar excess of N-acetylimidazole over protein content resulted in the modification of 2.5 tyrosine residues and 1.2 lysine residues. Acetylation greatly decreased the in vitro binding capacity to lactogenic sites. This binding capacity was partially restored by ammonium bicarbonate treatment, which removes O-acetyl groups from tyrosine residues but not N-acetyl groups from lysine residues. The modification extent of the tyrosine residues was determined. The results suggest that acetylation of tyrosine 44 or of tyrosine 96 is likely to be responsible for the decrease in binding activity of acetylated oPRL, and that one of these residues may play a role in the interaction of oPRL with lactogenic receptors.

Chemical modification of human growth hormone with N-acetylimidazole. Effect on binding capacity to lactogenic and somatogenic receptors

The effect of acetylation of tyrosine residues on the binding capacity of human growth hormone (hGH) to rat liver lactogenic and somatogenic receptors was studied. When 3.7 tyrosine and 4.8 lysine residues were acetylated with N-acetylimidazole, both the in vivo and the in vitro capacities of hGH to compete with 125I-labeled bovine growth hormone for somatogenic binding sites greatly decreased. Acetylation also affected the in vitro binding capacity to lactogenic sites. Most of the somatogenic binding activity was recovered by hydroxylamine treatment, which removes O-acetyl groups from tyrosine residues but not N-acetyl groups from lysine residues. The same treatment partially restored lactogenic binding capacity. The reactivity of hGH tyrosine residues to N-acetylimidazole, together with previous evidence, suggests that: (a) Tyrosine residues 160 and 164, when acetylated, are likely to be responsible for the low binding activity of acetylated hGH. (b) Tyrosine 160 may play a significant role in hGH interaction with lactogenic receptors.

Modification of arginine residues in human growth hormone by 1,2-cyclohexanedione: effects on the binding capacity to lactogenic and somatogenic receptors

Reactivity of arginine residues in human growth hormone was studied by reaction with 1,2-cyclohexanedione. Kinetic analysis of the data showed a good fit to a pseudo first order curve, with an apparent velocity constant k = 1.26 x 10(-2) min-1 and a maximum modification of 9.6 out of the 11 arginines of the molecule. Modification led to a decrease in binding capacity to both lactogenic and somatogenic rat liver receptors. In either case Tsou plots suggest that the modification of two arginine residues is responsible for this behavior, although it cannot be ascertained whether the two relevant residues are the same for both receptor types. Circular dichroism studies indicated no apparent changes in protein conformation in the modified hormone. Binding capacity was restored upon regeneration of arginines by incubation with Tris-HCl buffer. Only the carboxy-terminal peptide was isolated by HPLC from a tryptic digest of succinylated Arg-modified hGH, indicating that 183 is the nonreacting arginine residue.

Ovine prolactin and human growth hormone derivatives. Specific modification of their alpha-amino groups

The alpha-amino group of ovine prolactin (oPRL) and human growth hormone (hGH) was selectively modified by transamination with glyoxylic acid. No difference was found in the binding capacity of transaminated oPRL to rat liver lactogenic receptors with respect to its control, although both samples showed a decrease in its binding capacity with reference to the native hormone. This decrease was due to conformational changes caused by the reaction conditions and not by the transamination itself, as shown by the circular dichroism spectra. Transaminated hGH retained the full binding capacity of the hormone. These results suggest that the alpha-amino group is not relevant for the binding to lactogenic liver receptors in both lactogenic hormones.

Selective reduction of the disulfide bonds of ovine placental lactogen

Reduction and carbamidomethylation of two of the three disulfide bridges of ovine placental lactogen was accomplished by the use of 20-fold molar excess of dithiothreitol over protein disulfide content. The derivative retained its binding capacity to somatogenic as well as lactogenic rat liver receptors, although the latter was somewhat diminished. The two disulfide bonds exposed to the reducing agent are those located near the carboxy- and amino-terminus, while the larger loop remained intact after reduction. This behaviour is similar to that of bovine growth hormone, where the larger loop was also more resistant to reduction.

Identification of intramolecular crosslinks in bovine growth hormone after two-step modification with 1,5-difluoro-2,4-dinitrobenzene

Derivatives of bovine growth hormone, containing monoaminotyrosyl residues in positions 35, 42 and 174, were treated at pH 3.6 with a bifunctional reagent, 1,5-difluoro-2,4-dinitrobenzene. Under these conditions aminotyrosyl groups reacted. On changing the pH to 9.3, the second fluorine atom of the reagent was substituted with the sterically adjacent side groups of lysine, since the excess of reagent had been previously removed. The modified protein underwent cyanogen bromide treatment. Peptides containing the crosslinks were purified from tryptic digests of the cyanogen bromide fragments by HPLC. Results show that aminoTyr 174 was able to form dinitrophenylene bridges with Lys 111, Lys 29 and Lys 170. AminoTry 35 was found crosslinked to Lys 29. Taking into account the size of the reagent, it may be inferred that Lys 29, 111 and 170 are located at approximately 5 A from Tyr 174 in the bovine growth hormone molecule.

