THE STRUCTURAL ANALYSIS OF PHOTO-TRANSDUCTION PROTEINS

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The aim of this international cooperative research with Dr Akio Yamazaki, Kresge Eye Institute, Wayne State University, was to reveal morphological counterpart of the photo-transduction process in the vertebrate photoreceptor cells. In 1998, we have investigated morphological change of phosphodiesterase (PDE), one of the key components in phototransduction, accompanied by functional changes in PDE subunits and to elucidate new roles of PDE in visual signal transduction mechanism. In contrast to significant progress in understanding the flow of signals in phototransduction and the roles of each component in the flow of signals, the relationship in PDE subunits is unknown because of difficulty of purification and expression of intact Pαβ and lack of information about regulation of Pαβ-Pγinteractions. However, in this study, Pαβ-Pγ interactions were partially elucidated with new findings on the mechanism of Pγ modifications and unexpected finding on the PDE role in the increase of cytoplasmic cGMP level in rod outer segments. Our recent development in the isolation and purification of bovine Pαβ with or without Pγ also made possible to observe the molecules under electron microscope. All types of PDE (αβγγ, αβγ, αβ) consisted basically of two crooked strands with characteristic shape that were arranged as making a ring. Suggestible structural changes induced by dislocation of Pγ from complete PDE were arrested as three dimensional shift of molecules in position. In 1999, we started to study the functional structure of synaptic ribbons that are located at the active site and surrounded by a halo of synaptic vesicles. Our new electron microscopy revealed surprisingly that synaptic ribbon was associated with Ca. Since synaptic ribbon represented abundant phosphorus element signals in electron energy loss spectral imaging, it is clear that the synaptic ribbon is a derivative of the membrane.