RESEARCH PROGRAMS AND AFFILIATIONS
Our laboratory is studying light transduction and development in the retina using molecular biological, biochemical and physiological approaches. Light transduction is carried out in specialized cells (rods and cones) that express a group of proteins designed to efficiently capture photons and transmit the information as a change in the conductance of the plasma membrane. The visual pigments (opsins) are a large family of proteins that absorb light and initiate the intracellular signal transduction pathway through a G-protein cascade. Opsins differ from each other in their wavelength of maximum absorbance (permitting color detection), their conformational changes after light activation and in retinal expression patterns. These issues are crucial for shaping a photoreceptor's characteristic response properties. We have a long standing research effort to understand thare studying how photoreceptors develop and the molecular basis of rod/cone opsin functional differences.
The control of retinal gene transcription involves numerous cis-acting DNA elements in the proximal promoter, as well as more distant sequences. A complete understanding of the mechanism of transcriptional control that leads to cell-specific expression will require detailed experiments in vivo. We have developed transient transfections assays of embryos and transgenic Xenopus approaches that are ideally suited to answer these questions.
Photopic vision is mediated by cone cells, which express a protein, calleda color or cone opsin, that determines its spectral sensitivity and response characteristics. The molecular mechanisms that produce the unique properties of cone pigments are not understood. The overall goal of this project is to understand the molecular mechanisms of 11-cis-retinal/short wavelength opsin interactions that bring about their unique absorbance properties and photobleaching/ regeneration behavior; in particular, to determine how specific amino acid residues contribute to spectral tuning and phototransduction. We are biochemically characterizing the bleaching /regeneration pathway and studying the physiologically active conformation of short wavelength cone opsins using low temperature and time-resolved (>10 ns) UV-visible spectroscopy. We are investigating the role specific amino acids in violet cone opsin have in retinal interactions, photobleaching and regeneration using molecular models coupled to site-directed mutagenesis. New structural approaches to elucidate the function of these proteins are under development and to investigate structural basis of retinal disease.
Baker SA, Haeri M, Yoo P, Gospe SM 3rd, Skiba NP, Knox BE, Arshavsky VY. The outer segment serves as a default destination for the trafficking of membrane proteins in photoreceptors. J Cell Biol. 2008 Nov 3;183(3):485-98.
Danko CG, McIlvain VA, Qin M, Knox BE, Pertsov AM. Bioinformatic identification of novel putative photoreceptor specific cis-elements. BMC Bioinformatics. 2007 Oct 22;8:407.
Ramos LS, Chen MH, Knox BE, Birge RR. Regulation of photoactivation in vertebrate short wavelength visual pigments: protonation of the retinylidene Schiff base and a counterion switch. Biochemistry. 2007 May 8;46(18):5330-40. Epub 2007 Apr 18.
McIlvain VA, Knox BE. Nr2e3 and Nrl can reprogram retinal precursors to the rod fate in Xenopus retina. Dev Dyn. 2007 Jul;236(7):1970-9.