Abstract
Abstract: :
Purpose:To elucidate the structural basis for specific dimerization of photoreceptor PDE6 catalytic subunits. Methods:We constructed a series of chimeric proteins between PDE6 catalytic subunits and PDE5, containing the N-terminal GAFa and/or GAFb domains of rod or cone PDE6. These chimeras have been expressed in Sf9 cells in various combinations as His-, Myc- or Flag-tagged proteins. The dimerization of chimeric PDE6 subunits was assessed using immunoprecipitations with anti-Flag and anti-Myc specific antibodies, pull-downs with His-bind resin, and gel-filtration. Results:Our experiments indicate a preferential heterodimerization in vitro between the GAF regions of rod PDE6α and PDE6ß, and a modest dimerization of rod PDE6α with itself and cone PDE6α'. PDE6ß homodimers were formed very poorly, and PDE6 subunits did not dimerize with PDE5. Chimeric PDE subunits containing the GAFa or GAFa-GAFb domains of PDE6α dimerized with the (GAFa-GAFb) domain of PDE6ß equally well. Conclusion:The patterns of dimerization of PDE6 catalytic subunits in vitro are consistent with the selectivity of PDE6 dimerization in vivo. PDE6 GAFa domains contain major structural determinants for the affinity and selectivity of dimerization of PDE6 catalytic subunits.
Keywords: 517 photoreceptors • 527 protein structure/function • 580 signal transduction