The angles between the C1-, C5-, and C9-methyl bonds of the retinylidene chromophore and the membrane normal increase in the M intermediate of bacteriorhodopsin: Direct determination with solid-state 2H NMR

Stephan Moltke, Ingrid Wallat, Naomi Sakai, Koji Nakanishi, Michael F Brown, Maarten P. Heyn

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Abstract

The orientations of three methyl bonds of the retinylidene chromophore of bacteriorhodopsin were investigated in the M photointermediate using deuterium solid-state NMR (2H NMR). In this key intermediate, the chromophore has a 13-cis, 15-anti conformation and a deprotonated Schiff base. Purple membranes containing wild-type or mutant D96A bacteriorhodopsin were regenerated with retinals specifically deuterated in the methyl groups of either carbon C1 or C5 of the β-ionone ring or carbon C9 of the polyene chain. Oriented hydrated films were formed by drying concentrated suspensions on glass plates at 86% relative humidity. The lifetime of the M state was increased in the wild-type samples by applying a guanidine hydrochloride solution at pH 9.5 and in the D96A sample by raising the pH. 2H NMR experiments were performed on the dark-adapted ground state (a 2:1 mixture of 13-cis, 15-syn and all-trans, 15-anti chromophores), the cryotrapped light-adapted state (all-trans, 15-anti), and the cryotrapped M intermediate (13-cis, 15-anti) at -50 °C. Bacteriorhodopsin was first completely converted to M under steady illumination of the hydrated films at +5 °C and then rapidly cooled to -50 °C in the dark. From a tilt series of the oriented sample in the magnetic field and an analysis of the 2H NMR line shapes, the angles between the individual C-CD3 bonds and the membrane normal could be determined even in the presence of a substantial degree of orientational disorder. While only minor differences were detected between dark- and light-adapted states, all three angles increase in the M state. This is consistent with an upward movement of the C5-C13 part of the polyene chain toward the cytoplasmic surface or with increased torsional strain. The C9-CD3 bond shows the largest orientational change of 7°in M. This reorientation of the chromophore in the binding pocket provides direct structural support for previous suggestions (based on spectroscopic evidence) for a steric interaction in M between the C9-methyl group and Trp 182 in helix F.

Original languageEnglish (US)
Pages (from-to)11762-11772
Number of pages11
JournalBiochemistry
Volume38
Issue number36
DOIs
StatePublished - Sep 7 1999

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Bacteriorhodopsins
Polyenes
Chromophores
Nuclear magnetic resonance
Membranes
Carbon
Purple Membrane
Norisoprenoids
Light
Schiff Bases
Deuterium
Guanidine
Magnetic Fields
Humidity
Lighting
Glass
Suspensions
Ground state
Conformations
Atmospheric humidity

ASJC Scopus subject areas

  • Biochemistry

Cite this

The angles between the C1-, C5-, and C9-methyl bonds of the retinylidene chromophore and the membrane normal increase in the M intermediate of bacteriorhodopsin : Direct determination with solid-state 2H NMR. / Moltke, Stephan; Wallat, Ingrid; Sakai, Naomi; Nakanishi, Koji; Brown, Michael F; Heyn, Maarten P.

In: Biochemistry, Vol. 38, No. 36, 07.09.1999, p. 11762-11772.

Research output: Contribution to journalArticle

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abstract = "The orientations of three methyl bonds of the retinylidene chromophore of bacteriorhodopsin were investigated in the M photointermediate using deuterium solid-state NMR (2H NMR). In this key intermediate, the chromophore has a 13-cis, 15-anti conformation and a deprotonated Schiff base. Purple membranes containing wild-type or mutant D96A bacteriorhodopsin were regenerated with retinals specifically deuterated in the methyl groups of either carbon C1 or C5 of the β-ionone ring or carbon C9 of the polyene chain. Oriented hydrated films were formed by drying concentrated suspensions on glass plates at 86{\%} relative humidity. The lifetime of the M state was increased in the wild-type samples by applying a guanidine hydrochloride solution at pH 9.5 and in the D96A sample by raising the pH. 2H NMR experiments were performed on the dark-adapted ground state (a 2:1 mixture of 13-cis, 15-syn and all-trans, 15-anti chromophores), the cryotrapped light-adapted state (all-trans, 15-anti), and the cryotrapped M intermediate (13-cis, 15-anti) at -50 °C. Bacteriorhodopsin was first completely converted to M under steady illumination of the hydrated films at +5 °C and then rapidly cooled to -50 °C in the dark. From a tilt series of the oriented sample in the magnetic field and an analysis of the 2H NMR line shapes, the angles between the individual C-CD3 bonds and the membrane normal could be determined even in the presence of a substantial degree of orientational disorder. While only minor differences were detected between dark- and light-adapted states, all three angles increase in the M state. This is consistent with an upward movement of the C5-C13 part of the polyene chain toward the cytoplasmic surface or with increased torsional strain. The C9-CD3 bond shows the largest orientational change of 7°in M. This reorientation of the chromophore in the binding pocket provides direct structural support for previous suggestions (based on spectroscopic evidence) for a steric interaction in M between the C9-methyl group and Trp 182 in helix F.",
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AU - Wallat, Ingrid

