Infrared spectral studies of metal binding effects on the secondary structure of bean plastocyanin

Hare, Jeffrey W.; Solomon, Edward I.; Gray, Harry B.

doi:10.1021/ja00427a025

Cited by 19 publications

(13 citation statements)

References 2 publications

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“…If this single shell does not adequately describe the EXAFS, then a second shell is added. Experience has shown that up to four or so different shells may be fit to good data on a k range of [4][5][6][7][8][9][10][11][12] A-' before correlation problems become so severe as to render the results unreliable. The type of scatterer atom chosen for a given shell can be tested by using the pairwise phase parameters for a different scatterer type.…”

Section: Resultsmentioning

confidence: 99%

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Characterization of the blue copper site in oxidized azurin by extended x-ray absorption fine structure: Determination of a short Cu—S distance

Tullius

Frank

Hodgson

1978

Proc. Natl. Acad. Sci. U.S.A.

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The primary coordination environment of the "blue" copper ion in oxidized azurin has been elucidated by x-ray absorption spectroscopy. The most striking-feature is the unambiguous presence of a very short copper-sulfur, distance at 2.10 + 0.02 A. Nitrogen ligands, presumed to be from imidazoles, are found at 1.97 A. There is some evidence that the copper coordination sphere may be completed by a second sulfur, the distance of which is determined with much less certainty.Proteins that contain the "blue" (or type 1) copper site (1) have long offered a challenge to chemists to explain their unique spectroscopic and redox properties. Some of the basic aspects of the structure of such blue sites have already become clear, as revealed by interpretation of several types of spectroscopic data. The model for the blue site of bean plastocyanin put forth by Gray and coworkers (2) is probably the best distillation of current spectroscopic and chemical information on blue copper. The ligand field spectrum implies a distorted tetrahedral coordination of the copper, which is also reasonable when the high redox potential of the copper is considered. A thiolate sulfur from cysteine is proposed as one of the metal ligands. Two imidazole nitrogens from histidines are also implicated as ligands, from NMR studies (3-5). The fourth ligand of copper is less certain. A deprotonated peptide nitrogen from the protein has been proposed as this ligand (6), but methionine sulfur now seems to be the most likely possibility. The x-ray protein structure of poplar plastocyanin has recently been solved to 2.7 A resolution (7). The copper in this plastocyanin is coordinated by cysteinate, two imidazoles, and methionine.The availability of even a high-resolution x-ray crystallographic structure of a blue protein would not necessarily explain all of the unusual spectroscopic and redox properties of blue copper. Subtle changes in bond distance and coordination geometry, which the limited accuracy of even a good protein crystal structure might render difficult to resolve, can be expected to have major effects on these properties.A technique that has been recently used to examine the environment of a selected element in a complex macromolecular system is x-ray absorption spectroscopy. The fine structure that occurs at energies above the x-ray absorption edge (called EXAFS) provides a way of determining distances, numbers, and h-ypes of ligands coordinating a metal. Since the EXAFS method does not require crystalline samples, it can be applied to the study of metalloproteins under noncrystalline or physiological conditions (8)(9)(10)(11). In contrast to macromolecular crystallographic results, where it is difficult to obtain high accuracy except in the few cases of very well refined structures, EXAFS can provide accurate metal-to-ligand distances (12). Coupled with the element-selective nature of the measurements, the EXAFS technique is ideal for investigating the environment of a specific metal ion in a protein.In order to further elucidate t...

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Section: Resultsmentioning

confidence: 99%

“…The fourth ligand of copper is less certain. A deprotonated peptide nitrogen from the protein has been proposed as this ligand (6), but methionine sulfur now seems to be the most likely possibility. The x-ray protein structure of poplar plastocyanin has recently been solved to 2.7 A resolution (7).…”

mentioning

confidence: 99%

Characterization of the blue copper site in oxidized azurin by extended x-ray absorption fine structure: Determination of a short Cu—S distance

Tullius

Frank

Hodgson

1978

Proc. Natl. Acad. Sci. U.S.A.

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“…It is reasonable to assume therefore, that the analogous two residues in the bean protein (28), His-38 and His-88, are also ligands. The fourth ligand in the proposed donor set for bean plastocyanin has been identified in extensive infrared spectral studies (29). These experiments have revealed that a short section of ahelix in apoplastocyanin is strongly perturbed upon metal [Cu(II) or Co(II)] incorporation.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic studies and a structural model for blue copper centers in proteins.

Solomon¹,

Hare²,

Gray³

1976

Proc. Natl. Acad. Sci. U.S.A.

162

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Distorted tetrahedral Cu(II) should exhibit d-d transitions well below 10,000 cm1, assuming that the ligand field is not unusually strong. We have undertaken, therefore, a detailed investigation of the near-infrared absorption, CD, and magnetic circular dichroism (MCD) spectra of stellacyanin, plastocyanin, and azurin. Detailed analysis of these and analogous visible spectral data has allowed assignments to be made of both the d-d and charge transfer transitions. Interpretation of the charge transfer spectra has been aided further by the identification of the probable ligands of Cu(II) in bean plastocyanin. MATERIALS AND METHODSFrench bean plastocyanin (Phaseolus vulgaris) (18), azurin (Pseudomonas aeruginosa) (19), and stellacyanin (Rhus vernicifera) (20) were purified by standard methods. Near-infrared spectra were obtained on protein films to minimize interference by water absorption and permit a wide variation of temperature. The protein solutions were dialyzed against deionized distilled water and concentrated, first by pressurized membrane ultrafiltration and then, by placing drops on a plexiglas disk in a metal dessicator over Drierite. After three of four drops had been successively concentrated (ten to fifteen for the thick films), the film was prepared'by transferring the disk to a dessicator containing a saturated potassium acetate solution. This controlled humidity allowed the film to form slowly, thereby preventing most of the cracking caused by rapid removal of excess water. The drying process was halted by transfer of the film to a dessicator charged with a saturated sodium hydrogen phosphate solution.The near-infrared CD and MCD spectra were obtained with samples run in deuterated phosphate buffer in order to extend the spectral range to about 1850 nm. Although the infrared overtones of water do not give rise to a measureable CD spectrum, an absorbance of 1.0 or greater diminished the light level to the limit of detector response. The deuterated protein solutions were prepared by evaporating unbuffered, concentrated aqueous solutions in a Drierite dessicator as described above. The films were then transferred to a

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“…In proteins, the peptide bonds -CO-NH-have several distinct vibrational modes, usually expressed as amide I, II, III, IV, V, VI, VII, A, and B bands (42,43). Based on the given infrared absorption bands characteristic of polypeptides and proteins including some enzymes (35,36,38,42), the assignment of different bands of the free and immobilized tyrosinase protein are summarized in Table 1.…”

Section: Ftir Analysismentioning

confidence: 99%

Formation of Protein–Birnessite Complex: XRD, FTIR, and AFM Analysis

Naidja

Liu

Huang

2002

Journal of Colloid and Interface Science

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Infrared spectral studies of metal binding effects on the secondary structure of bean plastocyanin

Cited by 19 publications

References 2 publications

Characterization of the blue copper site in oxidized azurin by extended x-ray absorption fine structure: Determination of a short Cu—S distance

Characterization of the blue copper site in oxidized azurin by extended x-ray absorption fine structure: Determination of a short Cu—S distance

Spectroscopic studies and a structural model for blue copper centers in proteins.

Formation of Protein–Birnessite Complex: XRD, FTIR, and AFM Analysis

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