High concentrations of D-glyceraldehyde-3-phosphate dehydrogenase stabilize the enzyme against denaturation by low concentrations of GuHCl

Dynamic oligomeric properties

This chapter provides a foundation for further research into the relationship between dynamic oligomeric properties and functional diversity. The structural basis that underlies the conformational sub-states of the GAPDH oligomer is discussed. The issue of protein stability is given a thorough analysis, since it is well-established that the primary strategy for protein oligomerization is to stabilize conformation. Several factors that affect oligomerization are described, including chemical modification by synthetic reagents. The effects of native substrates and coenzymes are also discussed. The curious feature of chloride ions having a de-stabilizing effect on native GAPDH structure is described. Additionally, the role of adenine dinucleotides in tetramer-dimer equilibrium dynamics is suggested to be a major part of the physiological regulation of GAPDH structure and function. This chapter also contends that a vast amount of useful information can come from comparative analyses of diverse species, particularly regarding protein stability and subunit-subunit interaction. Lastly, the concept of domain exchange is introduced as a means of understanding the stabilization of dynamic oligomers, suggesting that inter-subunit contacts may also be a way of masking docking sites to other proteins.

A circular dichroism and fluorescence spectrometric assessment of effects of selected chemical denaturants on soybean (Glycine max L.) storage proteins glycinin (11S) and beta-conglycinin (7S)

Soybean glycinin (11S) and beta-conglycinin (7S) were subjected to select chemical treatments at various concentrations and resulting changes in protein structures were investigated by circular dichroism (CD) and fluorescence spectrometry. Fluorescence quenching results indicated that urea >/=3 M caused significant unfolding of 11S, but not that of 7S. GuHCl was more effective than urea in denaturation of 11S. A two-step transition in 11S structure was observed with a possible existence of a folding intermediate at 2.5 M GuHCl. Sodium dodecyl sulfate (SDS) measurably altered secondary and tertiary structures of 11S and 7S below SDS critical micellar concentration (CMC), possibly due to formation of mixed peptide-SDS micelles. SDS treatment increased alpha-helical and unordered structures of both proteins at the expense of beta-sheet structure. NaCl and CaCl 2 caused a significant decrease in fluorescence intensity without shifting emission lambda max. Exposure of 7S and 11S to NaSCN respectively at >/=0.3 and >/=0.6 M NaSCN caused a significant increase in fluorescence intensity measured at the corresponding lambda max of the protein. beta-Mercaptoethanol (beta-ME), N-ethylmaleimide (NEM), and phytic acid caused variable red shifts, 2.5-4 nm, in the emission lambda max.

Effects of macromolecular crowding on the unfolding and the refolding of D-glyceraldehyde-3-phosophospate dehydrogenase

The effects of crowding agents, polyethylene glycol (PEG 20K), Dextran 70, and bovine serum albumin, on the denaturation of homotetrameric D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) in 0.5 M guanidine hydrochloride and the reactivation of the fully denatured enzyme have been examined quantitatively. Increasing the concentration of PEG 20K to 225 mg/ml decreases the rate constant of slow phase of GAPDH inactivation to 5% but with no change for the fast phase. Chaperone GroEL assists GAPDH refolding greatly and shows even higher efficiency under crowding condition. Crowding mainly affects refolding steps after the formation of the dimeric folding intermediate.