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Dictyostelium main pageLinks are provided to files on the P450 server. Some text summarizing the findings is given.

The ancient model organism Dictyostelium discoideum (cellular slime mold) has at least 55 different P450 genes. See the alignment above. These include a CYP51sequence. CYP524A1 may be the ortholog of CYP61 in fungi. The other sequencesshow no close resemblance to other eukaryotic P450s and they probably evolved independently from the CYP51 sequence. A tree of these sequences (linked above) suggests they fall into 15 families. Assembly of the genes from genomic DNA sequence has resulted in assembly of 42 complete P450 genes that probably code for proteins. There are three full length pseudogenes and 10 incomplete pseudogenes. See the reconciled assemblies file above.Very little is known about the P450 functions in Dicty, however a mutation called RedA in the P450 reductase blocks stalk formation. Stalk formation is dependent on a signaling molecule called DIF-1. This is a hydrophobic chlorinated, hydroxylated compound, a prime candidate for a P450 to act on. Recent work has shown that one and maybe three P450s act in the degradation of DIF-1. DIF-1 is dehalogenated to a molecule called DIF-3 and P450s oxidize this molecule. An abstract of a paper from the Dicty database is shown below.The proximal pathway of metabolism of the chlorinated signal moleculeDIF-1 in DictyosteliumPiero Morandini, John Offer, David Traynor, Oliver Nayler, DavidNeuhaus, Graham W. Taylor* and Robert R. Kay MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH,UK *Department of Clinical Pharmacology, Royal Postgraduate MedicalSchool, London W12 OHS. Present addresses. PM: Dipartimento di Biologia ‘L. Gorini”, viaCeloria 26, 20133 Milano, Italy. DT: Department of Pharmacology,University of Cambridge, Tennis Court Rd, Cambridge CB2 1QJ, UKBiochemical J., in press.Abstract Stalk cell differentiation during Dictyostelium development isinduced by a chlorinated alkyl phenone called DIF-1. Inactivation ofDIF-1 is likely to be a key element in the DIF-1 signalling system andwe have shown previously that this is accomplished by a dedicatedmetabolic pathway involving up to a dozen unidentified metabolites.We report here the structure of the first four metabolites producedfrom DIF-1, as deduced by mass spectroscopy, NMR and chemicalsynthesis. The structures of these compounds show that the first stepin metabolism is a dechlorination of the phenolic ring, producing DM1.DM1 is identical with the previously known minor DIF activity, DIF-3.DIF-3 is then metabolised by three successive oxidations of itsaliphatic side chain: a hydroxylation at w-2 to produce DM2, oxidationof the hydroxyl to a ketone to produce DM3 and a further hydroxylationat w-1 to produce DM4, a hydroxy ketone of DIF-3. We haveinvestigated the enzymology of DIF-1 metabolism. It is already knownthat the first step, to produce DIF-3, is catalysed by a noveldechlorinase. The enzyme activity responsible for the first sidechain oxidation was detected by incubating 3H-DIF-3 with cell-freeextracts and resolving the reaction products by TLC. It will bereferred to as DIF-3 hydroxylase. DIF-3 hydroxylase has many of theproperties of a cytochrome P450. It is membrane bound and uses NADPHas co-substrate. It is also inhibited by carbon monoxide, the classicP450 inhibitor, and by several other P450 inhibitors as well as bydiphenyliodonium chloride, an inhibitor of cytochrome P450 reductase.DIF-3 hydroxylase is highly specific for DIF-3: other closely relatedcompounds do not compete for the activity at 100-fold molar excess,except for a DIF-3 analog lacking the chlorine atom. The Km for DIF-3of 47nM is consistent with this enzyme being responsible for DIF-3metabolism in vivo. The two further oxidations necessary to produceDM4 are also performed in vitro by similar enzyme activities. One ofthe inhibitors of DIF-3 hydroxylase, ancymidol (IC50=67nM) will beparticularly suitable for probing the function of DIF metabolismduring development.