Weakened coupling of conserved arginine to the proteorhodopsin chromophore and its counterion implies structural differences from bacteriorhodopsin

Ranga Partha; Richard Krebs; Tamara L. Caterino; Mark S. Braiman

doi:10.1016/j.bbabio.2004.12.009

Weakened coupling of conserved arginine to the proteorhodopsin chromophore and its counterion implies structural differences from bacteriorhodopsin

Ranga Partha, Richard Krebs, Tamara L. Caterino, Mark S. Braiman

Department of Chemistry

Research output: Contribution to journal › Article › peer-review

21 Scopus citations

Abstract

In wild-type proteorhodopsin (pR), titration of the chromophore's counterion Asp⁹⁷ occurs with a pK_a of 8.2±0.1. R94C mutation reduces this slightly to 7.0±0.2, irrespective of treatment with ethylguanidinium. This contrasts with the homologous archaeal protein bacteriorhodopsin (bR), where R82C mutation was previously shown to elevate the pK_a of Asp⁸⁵ by ∼5 units, while reconstitution with ethylguanidinium restores it nearly to the wild-type value of 2.5. We conclude there is much weaker electrostatic coupling between Arg⁹⁴ and Asp⁹⁷ in the unphotolyzed state of pR, in comparison to Arg ⁸² and Asp⁸⁵ in bR. Therefore, while fast light-driven H⁺ release may depend on these two residues in pR as in bR, no tightly conserved pre-photolysis configuration of them is required.

Original language	English (US)
Pages (from-to)	6-12
Number of pages	7
Journal	Biochimica et Biophysica Acta - Bioenergetics
Volume	1708
Issue number	1
DOIs	https://doi.org/10.1016/j.bbabio.2004.12.009
State	Published - Jun 1 2005

Keywords

Blue membrane
Fast H release
Light-driven proton pumping
Photocycle
Red to purple transition
Sensory rhodopsin

ASJC Scopus subject areas

Biophysics
Biochemistry
Cell Biology

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10.1016/j.bbabio.2004.12.009

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title = "Weakened coupling of conserved arginine to the proteorhodopsin chromophore and its counterion implies structural differences from bacteriorhodopsin",

abstract = "In wild-type proteorhodopsin (pR), titration of the chromophore's counterion Asp97 occurs with a pKa of 8.2±0.1. R94C mutation reduces this slightly to 7.0±0.2, irrespective of treatment with ethylguanidinium. This contrasts with the homologous archaeal protein bacteriorhodopsin (bR), where R82C mutation was previously shown to elevate the pKa of Asp85 by ∼5 units, while reconstitution with ethylguanidinium restores it nearly to the wild-type value of 2.5. We conclude there is much weaker electrostatic coupling between Arg94 and Asp97 in the unphotolyzed state of pR, in comparison to Arg 82 and Asp85 in bR. Therefore, while fast light-driven H+ release may depend on these two residues in pR as in bR, no tightly conserved pre-photolysis configuration of them is required.",

keywords = "Blue membrane, Fast H release, Light-driven proton pumping, Photocycle, Red to purple transition, Sensory rhodopsin",

author = "Ranga Partha and Richard Krebs and Caterino, {Tamara L.} and Braiman, {Mark S.}",

note = "Funding Information: This work was supported by Syracuse University. Tamara Caterino was supported by an NSF-REU award to the Syracuse University Chemistry Department.",

year = "2005",

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doi = "10.1016/j.bbabio.2004.12.009",

language = "English (US)",

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T1 - Weakened coupling of conserved arginine to the proteorhodopsin chromophore and its counterion implies structural differences from bacteriorhodopsin

AU - Partha, Ranga

AU - Krebs, Richard

AU - Caterino, Tamara L.

AU - Braiman, Mark S.

N1 - Funding Information: This work was supported by Syracuse University. Tamara Caterino was supported by an NSF-REU award to the Syracuse University Chemistry Department.

PY - 2005/6/1

Y1 - 2005/6/1

N2 - In wild-type proteorhodopsin (pR), titration of the chromophore's counterion Asp97 occurs with a pKa of 8.2±0.1. R94C mutation reduces this slightly to 7.0±0.2, irrespective of treatment with ethylguanidinium. This contrasts with the homologous archaeal protein bacteriorhodopsin (bR), where R82C mutation was previously shown to elevate the pKa of Asp85 by ∼5 units, while reconstitution with ethylguanidinium restores it nearly to the wild-type value of 2.5. We conclude there is much weaker electrostatic coupling between Arg94 and Asp97 in the unphotolyzed state of pR, in comparison to Arg 82 and Asp85 in bR. Therefore, while fast light-driven H+ release may depend on these two residues in pR as in bR, no tightly conserved pre-photolysis configuration of them is required.

AB - In wild-type proteorhodopsin (pR), titration of the chromophore's counterion Asp97 occurs with a pKa of 8.2±0.1. R94C mutation reduces this slightly to 7.0±0.2, irrespective of treatment with ethylguanidinium. This contrasts with the homologous archaeal protein bacteriorhodopsin (bR), where R82C mutation was previously shown to elevate the pKa of Asp85 by ∼5 units, while reconstitution with ethylguanidinium restores it nearly to the wild-type value of 2.5. We conclude there is much weaker electrostatic coupling between Arg94 and Asp97 in the unphotolyzed state of pR, in comparison to Arg 82 and Asp85 in bR. Therefore, while fast light-driven H+ release may depend on these two residues in pR as in bR, no tightly conserved pre-photolysis configuration of them is required.

KW - Blue membrane

KW - Fast H release

KW - Light-driven proton pumping

KW - Photocycle

KW - Red to purple transition

KW - Sensory rhodopsin

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Weakened coupling of conserved arginine to the proteorhodopsin chromophore and its counterion implies structural differences from bacteriorhodopsin

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Keywords

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