Structure, Mechanism, and Regulation of Mammalian Adenylyl Cyclase

Abstract

stimulatory G-protein α subunit inhibitory G-protein α subunit G-protein βγ subunit Ca2+/calmodulin-dependent protein kinase The discovery of 3′,5′-cyclic adenosine monophosphate (cAMP) in the late 1950s by Sutherland and co-workers was the pivotal event that led to our current paradigm of hormone signaling through second messengers. Despite the subsequent discovery of many other second messengers, cAMP has never left center stage. The adenylyl cyclases are the family of enzymes that synthesize cAMP (1Sunahara R.K. Dessauer C.W. Gilman A.G. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 461-480Crossref PubMed Scopus (732) Google Scholar, 2Xia Z.G. Storm D.R. Curr. Opin. Neurobiol. 1997; 7: 391-396Crossref PubMed Scopus (122) Google Scholar, 3Hanoune J. Pouille Y. Tzavara E. Shen T.S. Lipskaya L. Miyamoto N. Suzuki Y. Defer N. Mol. Cell. Endocrinol. 1997; 128: 179-194Crossref PubMed Scopus (139) Google Scholar, 4Cooper D.M.F. Adv. Second Messenger Phosphoprotein Res. 1998; : 32Google Scholar, 5Tang W.-J. Hurley J.H. Mol. Pharmacol. 1998; 54: 231-240Crossref PubMed Scopus (160) Google Scholar).Breakthroughs in determining the first structures of the mammalian adenylyl cyclase catalytic core (6Zhang G. Liu Y. Ruoho A.E. Hurley J.H. Nature. 1997; 386: 247-253Crossref PubMed Scopus (323) Google Scholar, 7Tesmer J.J.G. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (670) Google Scholar) provide a new context for understanding the action of many regulators, both physiological and pharmacological: free metal ions, P-site inhibitors, forskolin, G-proteins, Ca2+/calmodulin, and protein phosphorylation. Understanding the catalytic mechanism of an enzyme is a prerequisite to understanding its regulation. Here I will describe the essentials of catalysis and then consider how these elements are controlled by each of the major regulators.Structure of Adenylyl CyclaseThe nine cloned isoforms of mammalian adenylyl cyclase share a primary structure consisting of two transmembrane regions, M1 and M2, and two cytoplasmic regions, C1 and C2 (8Krupinski J. Coussen F. Bakalyar H. Tang W.-J. Feinstein P.G. Orth K. Slaughter C. Reed R.R. Gilman A.G. Science. 1989; 244: 1558-1564Crossref PubMed Scopus (505) Google Scholar) (Fig.1). The transmembrane regions each contain six predicted membrane-spanning helices. The function of M1 and M2, aside from membrane localization, is unknown despite their topological analogy to transporters. The C1 and C2 regions are subdivided into C1a and C1b; and C2a and C2b. The C1a and C2a are well conserved, homologous to each other, and contain all of the catalytic apparatus (9Tang W.-J. Gilman A.G. Science. 1995; 268: 1769-1772Crossref PubMed Scopus (165) Google Scholar). C1a and C2a domains heterodimerize with each other in solution (10Yan S.-Z. Hahn D. Huang Z.-H. Tang W.-J. J. 1996; PubMed Scopus Google Scholar, Gilman A.G. Dessauer C.W. 1996; PubMed Scopus Google Scholar). domains from isoforms The is and The is in isoforms and C2 and C2a are to structure of the adenylyl cyclase C2 a with two C2 in a (6Zhang G. Liu Y. Ruoho A.E. Hurley J.H. Nature. 1997; 386: 247-253Crossref PubMed Scopus (323) Google Scholar). the two in the center of the to in the The is that the the The is the is to the domains of the I and Nature. 1997; PubMed Scopus Google Scholar, J. Liu Y. Ruoho A.E. G. Hurley J.H. Nature. 1997; Scopus Google C1a and C2 in a that is in structure to the C2 with in J.J.G. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (670) Google Scholar). The is of the The by C.W. Gilman A.G. J. 1997; PubMed Scopus Google is the The is the by by both C1a and the is the two of two catalytic domains in the is an prerequisite of catalytic The of mammalian adenylyl cyclases the of C1a and is the for many other cyclases Y. Ruoho A.E. Hurley J.H. 1997; PubMed Scopus Google Scholar, J.H. Curr. Opin. 1998; PubMed Scopus Google Scholar). membrane cyclases and many of mammalian adenylyl cyclases are The mammalian C2 has (9Tang W.-J. Gilman A.G. Science. 1995; 268: 1769-1772Crossref PubMed Scopus (165) Google Scholar, G. Liu Y. J. Tang W.-J. Ruoho A.E. Hurley J.H. 1997; PubMed Scopus Google Scholar, Tang W.-J. C. 1998; PubMed Scopus Google by many of of the of two catalytic to the and has by the structure of the P-site J.J.G. Sunahara R.K. Gilman A.G. Sprang S.R. Science. 1997; 278: 1907-1916Crossref PubMed Scopus (670) Google Y. Ruoho A.E. Hurley J.H. 1997; PubMed Scopus Google and Y. Ruoho A.E. Hurley J.H. 1997; PubMed Scopus Google Scholar, W.-J. Gilman A.G. 1995; PubMed Scopus Google Scholar, S.-Z. Huang Z.-H. Tang W.-J. J. 1997; PubMed Scopus Google Scholar, Hurley J.H. Hurley 1998; PubMed Scopus Google Scholar, R.K. J.J.G. Sprang S.R. Gilman A.G. J. 1998; PubMed Scopus Google Scholar). the is is for and from C2 with the and of the of C1 a by the of these the of adenylyl into a cyclase R.K. J.J.G. Sprang S.R. Gilman A.G. J. 1998; PubMe