The structure of a CREB bZIP.somatostatin CRE complex reveals the basis for selective dimerization and divalent cation-enhanced DNA binding.
The cAMP responsive element-binding protein (CREB) is central to second messenger regulated transcription. To elucidate the structural mechanisms of DNA binding and selective dimerization of CREB, we determined to 3.0 A resolution, the structure of the CREB bZIP (residues 283-341) bound to a 21-base pair deoxynucleotide that encompasses the canonical 8-base pair somatostatin cAMP response element (SSCRE). The CREB dimer is stabilized in part by ionic interactions from Arg(314) to Glu(319') and Glu(328) to Lys(333') as well as a hydrogen bond network that links the carboxamide side chains of Gln(322')-Asn(321)-Asn(321')-Gln(322). Critical to family selective dimerization are intersubunit hydrogen bonds between basic region residue Tyr(307) and leucine zipper residue Glu(312), which are conserved in all CREB/CREM/ATF-1 family members. Strikingly, the structure reveals a hexahydrated Mg(2+) ion bound in the cavity between the basic region and SSCRE that makes a water-mediated DNA contact. DNA binding studies demonstrate that Mg(2+) ions enhance CREB bZIP:SSCRE binding by more than 25-fold and suggest a possible physiological role for this ion in somatostatin cAMP response element and potentially other CRE-mediated gene expression.
Schumacher
M A
MA
Department of Biochemistry and Molecular Biology and the Vollum Institute, Oregon Health Sciences University, Portland, Oregon 97201-3098, USA.
Goodman
R H
RH
Brennan
R G
RG
D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry; D001216:Asparagine / Q000737:chemistry; D002412:Cations / Q000378:metabolism*; D018360:Crystallography, X-Ray; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry* / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D004583:Electrons; D004926:Escherichia coli / Q000378:metabolism; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D006860:Hydrogen Bonding; D007477:Ions; D007700:Kinetics; D016350:Leucine Zippers; D008239:Lysine / Q000737:chemistry; D008274:Magnesium / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D020218:Response Elements; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013004:Somatostatin / Q000737:chemistry* / Q000378:metabolism*
D002412:Cations; D017362:Cyclic AMP Response Element-Binding Protein; D004268:DNA-Binding Proteins; D007477:Ions; D005973:Glutamine; D018698:Glutamic Acid; D013004:Somatostatin; D001216:Asparagine; D004247:DNA; D001120:Arginine; D008274:Magnesium; D008239:Lysine