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Thermodynamic characterization of nucleoplasmin unfolding: interplay between function and stability
Guillermo Franco1, Sonia Bañuelos, Jorge Falces
1Unidad de Biofísica (CSIC-UPV/EHU) and Departamento de Bioquímica y Biología Molecular, Universidad del País Vasco, Apdo 644, 48080 Bilbao, Spain.
Biochemistry
|July 4, 2008
Summary
Recombinant nucleoplasmin (rNP) stability differs from natural variants. Phosphorylation destabilizes nucleoplasmin (NP), suggesting rNP
Area of Science:
- Biochemistry
- Protein Folding
- Xenopus laevis Biology
Background:
- Nucleoplasmin (NP) is a major oocyte protein involved in histone binding and chromatin assembly.
- Recombinant NP (rNP) and natural NP variants exhibit distinct biochemical properties.
- Understanding NP stability is crucial for elucidating its biological functions.
Purpose of the Study:
- To analyze the unfolding equilibrium of recombinant (rNP) and natural nucleoplasmin (NP) variants.
- To investigate the impact of phosphorylation on NP stability and unfolding.
- To compare the stability of rNP with natural NP forms isolated from Xenopus laevis.
Main Methods:
- Biochemical and spectroscopic techniques were employed.
- Chemical unfolding was induced using guanidinium salts (GuHCl, GuSCN) and urea.
- Single-carrying tryptophan mutants were used to monitor domain unfolding.
Main Results:
- Recombinant NP (rNP) pentamer unfolds and dissociates simultaneously (N 5 <--> 5U) in guanidinium salts, but not fully with urea.
- Hyperphosphorylation destabilizes the NP oligomer, with natural variants showing lower stability than nonphosphorylated rNP.
- Progressive phosphorylation correlates with a significant loss of stability (6-10 kcal/mol).
Conclusions:
- Recombinant NP (rNP) exhibits higher stability compared to natural NP variants.
- Phosphorylation-induced activation of NP leads to decreased protein stability.
- The enhanced stability of rNP may be necessary to counteract phosphorylation-induced destabilization.
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