DOUBLE-STRANDED DNA TEMPLATES CAN INDUCE ALPHA-HELICAL CONFORMATION IN PEPTIDES CONTAINING LYSINE AND ALANINE - FUNCTIONAL IMPLICATIONS FORLEUCINE-ZIPPER AND HELIX-LOOP-HELIX TRANSCRIPTION FACTORS
Np. Johnson et al., DOUBLE-STRANDED DNA TEMPLATES CAN INDUCE ALPHA-HELICAL CONFORMATION IN PEPTIDES CONTAINING LYSINE AND ALANINE - FUNCTIONAL IMPLICATIONS FORLEUCINE-ZIPPER AND HELIX-LOOP-HELIX TRANSCRIPTION FACTORS, Proceedings of the National Academy of Sciences of the United Statesof America, 91(11), 1994, pp. 4840-4844
Transcription factors of the basic-leucine zipper and basic-helix-loop
-helix families specifically recognize DNA by means of intrinsically f
lexible peptide domains that assume an alpha-helical conformation upon
binding to target DNA sequences. We have investigated the nonspecific
interactions that underlie specific DNA recognition. Circular dichroi
sm measurements showed that 20-bp double-stranded DNA oligonucleotides
can act as templates to promote random coil --> alpha-helix transitio
ns in short peptides containing alanine and lysine. This conformationa
l change takes place without altering the structure of the DNA, and ne
ither specific peptide-DNA contacts nor cooperative interactions betwe
en peptides are necessary. The conformational change does require (i)
double-stranded (but not single-stranded) oligodeoxynucleotides in eit
her the B or the B' conformation and (ii) peptides that can form posit
ively charged amphipathic alpha-helices. In 10 mM Na2HPO4 (pH 7.5; 10
degrees C), the excess free-energy contribution of the DNA template to
the stability of the alpha-helical form of the oligopeptides tested w
as Delta G(ex) = -0.15 (+/- 0.07) kcal/mol per lysine residue. The imp
lications of these results for the thermodynamics and kinetics of DNA
target site selection by basic-leucine zipper and basic-helix-loop-hel
ix regulatory proteins are discussed.