Regio-selective detection of dynamic structure of transmembrane alpha-helices as revealed from (13)C NMR spectra of [3-13C]Ala-labeled bacteriorhodopsin in the presence of Mn2+ ion

13C Nuclear magnetic resonance (NMR) spectra of [3-(13)C]Ala-labeled bacteriorhodopsin (bR) were edited to give rise to regio-selective signals from hydrophobic transmembrane alpha-helices by using NMR relaxation reagent, Mn(2+) ion. As a result of selective suppression of (13)C NMR signals from the surfaces in the presence of Mn(2+) ions, several (13)C NMR signals of Ala residues in the transmembrane alpha-helices were identified on the basis of site-directed mutagenesis without overlaps from (13)C NMR signals of residues located near the bilayer surfaces. The upper bound of the interatomic distances between (13)C nucleus in bR and Mn(2+) ions bound to the hydrophilic surface to cause suppressed peaks by the presence of Mn(2+) ion was estimated as 8.7 A to result in the signal broadening to 100 Hz and consistent with the data based on experimental finding. The Ala C(beta) (13)C NMR peaks corresponding to Ala-51, Ala-53, Ala-81, Ala-84, and Ala-215 located around the extracellular half of the proton channel and Ala-184 located at the kink in the helix F were successfully identified on the basis of (13)C NMR spectra of bR in the presence of Mn(2+) ion and site-directed replacement of Ala by Gly or Val. Utilizing these peaks as probes to observe local structure in the transmembrane alpha-helices, dynamic conformation of the extracellular half of bR at ambient temperature was examined, and the local structures of Ala-215 and 184 were compared with those elucidated at low temperature. Conformational changes in the transmembrane alpha-helices induced in D85N and E204Q and its long-range transmission from the proton release site to the site around the Schiff base in E204Q were also examined.

Cytoplasmic surface structure of bacteriorhodopsin consisting of interhelical loops and C-terminal alpha helix, modified by a variety of environmental factors as studied by (13)C-NMR

We have examined the (13)C-NMR spectra of [3-(13)C] Ala-labeled bacteriorhodopsin and its mutants by varying a variety of environmental or intrinsic factors such as ionic strength, temperature, pH, truncation of the C-terminal alpha helix, and site-directed mutation at cytoplasmic loops, in order to gain insight into a plausible surface structure arising from the C-terminal alpha helix and loops. It is found that the surface structure can be characterized as a complex stabilized by salt bridges or metal-mediated linkages among charged side chains. The surface complex in bacteriorhodopsin is most pronounced under the conditions of 10 mM NaCl at neutral pH but is destabilized to yield relaxed states when environmental factors are changed to high ionic strength, low pH and higher temperature. These two states were readily distinguished by associated spectral changes, including suppressed (cross polarization-magic angle spinning NMR) or displaced (upfield) (13)C signals from the C-terminal alpha helix, or modified spectral features in the loop region. It is also noteworthy that such spectral changes, when going from the complexed to relaxed states, occur either when the C-terminal alpha helix is deleted or site-directed mutations were introduced at a cytoplasmic loop. These observations clearly emphasize that organization of the cytoplasmic surface complex is important in the stabilization of the three-dimensional structure at ambient temperature, and subsequently plays an essential role in biological functions.

Surface dynamics of bacteriorhodopsin as revealed by (13)C NMR studies on [(13)C]Ala-labeled proteins: detection of millisecond or microsecond motions in interhelical loops and C-terminal alpha-helix

We have recorded (13)C NMR spectra of [2-(13)C]-, [1-(13)C]-, [3-(13)C],- and [1,2,3-(13)C(3)]Ala-labeled bacteriorhodopsin (bR), and its mutants, A196G, A160G, and A103C, by means of cross polarization-magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) techniques, to reveal the conformation and dynamics of bR, with emphasis on the loop and C-terminus structures. The (13)C NMR signals of the loop (C-D, E-F, and F-G) regions were almost completely suppressed from [2-(13)C]-, [1-(13)C]Ala-, and [1-(13)C]Gly-labeled bR, due to the presence of conformational fluctuation with correlation times of 10(-4) s that interfered with the peak-narrowing by magic angle spinning. The observation of such suppressed peaks for specific residues provides a unique means of detecting intermediate frequency motions on the time scale of ms or micros in the surface loops of membrane proteins. Instead, the three well-resolved (13)C CP-MAS NMR signals of [2-(13)C]Ala-bR, at 50.38, 49.90, and 47.96 ppm, were ascribed to the C-terminal alpha-helix previously proposed from the data for [3-(13)C]Ala-bR: the former two peaks were assigned to Ala 232 and 238, in view of the results of successive proteolysis experiments, while the highest-field peak was ascribed to Ala 235 prior to Pro 236. Even such (13)C NMR signals were substantially broadened when (13)C NMR spectra of fully labeled [1,2,3-(13)C]Ala-bR were recorded, because the broadening and splitting of peaks due to the accelerated transverse relaxation rate caused by the increased number of relaxation pathways through a number of (13)C-(13)C homo-nuclear dipolar interactions and scalar J couplings, respectively, are dominant among (13)C-labeled nuclei. In addition, approximate correlation times for local conformational fluctuations of different domains, including the C-terminal tail, C-terminal alpha-helix, loops, and transmembrane alpha-helices, were estimated by measurement of the spin-lattice relaxation times in the laboratory frame and spin-spin relaxation times under the conditions of cross-polarization-magic angle spinning, and comparative study of suppressed specific peaks between the CP-MAS and DD-MAS experiments.

A (13)C NMR study on [3-(13)C]-, [1-(13)C]Ala-, or [1-(13)C]Val-labeled transmembrane peptides of bacteriorhodopsin in lipid bilayers: insertion, rigid-body motions, and local conformational fluctuations at ambient temperature

We have recorded (13)C NMR spectra of selectively [3-(13)C]Ala-, [1-(13)C]Ala-, or [1-(13)C]Val-labeled synthetic transmembrane peptides of bacteriorhodopsin (bR) and enzymatically cleaved C-2 fragment in the solid and dimyristoylphosphatidylcholine bilayer. It turned out that these transmembrane peptides either in hexafluoroisopropanol or cast from it take an ordinary alpha-helix (alpha(I)-helix) irrespective of their amino acid sequences with reference to the conformation-dependent (13)C chemical shifts of (Ala)(n) taking the alpha-helix form. These transmembrane peptides are not always static in the lipid bilayer as in the solid state but undergo rigid-body motions with various frequencies as estimated from suppressed peaks either by fast isotropic or large-amplitude motions (>10(8) Hz) or intermediate frequencies (10(5) or 10(3) Hz). Further, (13)C chemical shifts of the [3-(13)C]Ala-labeled peptides in the bilayer were displaced downfield by 0.3-1.1 ppm depending upon amino acid sequence with respect to those in the solid state, which were explained in terms of local conformational fluctuation (10(2) Hz) deviated from the torsion angles (alpha(II)-helix) from those of standard alpha-helix, under anisotropic environment in lipid bilayer, in addition to the above-mentioned rigid-body motions. The carbonyl (13)C peaks, on the other hand, are not sensitively displaced by such local anisotropic fluctuations, because they are more sensitive to the manner of hydrogen-bond interactions. The amino acid sequences of these peptides inserted within the bilayer were not always the same as those of intact bR, causing disposition of the transmembrane alpha-helical segment from that of intact bR. Finally, we confirmed that the (13)C NMR peak positions of the random coil form are located at the boundary between the alpha-helix and a turned structure in loop regions.

Alteration of conformation and dynamics of bacteriorhodopsin induced by protonation of Asp 85 and deprotonation of Schiff base as studied by 13C NMR

According to previous X-ray diffraction studies, the D85N mutant of bacteriorhodopsin (bR) with unprotonated Schiff base assumes a protein conformation similar to that in the M photointermediate. We recorded (13)C NMR spectra of [3-(13)C]Ala- and [1-(13)C]Val-labeled D85N and D85N/D96N mutants at ambient temperature to examine how conformation and dynamics of the protein backbone are altered when the Schiff base is protonated (at pH 7) and unprotonated (at pH 10). Most notably, we found that the peak intensities of three to four [3-(13)C]Ala-labeled residues from the transmembrane alpha-helices, including Ala 39, 51, and 53 (helix B) and 215 (helix G), were suppressed in D85N and D85N/D96N both from CP-MAS (cross polarization-magic angle spinning) and DD-MAS (dipolar decoupled-magic angle spinning) spectra, irrespective of the pH. This is due to conformational change and subsequent acquisition of intermediate time-range motions, with correlation times in the order of 10(-)(5) or 10(-)(4) s, which interferes with proton decoupling frequency or frequency of magic angle spinning, respectively, essential for an attempted peak-narrowing to achieve high-resolution NMR signals. Greater changes were achieved, however, at pH 10, which indicate large-amplitude motions of transmembrane helices upon deprotonation of Schiff base and the formation of the M-like state in the absence of illumination. The spectra detected more rapid motions in the extracellular and/or cytoplasmic loops, with correlation times increasing from 10(-)(4) to 10(-)(5) s. Conformational changes in the transmembrane helices were located at helices B, G, and D as viewed from the above-mentioned spectral changes, as well as at 1-(13)C-labeled Val 49 (helix B), 69 (B-C loop), and [3-(13)C]Ala-labeled Ala 126 (D-helix) signals, in addition to the cytoplasmic and extracellular loops. Further, we found that in the M-like state the charged state of Asp 96 at the cytoplasmic side substantially modulated the conformation and dynamics of the extracellular region through long-distance interaction.

