Kinetics of folding and unfolding of goat alpha-lactalbumin.


Abstract

The equilibrium unfolding and the kinetic folding and unfolding of goat alpha-lactalbumin (GLA) were studied by near- and far-ultraviolet circular dichroism (CD) and by stopped-flow fluorescence spectroscopy. Specifically, the influence of environmental conditions such as pH and Ca2+ binding was examined. Compared to the apo-form, the Ca2+-bound form was found to be strongly stabilized in equilibrium conditions at pH 7.5 and 25 degrees C. The kinetics of the refolding of apo-GLA show a major change of fluorescence intensity during the experimental dead-time, but this unresolved effect is strongly diminished in holo-GLA. In both cases, however, the chevron plots can adequately be fitted to a three-state model. Moreover, double-mix stopped-flow experiments showed that the native state (N) is reached through one major pathway without the occurrence of alternative tracks. In contrast to the homologous bovine alpha-lactalbumin (BLA), the compactness of GLA is strongly influenced by the presence of Ca2+ ions. Unlike the two-state transition observed in guanidine hydrochloride (GdnHCl)-induced equilibrium denaturation experiments at higher pH, an equilibrium intermediate state (I) is involved in denaturation at pH 4.5. In the latter case, analysis of the kinetic data makes clear that the intermediate and the unfolded states (U) show practically no Gibbs free energy difference and that they are in rapid equilibrium with each other. A possible explanation for these variations in stability and in folding characteristics with pH could be the degree of protonation of His107 that directly influences non-native interactions. Variation of environmental conditions and even small differences in sequence, therefore, can result in important effects on thermodynamic and folding parameters. Study holds ProTherm entries: 18215, 18216, 18217, 18218, 18219, 18220 Extra Details: 2mM EDTA was added in the experiment lactalbumin; stopped-flow fluorescence spectroscopy; kinetics; protein folding; intermediate state; circular dichroism; lysozyme

Submission Details

ID: t6EmBd233

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:50 p.m.

Version: 1

Publication Details
Chedad A;Van Dael H,Proteins (2004) Kinetics of folding and unfolding of goat alpha-lactalbumin. PMID:15340922
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 PDB Entries

Structure ID Release Date Resolution Structure Title
3B0K 2012-06-13 1.6 Crystal structure of alpha-lactalbumin
1FKQ 2001-02-14 1.8 RECOMBINANT GOAT ALPHA-LACTALBUMIN T29V
6IP9 2019-02-20 1.85 Crystal Structure of Lanthanum ion (La3+) bound bovine alpha-lactalbumin
1HMK 1999-11-26 2.0 RECOMBINANT GOAT ALPHA-LACTALBUMIN
1FKV 2001-02-14 2.0 RECOMBINANT GOAT ALPHA-LACTALBUMIN T29I
1F6S 2000-12-13 2.2 CRYSTAL STRUCTURE OF BOVINE ALPHA-LACTALBUMIN
1F6R 2000-12-13 2.2 CRYSTAL STRUCTURE OF APO-BOVINE ALPHA-LACTALBUMIN
2G4N 2007-02-20 2.3 Anomalous substructure of alpha-lactalbumin
1HFZ 1997-07-29 2.3 ALPHA-LACTALBUMIN
1HFY 1997-07-07 2.3 ALPHA-LACTALBUMIN

Relevant UniProtKB Entries

Percent Identity Matching Chains Protein Accession Entry Name
94.4 Alpha-lactalbumin Q9TSR4 LALBA_BOSMU
95.1 Alpha-lactalbumin P00711 LALBA_BOVIN
96.5 Alpha-lactalbumin Q9TSN6 LALBA_BUBBU
97.9 Alpha-lactalbumin P09462 LALBA_SHEEP
100.0 Alpha-lactalbumin P00712 LALBA_CAPHI