The GAF domain is a type of protein domain

Protein domain

A protein domain is a part of protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Each domain forms a compact three-dimensional structure and often can be independently stable and folded. Many proteins consist of several structural...

 that is found in a wide range of proteins from all species.
The GAF domain is named after some of the proteins it is found in: cGMP-specific phosphodiesterases, adenylyl cyclases and FhlA. The first structure of a GAF domain solved by Ho and colleagues showed that this domain shared a similar fold with the PAS domain. Many but not all GAF domains bind to cGMP

Cyclic guanosine monophosphate

Cyclic guanosine monophosphate is a cyclic nucleotide derived from guanosine triphosphate . cGMP acts as a second messenger much like cyclic AMP...

.

Examples

Human proteins containing this domain include:

• PDE2A
  PDE2A
  cGMP-dependent 3',5'-cyclic phosphodiesterase is an enzyme that in humans is encoded by the PDE2A gene.-Further reading:...
  
  , PDE5A, PDE6A
  PDE6A
  Rod cGMP-specific 3',5'-cyclic phosphodiesterase subunit alpha is an enzyme that in humans is encoded by the PDE6A gene.-External links:*...
  
  , PDE6B
  PDE6B
  Rod cGMP-specific 3',5'-cyclic phosphodiesterase subunit beta is an enzyme that in humans is encoded by the PDE6B gene.-External links:*...
  
  , PDE6C
  PDE6C
  Cone cGMP-specific 3',5'-cyclic phosphodiesterase subunit alpha is an enzyme that in humans is encoded by the PDE6C gene.- External links :* *...
  
  , PDE10A
  PDE10A
  cAMP and cAMP-inhibited cGMP 3',5'-cyclic phosphodiesterase 10A is an enzyme that in humans is encoded by the PDE10A gene.Various cellular responses are regulated by the second messengers cAMP and cGMP...
  
  , PDE10A2, PDE11A
  PDE11A
  Dual 3',5'-cyclic-AMP and -GMP phosphodiesterase 11A is an enzyme that in humans is encoded by the PDE11A gene.-Further reading:...