3 research outputs found
Cyclic nucleotide-binding GAF domains in phosphodiesterases and adenylyl cyclases
edition: 2ndstatus: publishe
The Structure of the GAF A Domain from Phosphodiesterase 6C Reveals Determinants of cGMP Binding, a Conserved Binding Surface, and a Large cGMP-dependent Conformational Change*Sāā¦
The photoreceptor phosphodiesterase (PDE6) regulates the intracellular
levels of the second messenger cGMP in the outer segments of cone and rod
photoreceptor cells. PDE6 contains two regulatory GAF domains, of which one
(GAF A) binds cGMP and regulates the activity of the PDE6 holoenzyme. To
increase our understanding of this allosteric regulation mechanism, we present
the 2.6Ć
crystal structure of the cGMP-bound GAF A domain of chicken
cone PDE6. Nucleotide specificity appears to be provided in part by the
orientation of Asn-116, which makes two hydrogen bonds to the guanine ring of
cGMP but is not strictly conserved among PDE6 isoforms. The isolated PDE6C GAF
A domain is monomeric and does not contain sufficient structural determinants
to form a homodimer as found in full-length PDE6C. A highly conserved surface
patch on GAF A indicates a potential binding site for the inhibitory subunit
PĪ³. NMR studies reveal that the apo-PDE6C GAF A domain is structured but
adopts a significantly altered structural state indicating a large
conformational change with rearrangement of secondary structure elements upon
cGMP binding. The presented crystal structure will help to define the
cGMP-dependent regulation mechanism of the PDE6 holoenzyme and its inhibition
through PĪ³ binding