Conformation and backbone dynamics of bacteriorhodopsin revealed by (13)C-NMR

It is demonstrated here how the secondary structure and dynamics of transmembrane helices, as well as surface residues, such as interhelical loops and N- or C-terminus of bacteriorhodopsin (bR) in purple membrane, can be determined at ambient temperature based on very simple (13)C-NMR measurements, together with a brief experimental background. In contrast to the static picture of bR, currently available from X-ray diffraction or cryo-electron microscopy, the structure consists of dynamically heterogeneous domains which undergo various types of local fluctuations with a frequency range of 10(2)--10 (8) Hz. The significance of this picture is discussed in relation to the biological function of this protein.

Conformational transitions and fibrillation mechanism of human calcitonin as studied by high-resolution solid-state 13C NMR

Conformational transitions of human calcitonin (hCT) during fibril formation in the acidic and neutral conditions were investigated by high-resolution solid-state 13C NMR spectroscopy. In aqueous acetic acid solution (pH 3.3), a local alpha-helical form is present around Gly10 whereas a random coil form is dominant as viewed from Phe22, Ala26, and Ala31 in the monomer form on the basis of the 13C chemical shifts. On the other hand, a local beta-sheet form as viewed from Gly10 and Phe22, and both beta-sheet and random coil as viewed from Ala26 and Ala31 were detected in the fibril at pH 3.3. The results indicate that conformational transitions from alpha-helix to beta-sheet, and from random coil to beta-sheet forms occurred in the central and C-terminus regions, respectively, during the fibril formation. The increased 13C resonance intensities of fibrils after a certain delay time suggests that the fibrillation can be explained by a two-step reaction mechanism in which the first step is a homogeneous association to form a nucleus, and the second step is an autocatalytic heterogeneous fibrillation. In contrast to the fibril at pH 3.3, the fibril at pH 7.5 formed a local beta-sheet conformation at the central region and exhibited a random coil at the C-terminus region. Not only a hydrophobic interaction among the amphiphilic alpha-helices, but also an electrostatic interaction between charged side chains can play an important role for the fibril formation at pH 7.5 and 3.3 acting as electrostatically favorable and unfavorable interactions, respectively. These results suggest that hCT fibrils are formed by stacking antiparallel beta-sheets at pH 7.5 and a mixture of antiparallel and parallel beta-sheets at pH 3.3.

Conformation and dynamics of melittin bound to magnetically oriented lipid bilayers by solid-state (31)P and (13)C NMR spectroscopy

The conformation and dynamics of melittin bound to the dimyristoylphosphatidylcholine (DMPC) bilayer and the magnetic orientation in the lipid bilayer systems were investigated by solid-state (31)P and (13)C NMR spectroscopy. Using (31)P NMR, it was found that melittin-lipid bilayers form magnetically oriented elongated vesicles with the long axis parallel to the magnetic field above the liquid crystalline-gel phase transition temperature (T(m) = 24 degrees C). The conformation, orientation, and dynamics of melittin bound to the membrane were further determined by using this magnetically oriented lipid bilayer system. For this purpose, the (13)C NMR spectra of site-specifically (13)C-labeled melittin bound to the membrane in the static, fast magic angle spinning (MAS) and slow MAS conditions were measured. Subsequently, we analyzed the (13)C chemical shift tensors of carbonyl carbons in the peptide backbone under the conditions where they form an alpha-helix and reorient rapidly about the average helical axis. Finally, it was found that melittin adopts a transmembrane alpha-helix whose average axis is parallel to the bilayer normal. The kink angle between the N- and C-terminal helical rods of melittin in the lipid bilayer is approximately 140 degrees or approximately 160 degrees, which is larger than the value of 120 degrees determined by x-ray diffraction studies. Pore formation was clearly observed below the T(m) in the initial stage of lysis by microscope. This is considered to be caused by the association of melittin molecules in the lipid bilayer.