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AU - Heyn, Maarten P.

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N2 - The orientations of three methyl bonds of the retinylidene chromophore of bacteriorhodopsin were investigated in the M photointermediate using deuterium solid-state NMR (2H NMR). In this key intermediate, the chromophore has a 13-cis, 15-anti conformation and a deprotonated Schiff base. Purple membranes containing wild-type or mutant D96A bacteriorhodopsin were regenerated with retinals specifically deuterated in the methyl groups of either carbon C1 or C5 of the β-ionone ring or carbon C9 of the polyene chain. Oriented hydrated films were formed by drying concentrated suspensions on glass plates at 86% relative humidity. The lifetime of the M state was increased in the wild-type samples by applying a guanidine hydrochloride solution at pH 9.5 and in the D96A sample by raising the pH. 2H NMR experiments were performed on the dark-adapted ground state (a 2:1 mixture of 13-cis, 15-syn and all-trans, 15-anti chromophores), the cryotrapped light-adapted state (all-trans, 15-anti), and the cryotrapped M intermediate (13-cis, 15-anti) at -50 °C. Bacteriorhodopsin was first completely converted to M under steady illumination of the hydrated films at +5 °C and then rapidly cooled to -50 °C in the dark. From a tilt series of the oriented sample in the magnetic field and an analysis of the 2H NMR line shapes, the angles between the individual C-CD3 bonds and the membrane normal could be determined even in the presence of a substantial degree of orientational disorder. While only minor differences were detected between dark- and light-adapted states, all three angles increase in the M state. This is consistent with an upward movement of the C5-C13 part of the polyene chain toward the cytoplasmic surface or with increased torsional strain. The C9-CD3 bond shows the largest orientational change of 7°in M. This reorientation of the chromophore in the binding pocket provides direct structural support for previous suggestions (based on spectroscopic evidence) for a steric interaction in M between the C9-methyl group and Trp 182 in helix F.

AB - The orientations of three methyl bonds of the retinylidene chromophore of bacteriorhodopsin were investigated in the M photointermediate using deuterium solid-state NMR (2H NMR). In this key intermediate, the chromophore has a 13-cis, 15-anti conformation and a deprotonated Schiff base. Purple membranes containing wild-type or mutant D96A bacteriorhodopsin were regenerated with retinals specifically deuterated in the methyl groups of either carbon C1 or C5 of the β-ionone ring or carbon C9 of the polyene chain. Oriented hydrated films were formed by drying concentrated suspensions on glass plates at 86% relative humidity. The lifetime of the M state was increased in the wild-type samples by applying a guanidine hydrochloride solution at pH 9.5 and in the D96A sample by raising the pH. 2H NMR experiments were performed on the dark-adapted ground state (a 2:1 mixture of 13-cis, 15-syn and all-trans, 15-anti chromophores), the cryotrapped light-adapted state (all-trans, 15-anti), and the cryotrapped M intermediate (13-cis, 15-anti) at -50 °C. Bacteriorhodopsin was first completely converted to M under steady illumination of the hydrated films at +5 °C and then rapidly cooled to -50 °C in the dark. From a tilt series of the oriented sample in the magnetic field and an analysis of the 2H NMR line shapes, the angles between the individual C-CD3 bonds and the membrane normal could be determined even in the presence of a substantial degree of orientational disorder. While only minor differences were detected between dark- and light-adapted states, all three angles increase in the M state. This is consistent with an upward movement of the C5-C13 part of the polyene chain toward the cytoplasmic surface or with increased torsional strain. The C9-CD3 bond shows the largest orientational change of 7°in M. This reorientation of the chromophore in the binding pocket provides direct structural support for previous suggestions (based on spectroscopic evidence) for a steric interaction in M between the C9-methyl group and Trp 182 in helix F.

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