Stavros P, Malecki PH, Theodoridou M, Rypniewski W, Vorgias CE, Nounesis G. The stability of the TIM-barrel domain of a psychrophilic chitinase.
Biochem Biophys Rep 2015;
3:108-116. [PMID:
29124173 PMCID:
PMC5668695 DOI:
10.1016/j.bbrep.2015.07.016]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 07/24/2015] [Accepted: 07/28/2015] [Indexed: 11/22/2022] Open
Abstract
Chitinase 60 from the psychrophilic bacterium Moritella marina (MmChi60) is a four-domain protein whose structure revealed flexible hinge regions between the domains, yielding conformations in solution that range from fully extended to compact. The catalytic domain is a shallow-grooved TIM-barrel. Heat-induced denaturation experiments of the wild-type and mutants resulting from the deletions of the two-Ig-like domains and the chitin binding domain reveal calorimetric profiles that are consistent with non-collaborative thermal unfolding of the individual domains, a property that must be associated to the “hinge-regions”. The calorimetric measurements of the (β/α)8 catalytic domain reveal that the thermal unfolding is a slow-relaxation transition exhibiting a stable, partially structured intermediate state. Circular dichroism provides evidence that the intermediate exhibits features of a molten globule i.e., loss of tertiary structure while maintaining the secondary structural elements of the native. GdnHCl-induced denaturation studies of the TIM-barrel demonstrate an extraordinarily high resistance to the denaturant. Slow-relaxation kinetics characterize the unfolding with equilibration times exceeding six days, a property that is for the first time observed for a psychrophilic TIM barrel. On the other hand, the thermodynamic stability is ΔG=6.75±1.3 kcal/mol, considerably lower than for structural-insertions-containing barrels. The mutant E153Q used for the crystallographic studies of MmChi60 complexes with NAG ligands has a much lower stability than the wild-type.
We use heat-induced and chemical denaturation to study MmChi60.
The impact of “hinge” regions upon the DSC calorimetric profiles is explored.
CD is used to characterize the thermal unfolding intermediate of the catalytic domain.
The thermodynamic stability of the TIM-barrel is measured via chemical denaturation.
High-resistance to denaturants is evidenced for the psychrophilic (β/α)8 domain.
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