Irreversible conformational change of bacterio-opsin induced by binding of retinal during its reconstitution to bacteriorhodopsin, as studied by (13)C NMR

We compared (13)C NMR spectra of [3-(13)C]Ala- and [1-(13)C]Val-labeled bacterio-opsin (bO), produced either by bleaching bR with hydroxylamine or from a retinal-deficient strain, with those of bacteriorhodopsin (bR), in order to gain insight into the conformational changes of the protein backbone that lead to correct folding after retinal is added to bO. The observed (13)C NMR spectrum of bO produced by bleaching is not greatly different from that of bR, except for the presence of suppressed or decreased peak-intensities. From careful evaluation of the intensity differences between cross polarization magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) spectra, it appears that the reduced peak-intensities arise from reduced efficiency of cross polarization or interference of internal motions with proton decoupling frequencies. In particular, the E-F and F-G loops and some transmembrane helices of the bleached bO have acquired internal motions whose frequencies interfere with proton decoupling frequencies. In contrast, the protein backbone of the bO from the retinal-negative cells is incompletely folded. Although it contains mainly a-helices, its very broad (13)C NMR signals indicate that its tertiary structure is different from bR. Importantly, this changed structure is identical in form to that of bleached bO from wild-type bR after it was regenerated with retinal in vitro, and bleached with hydroxylamine. We conclude that the binding of retinal is essential for the correct folding of bR after it is inserted in vitro into the lipid bilayer, and the final folded state does not revert to the partially folded form upon removal of the retinal.

Conformational changes of bacteriorhodopsin along the proton-conduction chain as studied with (13)C NMR of [3-(13)C]Ala-labeled protein: arg(82) may function as an information mediator

We have recorded (13)C NMR spectra of [3-(13)C]Ala-labeled wild-type bacteriorhodopsin (bR) and its mutants at Arg(82), Asp(85), Glu(194), and Glu(204) along the extracellular proton transfer chain. The upfield and downfield displacements of the single carbon signals of Ala(196) (in the F-G loop) and Ala(126) (at the extracellular end of helix D), respectively, revealed conformational differences in E194D, E194Q, and E204Q from the wild type. The same kind of conformational change at Ala(126) was noted also in the Y83F mutant, which lacks the van der Waals contact between Tyr(83) and Ala(126) present in the wild type. The absence of a negative charge at Asp(85) in the site-directed mutant D85N induced global conformational changes, as manifested in displacements or suppression of peaks from the transmembrane helices, cytoplasmic loops, etc., as well as the local changes at Ala(126) and Ala(196) seen in the other mutants. Unexpectedly, no conformational change at Ala(126) was observed in R82Q (even though Asp(85) is protonated at pH 6) or in D85N/R82Q. The changes induced in the Ala(126) signal when Asp(85) is uncharged could be interpreted therefore in terms of displacement of the positive charge of Arg(82) toward Tyr(83), where Ala(126) is located. It is possible that disruption of the proton transfer chain after protonation of Asp(85) in the photocycle could cause the same kind of conformational change we detect at Ala(196) and Ala(126). If so, the latter change would be also the result of rearrangement of the side chain of Arg(82).

Long-distance effects of site-directed mutations on backbone conformation in bacteriorhodopsin from solid state NMR of [1-13C]Val-labeled proteins

We have recorded 13C cross-polarization-magic angle spinning and dipolar decoupled-magic angle spinning NMR spectra of [1-13C]Val-labeled wild-type bacteriorhodopsin (bR), and the V49A, V199A, T46V, T46V/V49A, D96N, and D85N mutants, in order to study conformational changes of the backbone caused by site-directed mutations along the extracellular surface and the cytoplasmic half channel. On the basis of spectral changes in the V49A and V199A mutants, and upon specific cleavage by chymotrypsin, we assigned the three well-resolved 13C signals observed at 172.93, 172.00, and 171. 11 ppm to [1-13C]Val 69, Val 49, and Val 199, respectively. The local conformations of the backbone at these residues are revealed by the conformation-dependent 13C chemical shifts. We find that at the ambient temperature of these measurements Val 69 is not in a beta-sheet, in spite of previous observations by electron microscopy and x-ray diffraction at cryogenic temperatures, but in a flexible turn structure that undergoes conformational fluctuation. Results with the T46V mutant suggest that there is a long-distance effect on backbone conformation between Thr 46 and Val 49. From the spectra of the D85N and E204Q mutants there also appears to be coupling between Val 49 and Asp 85 and between Asp 85 and Glu 204, respectively. In addition, the T2 measurement indicates conformational interaction between Asp 96 and extracellular surface. The protonation of Asp 85 in the photocycle therefore might induce changes in conformation or dynamics, or both, throughout the protein, from the extracellular surface to the side chain of Asp 96.

