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Molecular recognition at the dimer interface of a class mu glutathione transferase: role of a hydrophobic interaction motif in dimer stability and protein function. | LitMetric

AI Article Synopsis

  • - Cytosolic glutathione transferases (GSTs) function as dimers, where interactions between subunits enhance their structural stability and functional capability, particularly at the active site and dimer interface.
  • - A specific hydrophobic motif involving phenylalanine (F56) from one subunit is crucial for maintaining dimer stability and enzymatic function; mutations at this position significantly reduce catalytic efficiency and hinder binding to ligands and substrates.
  • - While mutations at F56 do not affect the overall folding process, they alter the equilibrium between a stable dimer and a monomeric intermediate, indicating that F56 plays a key role in stabilizing the dimeric form of the enzyme.

Article Abstract

Cytosolic glutathione (GSH) transferases (GSTs) exist as stable homo- and heterodimers. Interactions at the subunit interface serve an important role in stabilizing the subunit tertiary structures of all GSH transferases. In addition, the dimer is required to maintain functional conformations at the active site on each subunit and the nonsubstrate ligand binding site at the dimer interface [Dirr, H. W. (2001) Chem.-Biol. Interact. 133, 19-23]. In this study, we report on the contribution of a specific intersubunit hydrophobic motif in rGSTM1-1 to dimer stability and protein function. The motif consists of the side chain of F56 from one subunit intercalated between helices 4 and 5 of the second subunit. Replacement of F56 with the hydrophilic side chains of serine, arginine, and glutamate results in a change in the structure of the active site, a marked diminution in catalytic efficiency, and alterations in the ability to bind nonsubstrate ligands. The mutations also affect the ability of the enzyme to bind GSH and the substrate analogue glutathione sulfonate. The functionality of rGSTM1-1 was disrupted to the greatest extent for the F56E mutant. Though mutations at this position do not alter the three-state equilibrium folding process for rGSTM1-1 (i.e., N(2) <--> 2I <--> 2U), destabilizing mutations at position 56 shift the equilibrium between the folded dimer (N(2)) and the monomeric intermediate (I) toward the latter conformational state. The transition to the unfolded state (U) is not significantly affected. The folded monomeric intermediate is also observed by electrospray ionization mass spectrometry. The amount of the intermediate is dependent on protein concentration and the residue at position 56. Mutations at position 56 have little impact on the secondary structure and stability of the monomeric folding intermediate. The dimerization process is proposed to induce a conformational change in the loop containing F56, resulting in improved stability and increased affinity between the M1 subunits.

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Source
http://dx.doi.org/10.1021/bi020548dDOI Listing

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