Evidence for the steric proximity of Tyr 174 and Lys 111 in bovine growth hormone

Bovine growth hormone was modified by reaction with 1,5-difluoro-2,4-dinitrobenzene under conditions favouring production of intramolecularly crosslinked derivatives from monomeric molecules. The monomeric fraction, isolated by chromatography on Sephadex G-100, was oxidized or reduced and carbamidomethylated and trypsin digested. The resulting peptides were fractionated on SP-Sephadex and further purified by peptide mapping or HPLC. Two modified peptides containing sequences 108-112 or 108-113 and 171-176 of bGH were obtained, including a dinitrophenylene bridge between lysine 111 and tyrosine 174, thus suggesting the stereochemical proximity of these residues.

Modification of arginines in bovine growth hormone

Treatment of bovine growth hormone with 1,2-cyclohexanedione - in borate buffer - selectively modified 11.8 out of the 13 arginines in the molecule. Kinetic analysis of the data showed a good fit to a pseudo first-order curve, with an apparent velocity constant k: 2 X 10(-2) min-1. The modification brought about a complete loss of bovine growth hormone capacity to compete with 125I-labelled hormone for rat liver binding sites. Circular dichroism studies indicated no apparent changes in protein conformation in the modified hormone. Full binding capacity was restored upon regeneration of arginines by hydroxylamine treatment. These results suggest that one or more arginines are involved in the binding of bovine growth hormone to its specific receptors. The non-reactive arginine was identified as arginine 181.

Separation and analysis of the major forms of plasma fibronectin

Human plasma fibronectin exists in circulation in multiple molecular forms that are distinguishable by SDS-polyacrylamide gel electrophoresis (zone I, approx. 450 kDa dimers; zone II, 190-235 kDa; Zone III, 146-175 kDa). (Chen, A.B., Amrani, D.L. and Mosesson, M.W. (1977) Biochim. Biophys. Acta 493, 310-322). We report here on investigations of plasma fibronectin that had been purified from the 'heparin-precipitable fraction' of plasma by DEAE-cellulose chromatography using buffers containing a chaotropic salt (KSCN). Zone I fibronectin and zone II fibronectin were subsequently separated by Sepharose CL-6B chromatography in the presence of 0.3 M KSCN. Electrophoresis of reduced zone I fibronectin dimers showed the presence of three types of subunits (i.e., 220 kDa, 215 kDa, 207 kDa), evidently all having the same NH2-terminal sequence. Subunits of this size were also found in reduced zone II fibronectin, as well as another polypeptide of 190 kDa, the latter amounting to under 5% of the total. Unreduced zone I fibronectin was resolved by gel electrophoresis into a doublet. The upper component amounted to approx. 90% of the total and was comprised of 220 kDa and/or 215 kDa subunits; the lower component contained 207 kDa plus a 220 kDa or 215 kDa subunit. Scanning transmission electron microscopy indicated that under physiologic conditions zone II fibronectin molecules, like those in zone I, exist as pleiomorphic, loosely folded structures (approx. 16 X 8-12 nm) that are somewhat smaller than dimeric zone I molecules (approx. 24 X 16 nm). Circular dichroic spectral analyses suggests that both types have similarly folded local domains. Affinity chromatography experiments revealed a relative decrease in the binding of zone II fibronectin to gelatin but no difference from zone I fibronectin with respect to heparin or fibrin binding.

Carboxy-terminal amino acid sequence of a human fibrinogen gamma-chain variant (gamma')

A normal human fibrinogen gamma-chain variant, termed gamma', is larger than the gamma chain (51 500 vs. 49 500) due to an extended COOH-terminal sequence. The extended COOH-terminal cyanogen bromide peptide (CNBr e') was isolated by high-pressure liquid chromatography, and its amino acid sequence was determined. Comparison with the corresponding COOH-terminal gamma-chain peptide (CNBr e) showed that the last four amino acids of the gamma chain were replaced in gamma' chains by a 20-residue fragment rich in aspartic and glutamic acids, having the sequence Val-Tyr-Pro-Glu-His-Pro-Ala-Glx-Thr-Glx-Tyr-Asx-Ser-Leu-Arg-Pro-Glx-Asx-Asx-Leu . Mutant gamma chains (gamma Paris I) from a congenitally dysfunctional fibrinogen molecule (fibrinogen Paris 1) express both gamma and gamma' features, suggesting that both gamma and gamma' chains are produced from a single gene. If this suggestion is correct, the observed differences in amino acid sequence could be explained by the existence of different mRNAs for gamma and gamma' chains, respectively, which are transcribed from one gene by differential RNA splicing.

