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M Baron

Publications and source records attributed to M Baron.

At least 19 recordsLinked to original sources
PubMed1992

The three-dimensional structure of the tenth type III module of fibronectin: an insight into RGD-mediated interactions.

The solution structure of the tenth type III module of fibronectin has been determined using nuclear magnetic resonance techniques. The molecule has a fold similar to that of immunoglobulin domains, with seven beta strands forming two antiparallel beta sheets, which pack against each other. Both beta sheets contribute conserved hydrophobic residues to a compact core. The topology is more similar to that of domain 2 of CD4, PapD, and the extracellular domain of the human growth hormone receptor than to that of immunoglobulin C domains. The module contains an Arg-Gly-Asp sequence known to be involved in cell adhesion. This tripeptide is solvent exposed and lies on a conformationally mobile loop between strands F and G, consistent with its cell adhesion function.

Amino Acid Sequence↗
PubMed1992

Solution structure of the fibrin binding finger domain of tissue-type plasminogen activator determined by 1H nuclear magnetic resonance.

The amino acid sequence of the first domain of tissue-type plasminogen activator (t-PA) includes eight residues that are highly conserved in the type 1 finger domains found in human fibronectin. A construct comprising 50 residues from this finger domain of t-PA has been expressed and its solution structure has been determined by two-dimensional nuclear magnetic resonance spectroscopy. A total of 782 experimental restraints consisting of 723 interproton distances derived from nuclear Overhauser effect measurements, 43 torsion angles, and 16 hydrogen bond restraints were used as the input for dynamical simulated annealing structure calculations. Twenty-eight structures were obtained that satisfied the experimental data with no single distance violation greater than 0.3 A. The average atomic root-mean-square distribution for the backbone atoms of the final structures was 0.41 (+/- 0.13) A for the well defined part of the structure (residues 4 to 47). The overall fold of the t-PA finger domain shows a striking similarity to that of the seventh type 1 repeat of human fibronectin with the side-chains of conserved residues lying in similar conformations. One significant difference between the two molecules is that hydrophobic residues cover the exposed surface of the principal beta-sheet region in the t-PA finger domain. It is suggested that one face of this region may interact with parts of the complete t-PA protein.

Amino Acid Sequence↗
PubMed1992

A selectable bifunctional beta-galactosidase::phleomycin-resistance fusion protein as a potential marker for eukaryotic cells.

The Sh ble gene, conferring phleomycin resistance (PhR), was fused in frame to both the 3' and 5' ends of the Escherichia coli lacZ gene. The bifunctionality of the resulting 130-kDa hybrid proteins was demonstrated in E. coli and in the fungus, Tolypocladium geodes. PhR transformants of both organisms could be selected for. All transformants from E. coli and most from T. geodes displayed beta Gal activity. In the fungal host, higher transformation frequencies and greater levels of beta Gal activity were observed in clones harboring the lacZ::Sh ble fusion, as compared to the Sh ble::lacZ configuration. This system appears to be a potentially useful tool for the direct selection of transformants, and the evaluation of gene expression and regulation in a wide variety of prokaryotic and eukaryotic hosts.

Amino Acid Sequence↗
PubMed1992

1H NMR assignment and secondary structure of the cell adhesion type III module of fibronectin.

The secondary structure of the tenth type III module from human fibronectin has been determined using NMR. This type of module appears many times in a wide variety of proteins. The type III module described here contains an Arg-Gly-Asp sequence known to be involved in cell-cell adhesion. The module was expressed in yeast and characterized by amino acid sequencing and mass spectrometry. 2D and 3D NMR spectroscopy of 15N-labeled protein was used to perform sequence-specific assignment of the spectrum. The secondary structure was defined by patterns of nuclear Overhauser effects, 3JNH-alpha CH spin-spin coupling constants, and amide proton solvent exchange rates. The molecule consists of seven beta-strands in two antiparallel beta-sheets with an immunoglobulin-like fold similar to that predicted for homologous modules in the cytokine receptor super family [Bazan, J. F. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 6934-6938]. The Arg-Gly-Asp sequence is located on a loop between the beta-strands F and G.

Amino Acid Sequence↗
PubMed1992

The three-dimensional structure of the first EGF-like module of human factor IX: comparison with EGF and TGF-alpha.

The three-dimensional structure of the first epidermal growth factor (EGF)-like module from human factor IX has been determined in solution using two-dimensional nuclear magnetic resonance (in the absence of calcium and at pH 4.5). The structure was found to resemble closely that of EGF and the homologous transforming growth factor-alpha (TGF-alpha). Residues 60-65 form an antiparallel beta-sheet with residues 68-73. In the C-terminal subdomain a type II beta-turn is found between residues 74 and 77 and a five-residue turn is found between residues 79 and 83. Glu 78 and Leu 84 pair in an antiparallel beta-sheet conformation. In the N-terminal region a loop is found between residues 50 and 55 such that the side chains of both are positioned above the face of the beta-sheet. Residues 56-60 form a turn that leads into the first strand of the beta-sheet. Whereas the global fold closely resembles that of EGF, the N-terminal residues of the module (46-49) do not form a beta-strand but are ill-defined in the structure, probably due to the local flexibility of this region. The structure is discussed with reference to recent site-directed mutagenesis data, which have identified certain conserved residues as ligands for calcium.

