Abstract
Differentiation-inducing factor (DIF)-1 is a chlorinated alkyl phenone released by developing Dictyostelium amoebae, which induces them to differentiate into stalk cells. A biosynthetic pathway for DIF-1 is proposed from labeling, inhibitor, and enzymological experiments. Cells incorporate 36Cl- into DIF-1 during development, showing that the chlorine atoms originate from chloride ions; peak incorporation is at the first finger stage. DIF-1 synthesis can be blocked by cerulenin, a polyketide synthase inhibitor, suggesting that it is made from a polyketide. This is most likely the C12 polyketide (2,4,6-trihydroxyphenyl)-1-hexan-1-one (THPH). Feeding experiments confirm that living cells can convert THPH to DIF-1. Conversion requires both chlorination and methylation of THPH, and enzymatic activities able to do this exist in cell lysates. The chlorinating activity, assayed using 36Cl-, is stimulated by H2O2 and requires both soluble and particulate components. It is specific for THPH and does not use this compound after O-methylation. The methyltransferase is soluble, uses S-adenosyl-L-methionine as a co-substrate, has a Km for dichloro-THPH of about 1.1 microM, and strongly prefers this substrate to close analogues. Both chlorinating and methyltransferase activities increase in development in parallel with DIF-1 production, and both are greatly reduced in a mutant strain that makes little DIF-1. It is proposed that DIF-1 is made by the initial assembly of a C12 polyketide skeleton, which is then chlorinated and methylated.
Highlights
This paper is dedicated to the memory of the late Dr Mary Berks, good friend and colleague
To understand this process further requires a better knowledge of Differentiation-inducing factor (DIF)-1 signaling and, to this end, I have attempted to discover the biosynthetic pathway for DIF-1
One is DIF-1, as shown by co-chromatography on two different TLC systems and by the previous demonstration of DIF-1 in slug extracts by HPLC [43]; the other compound (X) is unidentified. This compound runs in approximately the same place on TLC as dichloro-THPH, a proposed precursor of DIF-1 (Fig. 8), but further characterization was not attempted due to the low amounts present
Summary
This paper is dedicated to the memory of the late Dr Mary Berks, good friend and colleague. These cells rapidly produce DIF-1 dechlorinase, which inactivates DIF-1 and prevents a further rise in levels, allowing the majority of cells to differentiate as prespores [11, 12] To understand this process further requires a better knowledge of DIF-1 signaling and, to this end, I have attempted to discover the biosynthetic pathway for DIF-1. The aromatic ring of DIF-1 could arise either from the shikimate pathway of aromatic amino acid biosynthesis [17] or from a polyketide Of these alternatives, a polyketide origin for DIF-1 is the more likely, since it automatically explains the four alternating oxysubstitutions of the final molecule [18] and because this is the way that many simple aromatic metabolites are made, including acetylphloroglucinol [19], a homologue of the proposed polyketide precursor of DIF-1. Polyketide synthases usually combine the activities required for polyketide synthesis
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