Protein disorder: conformational distribution of the
flexible linker in a chimeric double cellulase
Ingemar von Ossowski 1, Julian T Eaton 2, Mirjam Czjzek 3, Stephen J perkins 2, Torben P Frandsen 1, Martin Schülein 1, Pierre Panine 4, Bernard Henrissat 3 and Veronique Receveur-Brechot 3*
1 Novozymes
2 University College London
3 AFMB-CNRS
4 ESRF
* To whom correspondence should be addressed. E-mail: receveur{at}afmb.cnrs-mrs.fr.
Submitted on July 21, 2004
Revised on November 9, 2004
Accepted on 16 December 2004
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Abstract |
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The structural properties of the linker peptide connecting the cellulose-binding module to the catalytic module in bimodular cellulases have been investigated by small angle X-ray scattering. Since the linker and the cellulose-binding module are relatively small and cannot be readily detected separately, the conformation of the linker was studied by means of an artificial fusion protein, Cel6BA, in which an 88 residue linker connects the large catalytic modules of the cellulases Cel6A and Cel6B from Humicola insolens. Our data showed that Cel6BA is very elongated with a maximum dimension of 178 Å, but could not be described by a single conformation. Modelling of a series of Cel6BA conformers with interdomain separations ranging between 10 Å and 130 Å showed that good Guinier and P(r) profile fits were obtained by a weighted average of the scattering curves of all the models where the linker follows a non-random distribution, with a preference for the more compact conformers. These structural properties are likely to be essential for the function of the linker as a molecular spring between the two functional modules. Small angle X-ray scattering therefore provides a unique tool to quantitatively analyse the conformational "disorder" typical of proteins described as natively unfolded.
Key Words:
cellulose, conformational disorder, distribution of conformations, linker, molecular modelling, small angle X-ray scattering