Location of a cation-binding site in the loop between helices F and G of bacteriorhodopsin as studied by 13C NMR

The high-affinity cation-binding sites of bacteriorhodopsin (bR) were examined by solid-state 13C NMR of samples labeled with [3-13C]Ala and [1-13C]Val. We found that the 13C NMR spectra of two kinds of blue membranes, deionized (pH 4) and acid blue at pH 1.2, were very similar and different from that of the native purple membrane. This suggested that when the surface pH is lowered, either by removal of cations or by lowering the bulk pH, substantial change is induced in the secondary structure of the protein. Partial replacement of the bound cations with Na+, Ca2+, or Mn2+ produced additional spectral changes in the 13C NMR spectra. The following conclusions were made. First, there are high-affinity cation-binding sites in both the extracellular and the cytoplasmic regions, presumably near the surface, and one of the preferred cation-binding sites is located at the loop between the helix F and G (F-G loop) near Ala196, consistent with the 3D structure of bR from x-ray diffraction and cryoelectron microscopy. Second, the bound cations undergo rather rapid exchange (with a lifetime shorter than 3 ms) among various types of cation-binding sites. As expected from the location of one of the binding sites, cation binding induced conformational alteration of the F-G interhelical loop.

Evidence of local conformational fluctuations and changes in bacteriorhodopsin, dependent on lipids, detergents and trimeric structure, as studied by 13C NMR

We examined how the local conformation and dynamics of [3-13C]Ala-labeled bacteriorhodopsin (bR) are altered as viewed from 13C NMR spectra when the natural membrane lipids are partly or completely replaced with detergents. It turned out that the major conformational features of bR, the alphaII-helices, are generally unchanged in the delipidated or solubilized preparations. Upon partial delipidation or detergent solubilization, however, a significant conformational change occurs, ascribed to local conversion of alphaII-->alphaI-helix (one Ala residue involved), evident from the upfield displacement of the transmembrane helical peak from 16.4 ppm to 14.5 ppm, conformational change (one or two Ala residues) within alphaII-helices from 16.4 to 16.0 ppm, and acquired flexibility in the loop region (especially at the F-G loop) as manifested from suppressed peak-intensities in cross-polarization magic angle spinning (CP-MAS) NMR spectra. On the other hand, formation of monomers as solubilized by Triton X-100, Triton N-101 and n-dodecylmaltoside is characterized by the presence of a peak at 15.5 ppm and a shifted absorption maximum (550 nm). The size of micelles under the first two conditions was small enough to yield 13C NMR signals observable by a solution NMR spectrometer, although 13C CP-MAS NMR signals were also visible from a fraction of large-sized micelles. We found that the 16.9 ppm peak (three Ala residues involved), visible by CP-MAS NMR, was displaced upfield when Schiff base was removed by solubilization with sodium dodecyl sulfate, consistent with our previous finding of bleaching to yield bacterioopsin.

Existence of a proton transfer chain in bacteriorhodopsin: participation of Glu-194 in the release of protons to the extracellular surface

Glu-194 near the extracellular surface of bacteriorhodopsin is indispensable for proton release to the medium upon protonation of Asp-85 during light-driven transport. As for Glu-204, its replacement with glutamine (but not aspartate) abolishes both proton release and the anomalous titration of Asp-85 that originates from coupling between the pKa of this buried aspartate and those of the other acidic groups. Unlike the case of Glu-204, however, replacement of Glu-194 with aspartate raises the pKa for proton release. In Fourier transform infrared spectra of the E194D mutant a prominent positive band is observed at 1720 cm-1. It can be assigned from [4-13C]aspartate and D2O isotope shifts to the C&dbd;O stretch of protonated Asp-194. Its rise correlates with proton transfer from the retinal Schiff base to Asp-85. Its decay coincides with the appearance of a proton at the surface, detected under similar conditions with fluorescein covalently bound to Lys-129 and with pyranine. Its amplitude decreases with increasing pH, with a pKa of about 9. We show that this pKa is likely to be that of the internal proton donor to Asp-194, the Glu-204 site, before photoexcitation, while 13C NMR titration indicates that Asp-194 has an initial pKa of about 3. We propose that there is a chain of interacting residues between the retinal Schiff base and the extracellular surface. After photoisomerization of the retinal the pKa's change so as to allow (i) Asp-85 to become protonated by the Schiff base, (ii) the Glu-204 site to transfer its proton to Asp-194 in E194D, and therefore to Glu-194 in the wild type, and (iii) residue 194 to release the proton to the medium.

Stability of the C-terminal alpha-helical domain of bacteriorhodopsin that protrudes from the membrane surface, as studied by high-resolution solid-state 13C NMR

