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Jeremy M Berg

Publications and source records attributed to Jeremy M Berg.

22 records · Page 2Linked to original sources
PubMed2002

Structure-based thermodynamic analysis of a coupled metal binding-protein folding reaction involving a zinc finger peptide.

The thermodynamics of metal binding by the prototypical Cys(2)His(2) zinc finger peptide CP-1 has been examined through the use of isothermal titration calorimetry. In cholamine buffer at pH 7.0, the binding of zinc(II) to CP-1 shows an enthalpy change of DeltaH degrees (obs) = -33.7 +/- 0.8 kcal/mol. Between one and two protons appear to be released accompanying the metal binding process. The heat of protonation of the cholamine buffer used is quite large (-11.5 kcal/mol), indicating that a portion of the observed metal binding enthalpy is due to buffer protonation. Structure-based thermodynamic analysis including the effect of water release from zinc(II) appears to account for the entropy associated with the coupled metal binding-protein folding process semiquantitatively. The strongest driving force for the reaction is the enthalpy associated with the four bonds from zinc(II) to cysteinate and histidine residues, compared with the bonds from zinc(II) to water. The binding of cobalt(II) to CP-1 is less enthalpically driven than the binding of zinc(II) by -7.6 kcal/mol. This value is approximately equal to, but slightly larger than, the expectation based on considerations of ligand field stabilization energy.

Calorimetry↗
PubMed2002

PEX5 binds the PTS1 independently of Hsp70 and the peroxin PEX12.

Most peroxisomal enzymes are targeted to peroxisomes by virtue of a type-1 peroxisomal targeting signal (PTS1) at their extreme C terminus. PEX5 binds the PTS1 through its C-terminal 40-kDa tetratricopeptide repeat domain and is essential for import of PTS1-contining proteins into peroxisomes. Here we examined the PTS1-binding activity of purified, recombinant, full-length PEX5 using a fluorescence anisotropy-based assay. Like its C-terminal fragment, full-length tetrameric PEX5 exhibits high intrinsic affinity for the PTS1, with a K(d) of 35 nm for the peptide lissamine-Tyr-Gln-Ser-Lys-Leu-COO(-). The specificity of this interaction was demonstrated by the fact that PEX5 had no detectable affinity for a peptide in which the Lys was replaced with Glu, a substitution that inactivates PTS1 signals in vivo. Hsp70 has been found to regulate the affinity of PEX5 for a PTS1-containing protein, but we found that the kinetics of PEX5-PTS1 binding was unaffected by Hsp70, Hsp70 plus ATP, or Hsp70 plus ADP. In addition, we found that another protein known to interact with the PTS1-binding domain of PEX5, the PEX12 zinc RING domain, also had no discernable effect on PEX5-PTS1 binding kinetics. Taken together, these results suggest that the initial step in peroxisomal protein import, the recognition of enzymes by PEX5, is a relatively simple process and that Hsp70 most probably stimulates this process by catalyzing the folding of newly synthesized peroxisomal enzymes and/or enhancing the accessibility of their PTS1.

Adenosine Triphosphate↗
PubMed2002

Building a metal binding domain, one half at a time.

The recently determined structure of a zinc binding peptide reveals that a particular sequence can adopt one stable fold as an isolated peptide but adopt an alternative structure as part of a larger protein domain.

Carrier Proteins↗