Calcium Modulation of Bovine Photoreceptor Guanylate Cyclase

Abstract

Bovine photoreceptor guanylate cyclase (ROS-GC) consists of a single transmembrane polypeptide chain with extracellular and intracellular domains. In contrast to non-photoreceptor guanylate cyclases (GCs) which are activated by hormone peptides, ROS-GC is modulated in low Ca2+ by calmodulin-like Ca(2+)-binding proteins termed GCAPs (guanylate cyclase-activating proteins). In this communication we show that, like the native system, ROS-GC expressed in COS cells is activated 4-6-fold by recombinant GCAP1 at 10 nM Ca2+ and that the reconstituted system is inhibited at physiological levels of Ca2+ (1 microM). A mutant ROS-GC in which the extracellular domain was deleted was stimulated by GCAP1 indistinguishable from native ROS-GC indicating that this domain is not involved in Ca2+ modulation. Deletion of the intracellular kinase-like domain diminished the stimulation by GCAP1, indicating that this domain is at least in part involved in Ca2+ modulation. Replacement of the catalytic domain in a non-photoreceptor GC by the catalytic domain of ROS-GC yielded a chimeric GC that was sensitive to ANF/ATP and to a lesser extent to GCAP1. The results establish that GCAP1 acts at an intracellular domain, suggesting a mechanism of photoreceptor GC stimulation fundamentally distinct from hormone peptide stimulation of other cyclase receptors.

S100B‐modulated Ca2+‐dependent ROS‐GC1 transduction machinery in the gustatory epithelium: a new mechanism in gustatory transduction

“…1C). These observed EC 50 values of all these Ca 2þ -sensor proteins for the gustatory membrane guanylate cyclase are in accord with those established earlier with the reconstituted systems consisting solely of the ROS-GC1 and individual Ca 2þ -sensor proteins [25,28,30,[38][39][40]. These results show that the anterior portion of the gustatory epithelium contains a guanylate cyclase that mimics the ROS-GC1 activity.…”

“…Other forms are defined by the composition of its two components: the Ca 2þ -sensor protein and the transducer enzyme ROS-GC (reviewed in: [26][27][28][34][35][36]45]). There are three forms of ROS-GC: ROS-GC1, ROS-GC2, and ONE-GC (also named as ret-GC1, ret-GC2 and GC-D); and four forms of the Ca 2þ -sensor proteins: GCAP1 [38], GCAP2 [45], S100B [39,40] and neurocalcin d [26,30,36]. Thus, theoretically, with the individual pairing of a sensor protein with a ROS-GC, the machine can exist in 12 different forms.…”

Calcium-sensitive Regions of GCAP1 as Observed by Chemical Modifications, Fluorescence, and EPR Spectroscopies

“…GCAP1, in contrast, is mostly associated with the membranes and/or GC1 under all [Ca 2ϩ ] (31). There are other differences between both of these proteins, most notably the sites of the GC interaction and the GC specificity (2,44,48,78). Thus, despite some similarities between these two proteins and other members of NCBP, there are important fundamental differences.…”

Calcium Binding, but Not a Calcium-Myristoyl Switch, Controls the Ability of Guanylyl Cyclase-activating Protein GCAP-2 to Regulate Photoreceptor Guanylyl Cyclase

“…Unlike peptide ligands that regulate other known membrane guanylyl cyclases via the cyclase extracellular domains (reviewed in Refs. 21 and 22), both GCAPs interact with RetGC via the cyclase intracellular domain (23,24). GCAP-1 is able to stimulate recombinant RetGC-1 (11,24), while GCAP-2 stimulates both recombinant RetGC-1 and RetGC-2 (8,19,23).…”

“…21 and 22), both GCAPs interact with RetGC via the cyclase intracellular domain (23,24). GCAP-1 is able to stimulate recombinant RetGC-1 (11,24), while GCAP-2 stimulates both recombinant RetGC-1 and RetGC-2 (8,19,23). However, the question which of the two cyclases can be a target for any particular GCAP in vivo has not yet been properly addressed.…”