Structure, dynamics and interaction study of Glutaminase Interacting Protein (GIP) and its complex with Glutaminase L and Brain-specific Angiogenesis Inhibitor 2 (BAI2) peptide and characterization of subunit A of Heterodisulfide Reductase (HdrA) from Methanothermobacter marburgensis

Abstract

Glutaminase interacting protein (GIP) is a 124 amino acid long protein containing a single PDZ domain. This protein intersects a number of important biological pathways. In many of these pathways, the mechanism of function of this domain is still unknown. Its involvement in cancer pathways makes it a good target for drug development. We resolved the solution structures of both free GIP and GIP in complex with the C-terminal peptide analog of Glutaminase L to shed light on the mechanism of binding with the goal of future development of a potential inhibitor for GIP. To understand more of GIP’s function, interactions with two target peptides were investigated using different biophysical methods. One of the peptides was homologous to the C-terminus of brain-specific angiogenesis inhibitor 2 (BAI2) and the other one used had a consensus PDZ class I binding motif. Both of the peptides showed moderate binding affinity toward GIP with the BAI2 peptide having comparatively higher affinity. Elucidating the mechanism of interactions for different target partners would help to lay out the network of function for GIP. In a separate project, to understand the mechanism of electron bifurcation in methanogenic archaea, efforts were made to purify either heterodisulfide reductase (Hdr) or the subunit A of Hdr (HdrA) from Methanothermobacter marburgensis or Methanococcus maripaludis. We were able to purify HdrA with limited purity and showed the presence of [4Fe-4S] clusters in HdrA through EPR studies. However, efforts to purify Hdr from both organisms were with limited success. It is important to continue the efforts to obtain pure Hdr/HdrA to investigate the mechanism by which electron bifurcation takes place within this enzyme complex.