Human plasma fibrinogen heterogeneity: evidence for an extended carboxyl-terminal sequence in a normal gamma chain variant (gamma')

Two types of normal human plasma fibrinogen--peak 1 and peak 2--are distinquishable by DEAE-cellulose gradient elution chromatography. The elution characteristics of peak 2 fibrinogen, which amounts to about 15% of the total, are attributable to the presence of a gamma chain variant, gamma', which is more negatively charged than gamma chains and makes up about half of all such chains in that peak [Mosesson M. W., Finlayson, J. S. & Umfleet, R. A. (1972), J. Biol. Chem. 247, 5223-5227]. Analyses of reduced S-carboxymethylated fibrin that had first been incubated in the presence of Factor XIIIa plus the fluorescent amine donor dansylcadaverine (DNScad) showed that the same amount of this compound could be incorporated covalently into either type of gamma chain. Furthermore, the DNScad-labeled COOH-terminal CNBr fragment (CNBr e) derived from the S-carboxymethylated gamma chain was smaller than the DNScad-labeled fragment (CNBr e') from the gamma' chain (Mr, 3200 and 4900) by about the same amount as the difference in size between the respective parent chains (Mr, 49,400 and 51,500). DNScad-CNBr e or DNScad-cNBR e' could be further cleaved by trypsin to yield a smaller fluorescent fragment corresponding to the penultimate tryptic gamma chain peptide containing the DNScad-glutamine acceptor and lysine donor crosslinking functions. The COOH-terminal amino acids of gamma and gamma' chains were valine and leucine, respectively. The rates of Factor XIIIa-catalyzed crosslinking of peak 1 and peak 2 fibrin were the same, but peak 1 fibrin gamma chains formed only one species of crosslinked dimer (gamma gamma) whereas peak 2 fibrin gamma chains yielded three (gamma gamma, gamma gamma', gamma'gamma'). We conclude that gamma' chains are functionally normal but have an extended COOH-terminal sequence accounting for their more negative charge and larger size relative to gamma chains.

Proteoglycans from bovine proximal humeral articular cartilage. Structural basis for the polydispersity of proteoglycan subunit

Polydisperse proteoglycan subunit from bovine proximal humeral articular cartilage has been separated into a series of relatively monodisperse fractions which have been chemically and physically characterized. The proteoglycan subunit species of the lowest molecular weight contains the least chondroitin sulfate and had an amino acid composition relatively low in serine and glycine and relatively high in cysteine, methionine, and aspartic acid, almost identical to that of the hyaluronic acid-binding region of proteoglycan subunit isolated by Heinegard and Hascall (Heinegard, D., and Hascall, V.C. (1974) J. Biol. Chem. 249, 4250-4256). The molecular weight of proteoglycan subunit increases in proportion to its chondroitin sulfate content. As the molecular weight and chondroitin sulfate content of proteoglycan subunit increase, there is a parallel increase in the serine and glycine contents, and a decrease in the cysteine, methionine, and aspartic acid contents of proteoglycan subunit core protein. The pattern of polydispersity observed strongly supports the concept that proteoglycan subunit core protein contains a hyaluronic acid-binding region of constant size and composition and a polysaccharide attachment region of variable length and composition, composed of repeating peptide sequences containing serine and glycine in equimolar amounts.

Partial amino acid sequence of an IgA2 human immunoglobulin heavy chain

The amino acid sequence of the heavy chain of an IgA2, AIm(1) polymeric myeloma protein (Avil) was studied. Altogether, sequence data were obtained for some 130 residues. Including the amino acids placed by homology with IgA1, this accounts for some 170 residues, thus representing more than one-third of the alpha2 chain. The sequence includes 26 amino acids from the amino-terminal end (V-H III), and 25 residues at the "hinge" region. Of a total of 17 cysteine residues, 14 were located in regions of the molecule which were identical or homologous in the alpha1 and alpha2 chains. These striking homologies, together with the results obtained by diagonal maps of classes of IgA. Study of the cysteine-containing peptides of the J chain are consistent with the conclusion that the J chains associated with different classes of immunoglobulins are identical.

"Alpha chain disease" protein def: internal deletion of a human immunoglobulin A1 heavy chain

Protein Def is a human alpha chain disease protein related to alpha1 immunoglobulin heavy chain. The molecular weight of the polypeptide portion of the monomeric molecule is 29,300, which is a little greater than half of a normal alpha1 chain. The NH(2)-terminal of the polypeptide is heterogenous and, after a short segment corresponding to the variable region, displays a gap which comprises the C(H)1 constant domain. Normal synthesis resumes at a valine residue in the hinge region just before a segment which contains a partially duplicated fragment and the interheavy disulfide bonds. From there on, the molecule is apparently normal. Protein Def is therefore synthesized as an internally deleted alpha1 heavy chain, followed by postsynthetic amino-terminal proteolysis. It is postulated that codon(s) specifying valine at the hinge region may be a recognition site for reinitiating synthesis after internal gaps equivalent to position 216 in gamma chain disease proteins.