Abstract
The multifunctional, transmembrane glycoprotein human CD38 catalyses the synthesis of three key Ca2+-mobilising messengers, including cyclic adenosine 5′-diphosphate ribose (cADPR), and CD38 knockout studies have revealed the relevance of the related signalling pathways to disease. To generate inhibitors of CD38 by total synthesis, analogues based on the cyclic inosine 5′-diphosphate ribose (cIDPR) template were synthesised. In the first example of a sugar hybrid cIDPR analogue, “L-cIDPR”, the natural “northern” N1-linked D-ribose of cADPR was replaced by L-ribose. L-cIDPR is surprisingly still hydrolysed by CD38, whereas 8-Br-L-cIDPR is not cleaved, even at high enzyme concentrations. Thus, the inhibitory activity of L-cIDPR analogues appears to depend upon substitution of the base at C-8; 8-Br-L-cIDPR and 8-NH2-L-cIDPR inhibit CD38-mediated cADPR hydrolysis (IC50 7 μM and 21 µM respectively) with 8-Br-L-cIDPR over 20-fold more potent than 8-Br-cIDPR. In contrast, L-cIDPR displays a comparative 75-fold reduction in activity, but is only ca 2-fold less potent than cIDPR itself. Molecular modelling was used to explore the interaction of the CD38 catalytic residue Glu-226 with the “northern” ribose. We propose that Glu226 still acts as the catalytic residue even for an L-sugar substrate. 8-Br-L-cIDPR potentially binds non-productively in an upside-down fashion. Results highlight the key role of the “northern” ribose in the interaction of cADPR with CD38.
Highlights
The calcium-releasing second messengers, cyclic adenosine 5′-diphosphate ribose[1] and adenosine 5′-diphosphate ribose (ADPR)[2] are synthesised in humans by CD38 from nicotinamide adenine dinucleotide (NAD+)
CADPR itself is unattractive for inhibitor design since it is readily hydrolysed at the unstable N1 link to give the linear adenosine 5′-diphosphoribose (ADPR), itself a calcium-mobilising second messenger[26,27,28]
We have previously shown that small fragments consisting of only these elements (N1-inosine 5′-monophosphates, N1-IMP), or analogues of cyclic inosine 5′-diphosphate ribose (cIDPR) with the “southern” ribose replaced by a butyl linker, inhibit cyclic adenosine 5′-diphosphate ribose (cADPR) hydrolysis by shCD38 with IC50 values in the low μM region[36,41]
Summary
The calcium-releasing second messengers, cyclic adenosine 5′-diphosphate ribose (cADPR, 1, Fig. 1)[1] and adenosine 5′-diphosphate ribose (ADPR)[2] are synthesised in humans by CD38 from nicotinamide adenine dinucleotide (NAD+). Chemo-enzymatic routes rely on Aplysia californica cyclase recognising an NAD+ analogue as a substrate and cyclising at the desired N1 position. This limits their use, for analogues that are modified at the locus of the forming N1-glycosidic bond [ see24]. CADPR forms two hydrogen bonds through N6 and N7 to Glu[146] and interacts with Glu[226] through the 2′′- and 3′′-OH of the “northern” ribose Taken together, this suggests a critical role for the base and “northern” ribose in the binding of cADPR analogues to CD38, as might be predicted for the locus of both cADPR formation and degradation. Crystallography of a hydrolysed cADPR analogue revealed that interactions with Glu[146] and Glu[226] were maintained even after hydrolysis of the N1-glycosidic bond[36]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
