The GAF domain is named after some of the proteins it is found in, including cGMP-specific phosphodiesterases, adenylyl cyclases and FhlA. It is also found in guanylyl cyclases and phytochromes [1,2]. The structure of a GAF domain shows that the domain shares a similar fold with the PAS domain [3]. This domain can bind O2, CO and NO (Matilla et.al., FEMS Microbiology Reviews, fuab043, 45, 2021, 1. https://doi.org/10.1093/femsre/fuab043).

1: The GAF domain: an evolutionary link between diverse phototransducing proteins. Aravind L, Ponting CP; Trends Biochem Sci 1997;22:458-459. PMID:9433123

2: Cyclic nucleotide binding GAF domains from phosphodiesterases: structural and mechanistic insights. Heikaus CC, Pandit J, Klevit RE; Structure. 2009;17:1551-1557. PMID:20004158

3: Structure of the GAF domain, a ubiquitous signaling motif and a new class of cyclic GMP receptor. Ho YS, Burden LM, Hurley JH; EMBO J. 2000;19:5288-5299. PMID:11032796