Abstract:

A distinguishing feature of rod arrestin is its ability to form oligomers at physiological concentrations. Using visible light scattering, we show that rod arrestin forms tetramers in a cooperative manner in solution. To investigate the structure of the tetramer, a nitroxide side chain (R1) was introduced at 18 different positions. The effects of R1 on oligomer formation, EPR spectra, and inter-spin distance measurements all show that the structures of the solution and crystal tetramers are different. Inter-subunit distance measurements revealed that only arrestin monomer binds to light-activated phosphorhodopsin, whereas both monomer and tetramer bind microtubules, which may serve as a default arrestin partner in dark-adapted photoreceptors. Thus, the tetramer likely serves as a 'storage' form of arrestin, increasing the arrestin-binding capacity of microtubules while readily dissociating to supply active monomer when it is needed to quench rhodopsin signaling.

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Structure and function of the visual arrestin oligomer

^{Department of Pharmacology, Vanderbilt University, Nashville, TN, USA}

^{Jules Stein Eye Institute and Department of Chemistry and Biochemistry, UCLA, Los Angeles, CA, USA}

^{Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA}

^{Albert Eye Research Institute, Duke University Medical Center, Durham, NC, USA}

^{Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA. Tel.: +1 615 322 7070; Fax: +1 615 343 6532; E-mail:}ude.tlibrednav@hciverug.dolovesv

^{Jules Stein Eye Institute and Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles, CA 90095, USA; Tel.: +1 310 206 8830; Fax: +1 310 794 2144; E-mail:}ude.alcu.iesj@wllebbuh

^{Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Tel.: +1 414 456 4015; Fax: +1 414 456 6512; E-mail:}ude.wcm@ecidnac

^{These authors contributed equally to this work}

Received 2006 Sep 22; Accepted 2007 Jan 26.

Abstract

A distinguishing feature of rod arrestin is its ability to form oligomers at physiological concentrations. Using visible light scattering, we show that rod arrestin forms tetramers in a cooperative manner in solution. To investigate the structure of the tetramer, a nitroxide side chain (R1) was introduced at 18 different positions. The effects of R1 on oligomer formation, EPR spectra, and inter-spin distance measurements all show that the structures of the solution and crystal tetramers are different. Inter-subunit distance measurements revealed that only arrestin monomer binds to light-activated phosphorhodopsin, whereas both monomer and tetramer bind microtubules, which may serve as a default arrestin partner in dark-adapted photoreceptors. Thus, the tetramer likely serves as a ‘storage' form of arrestin, increasing the arrestin-binding capacity of microtubules while readily dissociating to supply active monomer when it is needed to quench rhodopsin signaling.

Keywords: arrestin, EPR, oligomer, photoreceptor, signaling

Abstract

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Acknowledgments

We are grateful to Drs MJ Kennedy and JB Hurley for mass spectrometric characterization of phosphorhodopsin and Mrs Cherie Hubbell and Mr Nicholas J Bessman for technical assistance. This work was supported by NIH grants EY11500 (VVG), EY05216 and the Jules Stein Professorship Endowment (WLH), AI58024 and GM70642 (CSK), and EY10336 (VYA). SMH was supported by Training Grant GM07628.

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