We have recorded 13C NMR spectra of [1-(13)C]Ala- and [3-(13)C]Ala-bacteriorhodopsin (bR), [1-(13)C]Ala- and [3-(13)C]Ala-papain-cleaved bR, and [3-(13)C]Ala-labeled R227Q bR mutant by cross polarization-magic angle spinning (CP-MAS) and dipolar decoupled-magic angle spinning (DD-MAS) methods. The pH and temperature were varied, and Arg 227 was replaced with Gln (R227Q), in order to clarify their effects on the stability of the alpha-helical domain of the C-terminus that protrudes from the membrane surface. The comparative 13C CP- and DD-MAS NMR study of [3-(13)C]Ala-bR, rather than [1-(13)C]Ala-bR, turned out to be the best means to distinguish the 13C NMR signals of the C-terminus from those of the rest of the transmembrane helices or loops. The inner segment of the C-terminus, from Ala 228 to Ala 235, forms an alpha-helical domain (resonated at 15.9 ppm) either at neutral pH and/or at 10 to -10 degrees C. The alpha-helical peak was not seen, however, after either cleavage of the C-terminus with papain or lowering the pH to 4.25. This alpha-helical structure, and a part of the random coil which was produced from the helix at pH 4.25, were further converted to a low-temperature-type alpha-helix, as indicated by an upfield displacement of the 13C NMR signal, when the temperature was lowered to 10- -10 degrees C. Surprisingly, the corresponding helical structure in R227Q is more stable than in the wild type at the acidic pH. This alpha-helical peak was classified as an alphaII-helix from the 13C chemical shifts of Cbeta carbon, although it was ascribed to an alphaI-helix on the basis of the carbonyl shifts. This is in contrast to Ala 53 which adopts the alphaII-helix as judged from the 13C chemical shifts of Cbeta and the carbonyl carbons. Therefore, this discrepancy might be caused by differential sensitivity of the two types of carbon signals to conformation and to modes of hydrogen bonding when motional fluctuation is involved. It is likely that the alphaII-helix form present at the C-terminus is not always the type originally proposed but should be considered as a form undergoing large-amplitude conformational fluctuation around alpha-helix.

[Successful induction of immune tolerance and novel hemostatic effects in a hemophilia A with high-responder inhibitor by regular infusions of factor VIII]

A hemophilia A patient with high responder inhibitor had been treated by (activated) prothrombin complex concentrates (A) PCC and activated factor VII until the occurrence of intracranial bleeding at the age of 6 years. Since the inhibitor titer was decreased less than 1 Bethesda Units/ml, high dose of factor VIII was given followed by the infusions of factor VIII concentrates (100 units/kg) three times a week. In spite of previous episodes of anamnestic responses by factor VIII products before, the inhibitor titer did not increase and disappeared completely 6 months after the FVIII infusion therapy. The specific anti-factor VIII IgG subclasses of the inhibitor were IgG2 and IgG4. The inhibitor recognized both light and heavy chains. He have no bleeding episode for 6 months since the beginning of the prophylactic with factor VIII concentrates.

Temperature-dependent conformational change of bacteriorhodopsin as studied by solid-state 13C NMR

Cross-polarization and dipolar-decoupled magic-angle spinning 13C-NMR spectra of [3-13C]Ala-labelled bacteriorhodopsin were obtained for hydrated purple membrane in the temperatures range 23 degrees C to -110 degrees C. Well-resolved 13C-NMR signals were observed either at ambient temperature or at -20 degrees C but were broadened considerably at lower temperature below -40 degrees C. This situation was interpreted in terms of the presence of exchange processes with a rate constant of 10(2) s-1 at ambient temperature among several conformations slightly different from each other. We found that such an exchange process was strongly influenced by the manner of organization of the lipid bilayers depending upon the presence or absence of cations responsible for electric shielding of negative charge at the polar head groups. The manner of organization of the lipid bilayers was conveniently characterized by a characteristic temperature at which the methyl peaks of fatty acyl groups of lipids in the purple membrane were suppressed due to interference of motional frequency with the decoupling frequency (10-100 kHz) for preparations containing 10 mM NaCl or CaCl2. No such spectral change in the absence of these cations was noted even if a preparation was cooled to -110 degrees C. The secondary structures of [3-13C]Ala-labelled bacteriorhodopsin was not always identical at temperatures between ambient and low temperatures, since the 13C chemical shifts and relative peak intensities for purple membrane preparations containing these salts changed with temperature in the range -110 degrees C to 23 degrees C. In particular, we found that some residues involving Ala residues at the alpha II-helix and loop region were converted at temperatures below -60 degrees C to a conformation involving alpha 1-helix. In other words, some portion of the alpha-helical conformation of bacteriorhodopsin proposed from results obtained by cryo-electron microscopy, at very low temperatures, is not always retained at ambient temperature.

