Attractive interhelical electrostatic interactions in the proline- and acidic-rich region (PAR) leucine zipper subfamily preclude heterodimerization with other basic leucine zipper subfamilies
Jr. Moll et al., Attractive interhelical electrostatic interactions in the proline- and acidic-rich region (PAR) leucine zipper subfamily preclude heterodimerization with other basic leucine zipper subfamilies, J BIOL CHEM, 275(44), 2000, pp. 34826-34832
Basic region-leucine zipper (B-ZIP) proteins homo- or heterodimerize to bin
d sequence-specific double-stranded DNA. We present circular dichroism (CD)
thermal denaturation data on vitellogenin promoter-binding protein (VBP),
a member of the PAR subfamily of E-ZIP proteins that also includes thyroid
embryonic factor, hepatocyte leukemia factor, and albumin site D-binding pr
otein. VBP does not heterodimerize with B-ZIP domains from C/EBP alpha, JUN
D, or FOS, We describe a dominant negative protein, A-VEP, that contains th
e VBP leucine zipper and an acidic amphipathic protein sequence that replac
es the basic region critical for DNA binding. The acidic extension forms a
coiled coil structure with the VEP basic region in the VBP A-VBP heterodime
r, This new alpha -helical structure extends the leucine zipper N-terminall
y, stabilizing the complex by 2.0 kcal/mol, A-VBP abolishes DNA binding of
VBP in an equimolar competition assay, but does not affect DNA binding even
at 100-fold excess of CREB, C/EBP alpha, or FOS/JUND, Likewise, proteins c
ontaining the acidic extension appended to seven other leucine zippers do n
ot inhibit VBP DNA binding. We show that conserved g <-> e' or i, i' + 5 sa
lt bridges are sufficient to confer specificity to VBP by mutating the C/EB
P alpha leucine zipper to contain the g <-> e' salt bridges that characteri
ze VBP, A-VBP heterodimerizes with this mutant C/EBP, preventing it from bi
nding to DNA These conserved g <-> e' electrostatic interactions define the
specificity of the PAR subfamily of B-ZIP proteins and preclude interactio
n with other B-ZIP subfamilies.