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The cyclic AMP response element binding protein (CREB) contains a basic leucine zipper motif (bZIP) that forms a coiled coil structure upon dimerization and specific DNA binding. Although this state is well characterized, key features of CREB bZIP binding and folding are not well understood. We used single-molecule Förster resonance energy transfer (smFRET) to probe conformations of CREB bZIP subdomains. We found differential folding of the basic region and leucine zipper in response to different binding partners; a strong and previously unreported DNA-independent dimerization affinity; folding upon binding to nonspecific DNA; and evidence of long-range interdomain interactions in full-length CREB that modulate DNA binding. These studies provide new insights into DNA binding and dimerization and have implications for CREB function., (© 2022 The Authors. FEBS Letters published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.)

Under "permissive" conditions at 25°C, the chaperonin substrate protein DM-MBP refolds 5-10 times more rapidly in the GroEL/GroES folding chamber than in free solution. This has been suggested to indicate that the chaperonin accelerates polypeptide folding by entropic effects of close confinement. Here, using native-purified DM-MBP, we show that the different rates of refolding are due to reversible aggregation of DM-MBP while folding free in solution, slowing its kinetics of renaturation: the protein exhibited concentration-dependent refolding in solution, with aggregation directly observed by dynamic light scattering. When refolded in chloride-free buffer, however, dynamic light scattering was eliminated, refolding became concentration-independent, and the rate of refolding became the same as that in GroEL/GroES. The GroEL/GroES chamber thus appears to function passively toward DM-MBP., (Copyright © 2011 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)