Characterization of the amino-terminal activation domain of peroxisome proliferator-activated receptor alpha - Importance of alpha-helical structure in the transactivating function

The transactivating function of the A/B region of mouse peroxisome prolifer ator-activated receptor alpha (PPAR alpha; NR1C1) was characterized. The tr uncated version of PPAR alpha lacking the A/B region had 60-70% lower trans activating function than full-length PPAR alpha in both the presence and ab sence of the peroxisome proliferator ciprofibrate. When tethered to the yea st Gal4 DNA-binding domain, the A/B region exhibited the significant ligand -independent transactivating function, AF-1 activity. The first 44 amino ac id residues were necessary for maximal transactivation, and the minimally e ssential region was further delimited to amino acids 15-44. This region is highly enriched with acidic residues, but mutational analyses showed that t he protein structure, rather than the negative charge itself, was important for the AF-1 activity. An alpha-helical configuration was predicted for th is region, and a CD spectrum analysis of the synthetic peptides showed that mutant sequences with higher AF-1 activity have higher helical contents an d vice versa. The most active mutant, in which Met(31) was replaced with Le u, was similar to 5-fold more potent than the wild-type A/B region. These f indings indicate that the AF-1 region of PPAR alpha is an acidic activation domain and that the helix-forming property is implicated in the transactiv ating function.