Splice Variants of Type VIII Adenylyl Cyclase

Abstract

is the counterion for ATP. The differences in the structural and enzymatic properties of these three variants are discussed.A variety of hormones, neurotransmitters, and olfactants regulate the synthesis of cAMP by adenylyl cyclases (ACs). 1Many of these agents act through three component, G proteincoupled systems that are capable of modulating the activity of an AC (for review, see Ref. 1). Alternatively, seemingly independent signaling pathways may generate other second messengers or activate kinases that subsequently regulate AC activity by signal cross-talk. The importance of the latter class of regulatory mechanisms has become apparent with the realization that the different AC isoforms are distinguished by their ability to provide a unique integrated response to coincident stimuli.Eight full-length mammalian ACs have been characterized (2-14), and other partial cDNA sequences have been reported (15,16). The existence of additional forms which are derived by alternative splicing of the messages is consistent with the sequence differences in the amino-terminal domains encoded by cDNA clones for both type V (6, 17) and type VI (7-10). A half-molecule variant of the canine type V has been described (18), and the expression of other AC variants is suggested by the detection of multiple type V and type VIII transcripts on RNA blots under high stringency conditions (6, 9, 11, 13). Thus far, unique functional properties have not been ascribed to any specific splice variant.The mammalian ACs share a common topography. The amino-terminal domains are all predicted to be cytoplasmic, but they vary dramatically in both sequence and length. The only well conserved sequences among the ACs are found in the so-called C 1a and C 2a regions, which are two large cytoplasmic domains of over 200 amino acids each (5,19,20). The conserved domains are homologous to each other and to the catalytic domain of the guanylyl cyclases (2, 21). Based on this similarity, they are considered to be nucleotide binding domains and have recently been shown to be sufficient to confer enzymatic activity (22). Each of these domains is preceded by a large hydrophobic region of variable sequence, which includes six transmembrane spans based on hydropathy analysis. Consensus N-linked glycosylation site(s) are always present in at least one putative extracellular domain associated with the second set of six transmembrane spans (2-14). On the carboxyl-terminal side of the first putative nucleotide binding domain is a highly variable region called C 1b (5,19,20), which is a site for type-specific regulation (23-25). The corresponding region following the second nucleotide binding domain, C 2b , is only present in types I, III, and VIII (2, 4, 13). While similarities among these isoforms may underlie their common enzymatic function, their differences at the amino acid level presumably account for variable responsiveness to a variety of regulatory influences.Type VIII AC is a Ca 2ϩ /calmodulin-stimulated isoform abundantly expressed in discrete regions of...

Characterization of soluble forms of nonchimeric type V adenylyl cyclases

“…4.6.1.1) is the enzyme that converts ATP to cAMP. To date, nine distinct isoforms of mammalian AC (designated I to IX) and two splice variants of the type VIII enzyme have been cloned and characterized (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Because of the diversity in their regulation, the various AC isoforms may be broadly divided into five groups.…”

“…Because of the diversity in their regulation, the various AC isoforms may be broadly divided into five groups. Thus, group one consists of the type I, III, and VIII AC and are stimulated by calcium and calmodulin (2,4,10,13,14). The type II and IV AC constitute group two and are stimulated by ␤␥ subunits of the heterotrimeric G proteins provided that the active ␣ subunit of the stimulatory G protein (G s␣ ) is also present (3,5,15).…”

Prefractionation and separation by C8 stationary phase: Effective strategies for integral membrane proteins analysis

“…Canalicular multispecific organic anion transporter 2, an IMP with 16 TMDs, 1522 amino acids and molecular weight 168,978 Da, might be glycosylated and phosphorylated, acting as an inducible transporter in the biliary, intestinal excretion of organic anions and an alternative route for the export of bile acids and glucuronides from cholestatic hepatocytes. Adenylate cyclase type 8 with 10 TMDs, 1248 amino acids and molecular weight 168,978 Da, a membranebound, calcium-stimulable adenylyl cyclase, was revealed to be glycosylated and may be involved in learning, in memory and in drug dependence [39].…”

Biological Substrates of Operant Conditioning and the Operant—respondent Distinction

“…Bars show mean cAMP accumulation from embryonal cells expressing rat type VIII adenylyl cyclase after no treatment (basal), addition of each regulatory molecule alone, or combined treatment (both). After Cali et al (1994). gional and subcellular localization required for our molecular coincidence detector. The highest concentrations of type VIII immunoreactivity are found postsynaptically in hippocampal CA1 dendritic spines ''in intimate association with sites of calcium ion entry into the cell'' (Cooper et al, 1995, p. 421); furthermore, type VIII is the only member of the adenylyl cyclase family that responds synergistically to Ca 2ϩ and dopamine (via the stimulatory G protein, G s ) (Cali, Zwaagstra, Mons, Cooper, & Krupinski, 1994) (Figure 3).…”

“…After Cali et al (1994). gional and subcellular localization required for our molecular coincidence detector. The highest concentrations of type VIII immunoreactivity are found postsynaptically in hippocampal CA1 dendritic spines ''in intimate association with sites of calcium ion entry into the cell'' (Cooper et al, 1995, p. 421); furthermore, type VIII is the only member of the adenylyl cyclase family that responds synergistically to Ca 2ϩ and dopamine (via the stimulatory G protein, G s ) (Cali, Zwaagstra, Mons, Cooper, & Krupinski, 1994) (Figure 3). Thus, it can be anticipated that the conjunction of burst-induced Ca 2ϩ elevation and dopamine D1/D5 receptor stimulation would readily and selectively activate type VIII adenylate cyclase; the cAMP generated would need to diffuse only a short distance before activating its enzymatic target (cAMP kinase), known to be anchored in high concentrations in the same dendritic spines.…”