1H-n.m.r. investigation of the interaction between cytochrome c and cytochrome b5.

The interaction between eukaryotic cytochrome c and the tryptic fragment of bovine liver microsomal cytochrome b5 was studied by 1H-n.m.r. spectroscopy, and a procedure was developed that may be generally applicable to the study of macromolecular interactions by n.m.r. At pH6.3 (27 degrees C, I approx. 0.04) the two ferricytochromes were found to form a 1:1 complex with an association constant of approx. 10(3) M -1. The protein--protein-interaction region was found to encompass the region of the surface of horse cytochrome c that includes Ile-81, Phe-82, Ala-83 and Ile-85, and Lys-13 and Lys-72 of horse cytochrome c were suggested to be involved in two important intermolecular interactions. Me3Lys-72 of Candida krusei cytochrome c was shown to be involved in the interaction.     

1H-n.m.r. studies of squash seed trypsin inhibitor

1H-n.m.r. studies at 500 MHz have been performed on a trypsin inhibitor (CMTI-III) found in squash seed (Cucurbita maxima). The sequential resonance assignments have been made using two-dimensional techniques. The chemical shifts for the assigned protons are reported at 30 degrees, pH 2.8 and form a basis for the determination of the solution structure of CMTI-III. Analysis of the NOE data, NH-alpha CH vicinal coupling constants and pattern of slowly exchanging amide protons indicates that the predominant feature of the solution conformation is a triple stranded beta sheet consisting of residues 8-10, 21-23, and 26-29. Residues 12-15 appear to form a beta turn.     

1H-n.m.r. investigation of naturally occurring and chemically oversulphated dermatan sulphates. Identification of minor monosaccharide residues.

The 1H-n.m.r. spectra of various dermatan sulphate preparations present, besides the major signals of the basic disaccharide unit, several other minor signals. We have assigned most of them by n.m.r., using two-dimensional proton-proton double-quantum-correlation and nuclear-Overhauser-effect spectroscopy experiments. This allowed us to identify 2-O-sulphated L-iduronic acid and D-glucuronic acid residues as well as 6-sulphated N-acetylgalactosamine (presumably 4-O-sulphated as well). 2-O-Sulphated iduronic acid was present to similar extents (6-10% of total uronic acids) in pig skin dermatan sulphate and pig intestine dermatan sulphate, whereas glucuronic acid represented 17% of the uronic acid of pig skin dermatan sulphate and was virtually absent (1%) from the other preparation. 6-O-Sulphated N-acetylgalactosamine was present in minor amounts in pig intestine dermatan sulphate only. The influence of sulphation of iduronic acid units on their conformation was assessed by using chemically oversulphated pig intestine dermatan sulphate. Introduction of sulphate groups in this unit in dermatan sulphate tends to shift the conformational equilibrium towards the 1C4 conformer.     

A 2D-1H-n.m.r. study of some Shigella flexneri O-polysaccharides

A 1H-n.m.r. study of the O-polysaccharides from different types of Shigella flexneri has been performed. With the aid of 2D-n.m.r. techniques, namely, J-resolved, spin-spin correlation, and NOESY experiments, most of the structural features of these polysaccharides could be deduced. Sequences could generally be obtained from the NOESY experiments. When using a prolonged mixing time in these experiments, cross-peaks due to spin diffusion from one anomeric proton to the anomeric proton of an adjacent residue could be obtained, thereby giving complementary sequence information.     

Conformational studies on gastrin related peptides by high resolution 1H-n.m.r

The secondary structures of three gastrin analogs, HC1 X H-Trp-Nle-Asp(O-tBu)-Phe-NH2 (tetragastrin), pGlu-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2 (octagastrin), and H-Leu-(Glu)5-Ala-Tyr-Gly-Trp-Nle-Asp-Phe-NH2 (minigastrin) were studied by 1H-n.m.r. in dimethylsulfoxide and in trifluoroethanol. All three compounds were found to assume a random conformation in the former solvent, while some ordered secondary structure is present in trifluoroethanol even at the tetrapeptide level. This was shown by temperature studies and solvent titrations. At least four amide protons were found to be solvent shielded in the longer hormone.     

Polydepsipeptides. 13. Synthesis and 1H-n.m.r. analysis of collagen model structures

The synthesis of three collagen model analogs is described: Ac-Ala-Gly-Pro-Ala-Gly-Pro-NHMe, Ac-Ala-Gly-Pro-Ala-Glc-Pro-NHMe, and Ac-Ala-Glc-Pro-Ala-Gly-Pro-NHMe, where Glc stands for glycolic acid. The 1H-n.m.r. properties of these compounds in dimethylsulfoxide-d6 and trifluoroethanol are described. While in DMSO-d6 the compounds are random, in TFE the glycine amide protons seem to be less solvent exposed than the other amide protons. Little difference was found in the behavior of the three compounds.     

1H-n.m.r. studies of the isolated activation segment from pig procarboxypeptidase A.

The isolated activation segment (asA) from pig pancreatic procarboxypeptidase A was studied by 1H-n.m.r. spectroscopy over a wide range of solution conditions. Isolated asA shows many characteristics of compactly folded globular proteins, such as the observation of perturbed positions for resonances from methyl groups, alpha-carbon atoms, histidine residues and the tyrosine residue. The single tyrosine residue (Tyr-70) exhibits a very high pKa, and both histidine and tyrosine residues show slow chemical modification (deuteration and iodination). In contrast, asA shows rapid NH exchange. Analysis of the spectra by pH titration and nuclear Overhauser effects revealed several residue interactions. Quantitative analysis of deuterium and tritium exchange allowed the assignment of the histidine C-2-H resonances to their respective residues in the sequence. His-66, the closest to the sites of proteolytic attack in the proenzyme, is shown to be the most accessible to solvent in procarboxypeptidase A. It was also shown that asA is thermally very stable ['melting' temperature (Tm) 88 degrees C] and requires a high urea concentration for denaturation (6.25 M, at pH 7.5). Evidence is presented for some degree of conformational flexibility in the premelting range, a feature that could be ascribed to the preponderance of helical secondary structure and to the lack of disulphide bridges. The free solution structure of asA is probably unchanged when it binds to carboxypeptidase A.     

Two-dimensional, 1H-n.m.r. study of peracetylated, reduced derivatives of three oligosaccharides isolated from human milk

The structures of the peracetylated derivatives of the following alditols obtained from oligosaccharides of human milk have been established by two-dimensional, J-resolved and J-correlated, ¹H-n.m.r. spectroscopy at 360 MHz: β- d-Galp-(1→3)-β- d-GlcpNAc-(1→3)-β- d-Galp-(1→4)- d-Glc-ol, α- l-Fucp-(1→2)-β- d-Galp-(1→3)-β- d-GlcpNAc-(1→3)-β- d-Galp-(1→4)- d-Glc-ol, and β- d-Galp-(1→3)-β- d-GlcpNAc-(1→3)-[β- d-Galp-(1→4)-β- d-GlcpNAc-(1→6)]-β- d-Galp-(1→4)- d-Glc-ol.     

Controlled proteolysis of mouse epidermal growth factor. An RP-HPLC and 1H-n.m.r. study

Tryptic digestion of the mouse epidermal growth factor (mEGF) and the chromatographic separation of its proteolytic fragments by RP-HPLC affords the isolation of the pure hormone, of its 1-48 (Des(49-53)mEGF) and 1-45 (Des(46-53)mEGF) derivatives, and of the carboxyl-terminal pentapeptide W49-W50-E51-L52-R53. Kinetics of mEGF proteolytic degradation follows a two-state time-course: native mEGF being converted into Des(49-53)mEGF with an apparent half-time of 10 min; and Des(49-53)mEGF subsequently hydrolyzed to Des(46-53)mEGF with an apparent half-time of 7 h. Native mEGF and its proteolytic fragments have been characterized by 1H-n.m.r. spectroscopy. In the aromatic and aliphatic regions, the 1H-n.m.r. spectrum proved to be a sufficiently sensitive probe for following controlled proteolysis, and for analyzing the influence of the carboxyl-terminal sequence on the hormone conformation and stability.     

1H- and 2H-n.m.r. studies of water in gamma-irradiated phosphatidylcholine multilamellar liposomes

1H- and 2H-n.m.r. studies of gamma-irradiation-induced variations in the dynamic structure and proportional amounts of free, trapped and bound water species in multilamellar liposomes are reported and discussed. Bound water is shown to increase with dose and to be present in two different structural states. A dose-dependent decrease in the 1H-n.m.r. relaxation times of bound water following gamma-irradiation is reported. Variations are suggested as being due to large scale changes at the bilayer surface.     