Conformation and dynamics of [3-13C]Ala- labeled bacteriorhodopsin and bacterioopsin, induced by interaction with retinal and its analogs, as studied by 13C nuclear magnetic resonance

13C nuclear magnetic resonance (NMR) spectra of [3-13C]Ala-labeled bacteriorhodopsin (bR), bacterioopsin (bO), and regenerated bR with retinal or bO complex with retinal analogs were recorded in order to gain insights into how the conformation and dynamics of apoprotein (bO) vary with or without retinal or its analogs. First, we assigned the 13C NMR peak resonating at 16.3 ppm to Ala 53 of both bR and bO, which appears to contact the side chain of Lys 216 at the site of the Schiff base in the former, utilizing the 13C NMR peaks of A53V and A53G proteins in comparison with those of wild-type bR and bO. Characteristic spectral differences between the apoprotein and bR were observed upon removal of the retinal: the changes of the peak intensities at 16.4, 15.9, and 16.9 ppm are notable. We found that the loops (17.4 ppm) and transmembrane alpha II helical region (15.9 ppm) acquired motional freedom with a correlation time of 10(-5)s when the retinal was removed, as detected by proton spin-lattice relaxation times in the rotating frame. A 13C NMR spectrum very similar to that of native bR was recorded when bR was regenerated by addition of retinal to bO. On the other hand, the addition of the retinal analogs retinol or beta-ionone, which are bound in the retinal binding site but are incapable of forming a Schiff base to the apoprotein, caused distinct spectral changes different from those of bR, as manifested from the displacements of 13C chemical shifts. These spectral changes must be ascribed to significant conformational changes of apoprotein at various locations in the protein, including the site of Ala 53 induced by modified interaction between the apoprotein and chromophore.

Hydrogen bonds of water and C==O groups coordinate long-range structural changes in the L photointermediate of bacteriorhodopsin

Fourier transform infrared spectra of light-adapted bacteriorhodopsin exhibit a band at 1618 cm(-1) that shifts to 1625 cm(-1) upon formation of the L intermediate. It is assigned to the peptide C==O of Val49 from the fact that it shifts in [1-(13)C]valine-labeled bacteriorhodopsin and appears perturbed in the Val49-->Met mutant. The intensity of the BR-->L difference band is reduced in the Thr46-->Val mutant but restored by the additional mutation of Asp96-->Asn. These intensity changes are closely correlated with the H-bonding change of water olecules, suggesting that the peptide C==O of Val49 is hydrated. This could arise in the Thr46-->Val mutant because of perturbation of the C==O of Val46, which points toward Val49. The Val49-->Ala mutation influences a peptide N-H, presumably of Val49, and the carboxylic C==O of Asp96, as well as water molecules proximal to Asp85. Conversely, the water molecule assumed to be in the cavity that arises from the missing two methyl groups in V49A could be affected in the mutant of Asp96-->Asn. We propose that the perturbation exerted on Asp85 by the Schiff base in the L intermediate is transmitted to Asp96 through H-bonding of water molecules in the Asp85-Val49 region, the C==O of Val49, H-bonding between Val49 and Thr46, and H-bonding between Thr46 and Asp96.

13C NMR study on conformation and dynamics of the transmembrane alpha-helices, loops, and C-terminus of [3-13C]Ala-labeled bacteriorhodopsin

We have recorded 13C CP-MAS and DD-MAS NMR spectra of untreated and deionized [3-13C]-Ala-labeled bacteriorhodopsin (bR) and those cleaved with carboxypeptidase A and papain to gain insight into the conformation and dynamics of the transmembrane alpha-helices, loops, and C-terminus. It turned out that the C-terminus does not contribute to the 13C CP-MAS NMR spectra of [3-13C]Ala-bR recorded at ambient temperature owing to its rapid reorientational motions, since the relative peak intensities were unchanged in spite of the enzymatic cleavages. Therefore, the 13C CP-MAS NMR peaks of bR should be ascribed both to the transmembrane alpha-helices and loops. We further distinguished the peaks of the alpha II-helix form at 16.3 ppm (60%) from those of the alpha I-helix form at 14.9 ppm (20%) by deconvolution of the respective peaks of the hydrated [3-13C]Ala-bR, as referred to the 13C chemical shift of polyalanine in hexafluoroisopropyl alcohol. The remaining CP-MAS NMR peak of [3-13C]Ala-bR at 17.2 ppm was ascribed to the loops (20%) taking a variety of turn structures. In contrast, the 13C NMR signals from the C-terminal residues were significantly enhanced by recording the dipolar-decoupled (DD)-MAS NMR spectra. Conformational features of the two different portions of the C-terminus, residues 245-248 and 231-244, were revealed by the conformation-dependent 13C signals of bR successively cleaved by carboxypeptidase A and papain, respectively. The terminal end, residues 245-248, containing two Ala residues is virtually disordered and undergoing rapid motions.(ABSTRACT TRUNCATED AT 250 WORDS)

A high-resolution 15N solid-state NMR study of collagen and related polypeptides. The effect of hydration on formation of interchain hydrogen bonds as the primary source of stability of the collagen-type triple helix

