Nonpolar lipid and phospholipid methylation during development of Dictyostelium discoideum

The biosynthesis of differentiation-inducing factor, a chlorinated signal molecule regulating Dictyostelium development

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.

S-adenosylmethionine, S-adenosylhomocysteine and S-adenosylhomocysteine hydrolase variations during differentiation of Dictyostelium discoideum

We have analyzed the level of substrate (AdoMet) and products (AdoHcy) of transmethylations throughout the developmental cycle of the primitive eukaryote Dictyostelium discoideum. The ratio AdoMet/AdoHcy varied dramatically during differentiation. The intracellular level of AdoHcy decreased sharply after the beginning of starvation reaching a value of 18% of that in vegative cells within 4 h. In contrast, there was a two-fold transient increase in AdoMet at the time of aggregation. However, these changes were not related to changes in AdoHcy hydrolase since constant levels of both the protein and the activity were found until 16 h of differentiation. In particular, there was no indication of an in vivo inactivation of the enzyme by cAMP at the time of aggregation. These results are discussed with respect to the previously postulated role of AdoHcy hydrolase in the regulation of the AdoMet/AdoHcy ratio in eukaryotic cells.