Role of the C-terminal helix 9 in the stability and ligandin function of class alpha glutathione transferase A1-1.


Helix 9 at the C-terminus of class alpha glutathione transferase (GST) polypeptides is a unique structural feature in the GST superfamily. It plays an important structural role in the catalytic cycle. Its contribution toward protein stability/folding as well as the binding of nonsubstrate ligands was investigated by protein engineering, conformational stability, enzyme activity, and ligand-binding methods. The helix9 sequence displays an unfavorable propensity toward helix formation, but tertiary interactions between the amphipathic helix and the GST seem to contribute sufficient stability to populate the helix on the surface of the protein. The helix's stability is enhanced further by the binding of ligands at the active site. The order of ligand-induced stabilization increases from H-site occupation, to G-site occupation, to the simultaneous occupation of H- and G-sites. Ligand-induced stabilization of helix9 reduces solvent accessible hydrophobic surface by facilitating firmer packing at the hydrophobic interface between helix and GST. This stabilized form exhibits enhanced affinity for the binding of nonsubstrate ligands to ligandin sites (i.e., noncatalytic binding sites). Although helix9 contributes very little toward the global stability of hGSTA1-1, its conformational dynamics have significant implications for the protein's equilibrium unfolding/refolding pathway and unfolding kinetics. Considering the high concentration of reduced glutathione in human cells (about 10 mM), the physiological form of hGSTA1-1 is most likely the thiol-complexed protein with a stabilized helix9. The C-terminus region (including helix9) of the class alpha polypeptide appears not to have been optimized for stability but rather for catalytic and ligandin function. Study holds ProTherm entries: 16309 Extra Details: 1mM EDTA protein stability folding, ligand-binding, C-terminal helix 9,,alpha glutathione transferase A1-1

Submission Details


Submitter: Connie Wang

Submission Date: April 24, 2018, 8:47 p.m.

Version: 1

Publication Details
Dirr HW;Wallace LA,Biochemistry (1999) Role of the C-terminal helix 9 in the stability and ligandin function of class alpha glutathione transferase A1-1. PMID:10569948
Additional Information

Structure view and single mutant data analysis

Study data

No weblogo for data of varying length.
Colors: D E R H K S T N Q A V I L M F Y W C G P

Data Distribution

Studies with similar sequences (approximate matches)

Correlation with other assays (exact sequence matches)

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
100.0 Glutathione S-transferase A1 P08263 GSTA1_HUMAN
95.0 Glutathione S-transferase A1 P09210 GSTA2_HUMAN
90.5 Glutathione S-transferase A1 Q16772 GSTA3_HUMAN
90.1 Glutathione S-transferase A1 Q7RTV2 GSTA5_HUMAN