Amino Acid Sequence↗
PubMed1992

Efficient secretion of human lysozyme fused to the Sh ble phleomycin resistance protein by the fungus Tolypocladium geodes.

Tolypocladium geodes strain NC50 was transformed by different integrating vectors bearing both a synthetic gene encoding human lysozyme (HLz) and the Sh ble phleomycin resistance marker, either in separate expression cassettes or in transcriptional or translational fusion configurations. Clones derived from all vectors were able to secrete HLz. The highest productivities in shake flasks (up to 150 mg l-1 in 5 days) were obtained when HLz was fused at the C-terminal end of the Sh ble protein. The fusion protein is efficiently secreted and release of active lysozyme occurs by extracellular proteolytic cleavage in the junction peptide.

Amino Acid Sequence↗
PubMed1992

Ligand requirements for Ca2+ binding to EGF-like domains.

Site-specific mutagenesis studies of the first epidermal growth factor-like (EGF-like) domain of human clotting factor IX suggest that the calcium-binding site present in this domain (dissociation constant Kd = 1.8 mM at pH 7.5 and ionic strength I = 0.15) involved the carboxylate residues Asp47, Asp49 and Asp64. To further characterize the ligands required for calcium binding to EGF-like domains, two new mutations, Asp47----Asn and Asp49----Asn, were introduced into the domain by peptide synthesis. 1H-NMR spectroscopy was used to obtain the dissociation constants for calcium binding to these mutations. Calcium binding to the Asp49----Asn modified domain is only mildly affected (Kd = 6 mM, I = 0.15), whereas binding to the Asp47----Asn modified domain is severely reduced (Kd = 42 mM, I = 0.15). From these data, it is proposed that the anionic oxygen atoms of the side chains of residues 47 and 64 are essential for calcium binding, whereas the side chain ligand for calcium at residue 49 can be a carboxyamide oxygen. As a control, the introduction of the modification Glu78----Asp in a region of the domain not believed to be involved in calcium binding had very little effect on the Kd for calcium (Kd = 2.6 mM, I = 0.15). Finally, the effect of an Asp47----Gly substitution found in the natural haemophilia B mutant, factor IXAlabama, was investigated. This peptide has a markedly reduced affinity for calcium (Kd = 37 mM, I = 0.15), suggesting that the defect in factor IXAlabama is due to impaired calcium binding to its first EGF-like domain.

Amino Acid Sequence↗
PubMed1992

Positive and negative symptoms. Relation to familial transmission of schizophrenia.

The authors assessed the relevance of clinical symptoms to genetic research in schizophrenia in the nuclear families of 65 chronic schizophrenic probands. The morbidity risk for schizophrenia and schizotypal personality (a 'spectrum' disorder) was markedly reduced in first-degree relatives of probands with predominant negative symptoms, as compared with relatives of probands with other symptom patterns. The data support the notion that negative-symptom schizophrenia has an attenuated genetic component.

Adult↗
PubMed1992

Mortality in systemic sclerosis (scleroderma).

Two hundred and thirty-seven patients with systemic sclerosis were followed prospectively in a scleroderma clinic. The overall 3, 6, and 9-year survival rates were 86, 76 and 61 per cent respectively. Renal, cardiac and pulmonary disease, and older age at enrollment were adverse prognostic factors associated with reduced survival. There were no significant differences in survival between males and females or in patients with restricted compared to those with diffuse skin thickening. Death from systemic sclerosis was most frequently due to pulmonary hypertension, with fewer than expected deaths from renal or cardiac causes. Twenty-eight per cent of deaths were due to causes unrelated to systemic sclerosis, most commonly cancer and ischaemic heart disease, and in older patients.

Coronary Disease↗
PubMed1991

Three-dimensional structure of a complement control protein module in solution.

The complement control protein (CCP) modules (also known as short consensus repeats) are defined by a consensus sequence within a stretch of about 60 amino acid residues. These modules have been identified more than 140 times in over 20 proteins, including 12 proteins of the complement system. The solution structure of the 16th CCP module from human complement factor H has been determined by a combination of 2-dimensional nuclear magnetic resonance spectroscopy and restrained simulated annealing. In all, 548 structurally important nuclear Overhauser enhancement cross-peaks were quantified as distance restraints and, together with 41 experimentally measured angle restraints, were incorporated into a simulated annealing protocol to determine a family of closely related structures that satisfied the experimental observations. The CCP structure is shown to be based on a beta-sandwich arrangement; one face made up of three beta-strands hydrogen-bonded to form a triple-stranded region at its centre and the other face formed from two separate beta-strands. Both faces of the molecule contribute highly conserved hydrophobic side-chains to a compact core. The regions between the beta-strands are composed of both well-defined turns and less well-defined loops. Analysis of CCP sequence alignments, in light of the determined structure, reveals a high degree of conservation amongst residues of obvious structural importance, while almost all insertions, deletions or replacements observed in the known sequences are found in the less well-defined loop regions. On the basis of these observations it is postulated that models of other CCP modules that are based on the structure presented here will be accurate. Certain families of CCP modules differ from the consensus in that they contain extra cysteine residues. As a test of structural consensus, the extra disulphide bridges are shown to be easily accommodated within the determined CCP model.