High-resolution solid-state 15N-NMR was used to clarify the effect of hydration on the stability of the coiled-coil triple-helix conformation of Gly-Xaa-Yaa repeating units in collagen and the collagen-like polypeptides, (Pro-Ala-Gly)n and (Pro-Pro-Gly)10, because the stability is thought to be related to the presence of (Gly)NH ... O = C(Xaa or Pro) hydrogen bonds. The 15N-NMR signals of these samples were narrowed upon hydration, mainly due to hydration-induced conformational change or rearrangement of the repeating units. In particular, the 15N chemical shifts of the Gly N-H group and the high-field (low-frequency) shoulder peak of Pro nitrogen signals in (Pro-Pro-Gly)10 were shifted downfield (4.9 ppm and 6.8 ppm, respectively) with increasing relative humidity, while the corresponding peaks for collagen and (Pro-Ala-Gly)n were unchanged and close to the 15N shift of (Pro-Pro-Gly)10 in the hydrated state. Such downfield shifts are consistent with the formation of N-H ... O = C hydrogen bonds. In agreement with the NMR results, it was found that the (Gly)NH ... O = C (Xaa or Pro) hydrogen bonds are retained in dehydrated collagen fibrils but not in partially dehydrated (Pro-Pro-Gly)10. No evidence was obtained for the partial formation of the 3(1) helix form (Pro)n or (Gly)n either under hydrated or dehydrated conditions. It is concluded that the Gly 15N chemical shift is a very sensitive probe for studying supercoiling in collagen and collagen-like polypeptides.

A high-resolution solid-state 13C-NMR study on [1-13C]Ala and [3-13C]Ala and [1-13C]Leu and Val-labelled bacteriorhodopsin. Conformation and dynamics of transmembrane helices, loops and termini, and hydration-induced conformational change

We have recorded 100.7-MHz high-resolution solid-state 13C-NMR spectra of [3-13C]Ala, [1-13C]Ala-labelled, Leu-labelled and Val-labelled bacteriorhodopsin (bR), to analyze the conformation and dynamics of transmembrane alpha helices and hydration-induced conformational changes. We assigned the 13C-NMR signals of these 13C-labelled amino acid residues to portions of the transmembrane alpha helices, loops and N-terminus and C-terminus, based on the conformation-dependent 13C chemical shift. The assignment of peaks to the transmembrane alpha helices is straightforward in view of the characteristic 13C chemical shifts of the C beta and carbonyl carbons, referred to the data of the model system. The signals of the transmembrane alpha helices were further divided into three or four peaks which are ascribed to either a dispersion of torsion angles of the alpha helices or variation of environments around the helices. In addition, we found that conformation of the N-terminus and C-terminus of bR is virtually the random-coil form which undergoes rapid reorientational motion in the hydrated system. Further, we show that the higher-order (secondary and/or tertiary) structure of bR is influenced by the hydration/dehydration process of the purple membrane, as viewed from the peak profile of the Ala C beta 13C signals. This change of structure occurs between relative humidities of 2% and 4%, consistent with the shift of the absorption maxima of retinal, which arise from the protonation/deprotonation processes of the Schiff base. In contrast, no such change of the carbonyl signals occurs for the Leu, Val and Ala residues. For the latter two residues, some spectral changes were noted at the stage of full hydration.

A high-resolution solid-state 13C-NMR study on crystalline bovine heart cytochrome-c oxidase and lysozyme. Dynamic behavior of protein and detergent in the complex

We have recorded 100.6-MHz high-resolution solid-state 13C-NMR spectra of crystalline cytochrome-c oxidase from bovine heart muscle and hen egg-white lysozyme, to compare conformation and dynamics of a typical membrane-protein complex with those of lysozyme. The absence of severe interference with the solid-state 13C-NMR spectra, from both the line broadenings from paramagnetic centers and overlapping of intense detergent signals, provided spectral resolution of 13C-NMR feature of cytochrome-c oxidase crystals comparable to that of lysozyme crystal and better than that of dissolved or lyophilized samples. In fact, the observed peak intensities of the polar heads of the detergents BL8SY and Brij 35 were only about 10% and 3% of the anticipated values, respectively. The dynamic behavior of the backbone and side chains of cytochrome-c oxidase was compared with that of lysozyme on the basis of the 13C spin-lattice relaxation times (T1): the backbone of the cytochrome-c oxidase turned out to be more flexible than that of lysozyme. Molecular motions of the detergent molecules attached to the proteins are found to be highly heterogeneous. Detergent molecules undergo rapid tumbling motions in the crystals in about 10 ns as detected by T1. In addition to rapid motions, slow motions were detected by 1H spin-lattice relaxation time in the rotating frame (TH1 rho) and cross-polarization time (TCH), together with data from static spectra, indicating that the aliphatic portion of the detergent interacts more strongly with hydrophobic protein surfaces than do the polar heads.