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Structural characterizationof insoluble proteins often relies on solid‐state NMR spectroscopy. Perdeuteration and partial back‐substitution of exchangeable protons, as proposed for crystalline model proteins, is now shown to lead to beneficial proton spectra for heterogeneous systems, such as fibrils formed by the Alzheimer's disease β‐amyloid peptide Aβ40, the lipid reconstituted β‐barrel membrane protein OmpG, and the α‐helical membrane protein bacteriorhodopsin.

Die strukturelle Charakterisierungvon unlöslichen Proteinen stützt sich auf Festkörper‐NMR‐Spektroskopie. Versuche mit Perdeuterierung und partiellem Rückaustausch, wie sie schon für kristalline Modellproteine vorgeschlagen wurden, erwiesen sich nun auch als vorteilhaft zur Detektion von Protonen in heterogenen Systemen wie Fibrillen, die aus dem Alzheimer'schen β‐Amyloidpeptid Aβ40 gebildet werden, das β‐Fass‐Membranprotein OmpG und das α‐helikale Membranprotein Bakteriorhodopsin.

We used neutron scattering and specific hydrogen-deuterium labeling to investigate the thermal dynamics of isotope-labeled amino acids and retinal, predominantly in the active core and extracellular moiety of bacteriorhodopsin (BR) in the purple membrane and the dynamical response to hydration. Measurements on two neutron spectrometers allowed two populations of motions to be characterized. The lower amplitude motions were found to be the same for both the labeled amino acids and retinal of BR and the global membrane. The larger amplitude dynamics of the labeled part, however, were found to be more resilient than the average membrane, suggesting their functional importance. The response to hydration was characterized, showing that the labeled part of BR is not shielded from hydration effects. The results suggest that the inhibition of high-amplitude motions by lowering hydration may play a key role in the slowing down of the photocycle and the proton pumping activity of BR.

In the purple membrane (PM) of halobacteria, lipids stabilize the trimeric arrangement of bacteriorhodopsin (BR) molecules and mediate the packing of the trimers in a regular crystalline arrangement. To date, the identification and quantification of these lipids has been based either on lipid extraction procedures or structural models. By directly solubilizing PMs from Halobacterium salinarum in aqueous detergent solutions (SDS or Triton X-100), we avoided any separation or modification steps that might modify the lipid composition or even the lipid molecules themselves. Our analysis of integral PM preparations should resolve partially conflicting literature data on the lipid composition of the PM. Using 31P and 1H NMR of detergent-solubilized but otherwise untreated samples, we found two glycolipids and 6.4 ± 0.1 phospholipids per BR molecule, 4.4 ± 0.1 of the latter being the phosphatidylglycerophosphate methyl ester. The only glycolipid detected was S-TGD-1. For an additional glycolipid, glycocardiolipin, that was recently identified in lipid extracts, we show that it was produced mainly during the lipid extraction procedure but also was partially dependent on the preparation of the PM suspensions.

Solid‐state NMR spectroscopyhas recently emerged as a tool for structural biology. Sensitivity and resolution, however, still hamper more widespread applications. Protons are ideal as they have the largest gyromagnetic ratio, but they can induce severe line broadening. As described in the Communication by B. Reif and co‐workers on page 4508 ff.,perdeuteration and partial back‐substitution of exchangeable protons can overcome the strong coupling problem. The approach is successfully implemented for fibrils and membrane proteins.

Die Festkörper‐NMR‐Spektroskopieist ein interessantes Verfahren für die Strukturbiologie, mangelnde Empfindlichkeit und Auflösung stehen aber einer verbreiteten Anwendung im Weg. Protonen sind ideale Detektionsziele, weil sie über das größte gyromagnetische Verhältnis verfügen; allerdings neigen sie auch zu starker Linienverbreiterung. B. Reif und Mitarbeiter beschreiben in ihrer Zuschrift auf S. 4601 ff.,wie das Problem starker Kopplungen durch Perdeuterierung und teilweisen Rücktausch austauschbarer Protonen umgangen werden konnte. Ihr Ansatz war für fibrilläre und Membranproteine erfolgreich.