文摘
The rod outer segment membrane guanylate cyclase type 1 (ROS-GC1), originally identifiedin the photoreceptor outer segments, is a member of the subfamily of Ca2+-modulated membrane guanylatecyclases. In phototransduction, its activity is tightly regulated by its two Ca2+-sensor protein parts, GCAP1and GCAP2. This study maps the GCAP2-modulatory site in ROS-GC1 through the use of multipletechniques involving surface plasmon resonance binding studies with soluble ROS-GC1 constructs,coimmunoprecipitation, functional reconstitution experiments with deletion mutants, and peptide competitionassays. The findings show that the sequence motif of the core GCAP2-modulatory site is Y965-N981 ofROS-GC1. The site is distinct from the GCAP1-modulatory site. It, however, partially overlaps with theS100B-regulatory site. This indicates that the Y965-N981 motif tightly controls the Ca2+-dependentspecificity of ROS-GC1. Identification of the site demonstrates an intriguing topographical feature ofROS-GC1. This is that the GCAP2 module transmits the Ca2+ signals to the catalytic domain from itsC-terminal side and the GCAP1 module from the distant N-terminal side.
