Bicarbonate activation of adenylyl cyclase via promotion of catalytic active site closure and metal recruitment.
In an evolutionarily conserved signaling pathway, 'soluble' adenylyl cyclases (sACs) synthesize the ubiquitous second messenger cyclic adenosine 3',5'-monophosphate (cAMP) in response to bicarbonate and calcium signals. Here, we present crystal structures of a cyanobacterial sAC enzyme in complex with ATP analogs, calcium and bicarbonate, which represent distinct catalytic states of the enzyme. The structures reveal that calcium occupies the first ion-binding site and directly mediates nucleotide binding. The single ion-occupied, nucleotide-bound state defines a novel, open adenylyl cyclase state. In contrast, bicarbonate increases the catalytic rate by inducing marked active site closure and recruiting a second, catalytic ion. The phosphates of the bound substrate analogs are rearranged, which would facilitate product formation and release. The mechanisms of calcium and bicarbonate sensing define a reaction pathway involving active site closure and metal recruitment that may be universal for class III cyclases.
Steegborn
Clemens
C
Department of Biochemistry, Weill Medical College of Cornell University, 1300 York Avenue, New York, New York 10021, USA.
Litvin
Tatiana N
TN
Levin
Lonny R
LR
Buck
Jochen
J
Wu
Hao
H
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001639:Bicarbonates / Q000737:chemistry / Q000494:pharmacology*; D001665:Binding Sites / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D020134:Catalytic Domain / Q000187:drug effects*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D008274:Magnesium / Q000378:metabolism*; D008322:Mammals; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013873:Thionucleotides / Q000378:metabolism
D001639:Bicarbonates; D013873:Thionucleotides; C017817:adenosine 5'-(1-thio)triphosphate; D000255:Adenosine Triphosphate; D000262:Adenylyl Cyclases; D008274:Magnesium; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium