Editing Adenylyl cyclase (section)

=== Class I ===
{{Infobox protein family|Name=Adenylate cyclase, class-I|Symbol=Adenylate_cycl|InterPro=IPR000274|Pfam=PF01295|PROSITE=PDOC00837}}
The first class of adenylyl cyclases occur in many bacteria including ''E. coli'' (as CyaA {{UniProt|P00936}} [unrelated to the Class II enzyme]).<ref name=":2" /> This was the first class of AC to be characterized. It was observed that ''E. coli'' deprived of glucose produce cAMP that serves as an internal signal to activate expression of genes for importing and metabolizing other sugars. cAMP exerts this effect by binding the transcription factor [[cAMP receptor protein|CRP]], also known as CAP. Class I AC's are large cytosolic enzymes (~100&nbsp;kDa) with a large regulatory domain (~50&nbsp;kDa) that indirectly senses glucose levels. {{as of|2012}}, no crystal structure is available for class I AC.

Some indirect structural information is available for this class. It is known that the N-terminal half is the catalytic portion, and that it requires two Mg<sup>2+</sup> ions. S103, S113, D114, D116 and W118 are the five absolutely essential residues. The class I catalytic domain ({{Pfam|PF12633}}) belongs to the same superfamily ({{Pfam|CL0260}}) as the palm domain of [[DNA polymerase beta]] ({{Pfam|PF18765}}). Aligning its sequence onto the structure onto a related archaeal [[CCA tRNA nucleotidyltransferase]] ({{PDB|1R89}}) allows for assignment of the residues to specific functions: [[Adenosine triphosphate|γ-phosphate]] binding, structural stabilization, DxD motif for metal ion binding, and finally ribose binding.<ref>{{cite journal | vauthors = Linder JU | title = Structure-function relationships in Escherichia coli adenylate cyclase | journal = The Biochemical Journal | volume = 415 | issue = 3 | pages = 449–454 | date = November 2008 | pmid = 18620542 | doi = 10.1042/BJ20080350 }} ([https://pastebin.com/JHJeQuJn alignment])</ref>