1H-n.m.r. evaluation of the ferricytochrome c-cardiolipin interaction. Effect of superoxide radicals.

The interaction between ferricytochrome c and cardiolipin was investigated by 1H n.m.r. at 270 MHz. From the phospholipid-induced changes of the protein spectral features it is concluded that the first 2 equivalents of cardiolipin cause a conformational change at the lower part of the solvent-exposed haem edge, involving a rearrangement of the hydrogen-bond interactions of propionate 6, thus partly accounting for the lowered redox potential of cytochrome c in the presence of cardiolipin. The increased value for the pK of the alkaline isomerization of ferricytochrome c shows that cardiolipin stabilizes the native structure of the protein, indicating that the oxidized form assumes ferrocytochrome c-like properties. Peroxidation of cardiolipin by superoxide radical ions drastically decreases the protein binding to this phospholipid. The implications of this finding, and the likelihood of the ternary cytochrome c-cardiolipin-cytochrome c oxidase complex, for the binding of cytochrome c to cytochrome c oxidase in vivo, are discussed in relation to peroxidative damage following ischaemia and reperfusion.     

Domain structure and 1H-n.m.r. spectroscopy of the pyruvate dehydrogenase complex of Bacillus stearothermophilus.

The pyruvate dehydrogenase complex of Bacillus stearothermophilus was treated with Staphylococcus aureus V8 proteinase, causing cleavage of the dihydrolipoamide acetyltransferase polypeptide chain (apparent Mr 57 000), inhibition of the enzymic activity and disassembly of the complex. Fragments of the dihydrolipoamide acetyltransferase chains with apparent Mr 28 000, which contained the acetyltransferase activity, remained assembled as a particle ascribed the role of an inner core of the complex. The lipoic acid residue of each dihydrolipoamide acetyltransferase chain was found as part of a small but stable domain that, unlike free lipoamide, was able still to function as a substrate for reductive acetylation by pyruvate in the presence of intact enzyme complex or isolated pyruvate dehydrogenase (lipoamide) component. The lipoyl domain was acidic and had an apparent Mr of 6500 (by sedimentation equilibrium), 7800 (by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis) and 10 000 and 20 400 (by gel filtration in the presence and in the absence respectively of 6M-guanidinium chloride). 1H-n.m.r. spectroscopy of the dihydrolipoamide acetyltransferase inner core demonstrated that it did not contain the segments of highly mobile polypeptide chain found in the pyruvate dehydrogenase complex. 1H-n.m.r. spectroscopy of the lipoyl domain demonstrated that it had a stable and defined tertiary structure. From these and other experiments, a model of the dihydrolipoamide acetyltransferase chain is proposed in which the small, folded, lipoyl domain comprises the N-terminal region, and the large, folded, core-forming domain that contains the acetyltransferase active site comprises the C-terminal region. These two regions are separated by a third segment of the chain, which includes a substantial region of polypeptide chain that enjoys high conformational mobility and facilitates movement of the lipoyl domain between the various active sites in the enzyme complex.     

Sequence-specific 1H-n.m.r. assignments and peptide backbone conformation in rat epidermal growth factor.

The solution conformation of rat epidermal growth factor (EGF) has been investigated by proton n.m.r. techniques. Two-dimensional proton n.m.r. experiments have allowed sequential resonance assignments to be made for most protons. On the basis of these assignments, two regions of anti-parallel beta-sheet structure have been derived from the n.m.r. data. A beta-sheet segment running from about V19 to V23 (capital letters refer to amino acids in the single-letter notation) is folded onto a beta-sheet segment running from R28 to N32 and joined by a chain reversal from E24 to D27. A second region involves a beta-turn from V34 to Y37, which starts a short beta-sheet up to G39, followed by a chain reversal up to Q43, which leads to folding of the C-terminal beta-sheet segment, i.e. H44-R45, running antiparallel to the short Y37 beta-sheet segment. The N-terminal segment up to G18 exists in a multiple bend conformation and is folded on to the V29-V23/R28-N32 beta-sheet such that Y10, Y13, Y22 and Y29 are proximal to each other. Structural comparison of rat, murine and human EGFs indicates a number of highly conserved structural features common to at least these species of EGF.