Adenylyl cyclase (AC) is a prototypical cell signaling molecule expressed in virtually all organisms from bacteria to man. C1b, a poorly conserved region within mammalian AC, has been implicated in numerous isoform-specific regulatory properties. However, little attention has been given to this region from the perspective that it may serve as a functional regulatory subunit within the enzyme, potentially with a conserved mechanism of action across isoforms.; We hypothesize that C1b is an internal regulatory subunit. To pursue this hypothesis, we constructed several soluble C1b proteins arriving at one, 7C1b-S, which can be expressed and purified from E. coli and is relatively stable. We demonstrate that 7C1b-S interacts with the catalytic subunits of AC and with a cardinal activator of AC, Gsα. We show that 7C1b-S modestly enhances Gsα-stimulated, Gsα-forskolin stimulated and manganese-stimulated activity in our soluble ACVII model system. Based on these results, we suggest that 7C1b-S meets basic criteria to serve as a model protein for the C1b region. Reviewing these and other findings we advance a more developed hypothetical model of the C1b domain as an internal regulator of AC.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirement: Adobe Acrobat.
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