Amino Acid Sequence↗
PubMed1991

The structure and function of protein modules.

Analysis of protein sequences shows that many proteins in multicellular organisms have evolved by a process of exon shuffling, deletion and duplication. These exons often correspond to autonomously folding protein modules. Many extracellular enzymes have this modular structure; for example, serine proteases involved in blood-clotting, fibrinolysis and complement. The main role of these modules is to confer specificity by protein-protein interactions. Lack of structural information about such proteins has required a new strategy for studying the structure and function of protein modules. The strategy involves the production of individual modules by protein expression techniques, determination of their structure by high resolution nuclear magnetic resonance and definition of functional patches on the modules by site-directed mutagenesis and biological assays. The structures of the growth factor module, the fibronectin type 1 module and the complement module are briefly described. The possible functional roles of modules in various proteins, including the enzymes factor IX and tissue plasminogen activator, are discussed.

Amino Acid Sequence↗
PubMed1991

Key residues involved in calcium-binding motifs in EGF-like domains.

Many extracellular proteins with diverse functions contain domains similar to epidermal growth factor (EGF), a number of which have a consensus Asp/Asn, Asp/Asn, Asp*/Asn*, Tyr/Phe (where the asterisk denotes a beta-hydroxylated residue). These include the coagulation factors IX and X, proteins with two EGF-like domains, the first of which contains the consensus residues. The first EGF-like domain of human factor IX contains a calcium-binding site, which is believed to be responsible for one of the high-affinity sites detected in this protein. Similar results have been obtained for bovine factor X. We have now used protein engineering and 1H-NMR techniques to investigate the importance of individual consensus residues for ligand binding. Measurement of a calcium-dependent Tyr 69 shift in the isolated first EGF-like domain from human factor IX demonstrates that Asp 47, Asp 49, and Asp 64 are directly involved in this binding. Gln 50, whose importance has previously been overlooked, is also involved in this binding. Two mutations in this domain, Asp 47----Glu, and Asp 64----Asn, present in patients with haemophilia B, reduce calcium binding to the domain greater than 4-fold and greater than 1,000-fold, respectively. Furthermore, the defective calcium binding of Asn 64 can be partially rescued by the compensatory mutation Gln 50----Glu. This latter mutation, when introduced singly more than doubles the affinity of the domain for calcium. This study thus defines residues involved in a new type of calcium-binding site and provides strong circumstantial evidence for calcium-binding motifs in many extracellular proteins, including the developmentally important proteins of Drosophila, notch, delta and crumbs.

Amino Acid Sequence↗
PubMed1991

Secondary structure of a complement control protein module by two-dimensional 1H NMR.

The complement control protein (CCP) module (also known as the short consensus repeat) is a consensus sequence of about 60 amino acid residues which is thought to fold independently. It occurs over 140 times in more than 20 extracellular mosaic proteins including 12 proteins of the complement cascade. An isolated CCP module, the 16th repeat from human complement factor H, has been expressed in a yeast vector and shown to fold with the same pattern of disulfide bond formation as is seen in the native protein. Two-dimensional 600-MHz 1H NMR spectra of this module have been recorded at pH 3.3 and 6.0 and analyzed to permit determination of secondary structure in solution. The CCP module comprises two predominantly extended segments (Glu1-His13 and Ala17-Glu27), two segments of double-stranded antiparallel beta-sheet (Gly14-Val16 paired with Tyr31-Cys33 and Gly38-Asp40 paired with Ser57-Ile59), and a short piece of triple-stranded beta-sheet (Glu27-Thr30, Ile44-Leu48, and Lys51-Ser53). Turns occur at Asp22, Gly36, and Glu50, while Gly41-Ala43 appear to form a looped-out segment or bulge. This structure is compared with a secondary structure prediction made on the basis of an alignment scheme of 101 sequences for CCP modules [Perkins, S. J., Haris, P. I., Sim, R. B., & Chapman, D. (1988) Biochemistry 27, 4004-4012]--the experimentally determined secondary structure bears an overall resemblance to the predicted one but differs in the number and position of turns. Some of those amino acid residues which are highly conserved throughout the range of CCP modules appear to play a role in stabilizing the global fold.

Amino Acid Sequence↗
PubMed1991

Protein modules.

As the database of protein sequences grows it is becoming apparent that many proteins are constructed from relatively few modular units that appear many times. Determination of the three-dimensional structure of such modules by NMR has been possible due to their production in relatively large quantities by recombinant DNA techniques. The knowledge gained about the structure of individual modules can then be used to predict their properties in a variety of intact proteins.

Amino Acid Sequence↗