The intrinsically disordered RNR inhibitor Sml1 is a dynamic dimer

Jens Danielsson, Leena Liljedahl, Elsa Ba´ra´ny-Wallje, Pernille Sønderby, Line Hyltoft Kristensen, Maria A Martinez-Yamout, H Jane Dyson, Peter E Wright, Flemming M Poulsen, Lena Ma¨ler, Astrid Gra¨slund, Birthe B Kragelund

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50 Citationer (Scopus)

Abstract

Sml1 is a small ribonucleotide reductase (RNR) regulatory protein in Saccharomyces cerevisiae that binds to and inhibits RNR activation. NMR studies of (15)N-labeled Sml1 (104 residues), as well as of a truncated variant (residues 50-104), have allowed characterization of their molecular properties. Sml1 belongs to the class of intrinsically disordered proteins with a high degree of dynamics and very little stable structure. Earlier suggestions for a dimeric structure of Sml1 were confirmed, and from translation diffusion NMR measurements, a dimerization dissociation constant of 0.1 mM at 4 degrees C could be determined. The hydrodynamic radius for the monomeric form of Sml1 was determined to be 23.4 A, corresponding to a protein size between those of a globular protein and a coil. Formation of a dimer results in a hydrodynamic radius of 34.4 A. The observed chemical shifts showed in agreement with previous studies two segments with transient helical structure, residues 4-20 and 60-86, and relaxation studies clearly showed restricted motion in these segments. A spin-label attached to C14 showed long-range interactions with residues 60-70 and 85-95, suggesting that the N-terminal domain folds onto the C-terminal domain. Importantly, protease degradation studies combined with mass spectrometry indicated that the N-terminal domain is degraded before the C-terminal region and thus may serve as a protection against proteolysis of the functionally important C-terminal region. Dimer formation was not associated with significant induction of structure but was found to provide further protection against proteolysis. We propose that this molecular shielding and protection of vital functional structures from degradation by functionally unimportant sites may be a general attribute of other natively disordered proteins.
OriginalsprogEngelsk
TidsskriftBiochemistry
Vol/bind47
Udgave nummer50
Sider (fra-til)13428-13437
Antal sider9
ISSN0006-2960
DOI
StatusUdgivet - 2008

Bibliografisk note

Keywords: Amino Acid Sequence; Conserved Sequence; Dimerization; Molecular Sequence Data; Peptide Fragments; Protein Binding; Protein Structure, Tertiary; Ribonucleotide Reductases; Saccharomyces cerevisiae Proteins; Thermodynamics

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