The NMR solution structure of the ubiquitin homology domain of Bcl-2-associated athanogene 1 (BAG-1-UBH) from Mus musculus

Abstract

BAG-1 (Bcl-2-associated athanogene 1), a multifunctional anti-apoptotic protein known to interact with various cellular proteins, was isolated using its interaction with the anti-apoptotic protein, Bcl-2. A 97-amino acid segment that includes the ubiquitin homology (UBH) domain of mouse BAG-1 (mBAG-1) interacts with a peptide corresponding to the cytoplasmic tail (CT) domain of proHB-EGF. This protein–peptide interaction is likely to have functional significance, as the two species exhibit a synergistic cytoprotective effect. In this study, we determined the solution structure of mBAG-1-UBH and investigated its interaction with the proHB-EGF-CT peptide using isothermal titration calorimetry and NMR spectroscopy. The solution structure of mBAG-1-UBH was shown to be similar to the previously reported structure of hBAG-1-UBH (PDB code 1WXV). However, their electrostatic potential maps demonstrated some differences in the UBH motifs that may be important for protein–peptide interaction. An NMR titration experiment demonstrated that residues 23–26 and residues 89–94 of mBAG-1-UBH are important for its molecular interaction with the peptide proHB-EGF-CT. BAG-1-UBH shares some biological functions with ubiquitin including the formation of polyubiquitin chain and the proteasomal protein degradation. The unique cytoprotective activity suggests mBAG-1-UBH to be an interesting ubiquitin-like protein with distinct biological functions. Here, we first reported the solution structure of mBAG-1-UBH and the growth factor precursor-interacting motif on the protein. For detail understanding about the binding interface and the mechanism of interaction, the study on mBAG-1-UBH/proHB-EGF-CT complex structure is necessary.