Tài liệu Báo cáo khoa học: Solution NMR structure of an immunodominant epitope of myelin basic

Solution NMR structure of an immunodominant epitope

of myelin basic protein

Conformational dependence on environment of an intrinsically

unstructured protein

Christophe Fare` s1,*, David S. Libich1 and George Harauz1

1 Department of Molecular and Cellular Biology, and Biophysics Interdepartmental Group, University of Guelph, Canada

Multiple sclerosis is characterized by chronic inflamma￾tion of the myelin in the central nervous system (CNS),

and major variants of the illness are considered to be

primarily autoimmune in nature [1]. The 18.5 kDa

isoform of myelin basic protein (MBP) is one of the

most abundant proteins in CNS myelin; MBP maintains

the compaction of the sheath by anchoring the cytoplas￾mic faces of the oligodendrocyte membranes [2], and is a

candidate antigen for T cells and autoantibodies in

multiple sclerosis [3]. The three-dimensional structure of

MBP has not yet been elucidated to high resolution

[4,5]. We recently used site-directed spin-labeling

Keywords

correlation spectroscopy; multiple sclerosis;

myelin basic protein; immunodominant

epitope; solution NMR

Correspondence

G. Harauz, Department of Molecular and

Cellular Biology, and Biophysics

Interdepartmental Group, University of

Guelph, 50 Stone Road East, Guelph,

Ontario, Canada, N1G 2W1

Fax: +1 519 837 2075

Tel: +1 519 824 4120, ext. 52535

E-mail: [email protected]

*Present address

Max-Planck-Institut fu¨r Biophysikalische

Chemie, NMR-Based Structural Biology,

Go¨ttingen, Germany.

Christophe Fare` s and David S. Libich contri￾buted equally to this work.

(Received 19 October 2005, revised

1 December 2005, accepted 7 December

2005)

doi:10.1111/j.1742-4658.2005.05093.x

Using solution NMR spectroscopy, three-dimensional structures have been

obtained for an 18-residue synthetic polypeptide fragment of 18.5 kDa

myelin basic protein (MBP, human residues Q81–T98) under three condi￾tions emulating the protein’s natural environment in the myelin membrane

to varying degrees: (a) an aqueous solution (100 mm KCl pH 6.5), (b) a

mixture of trifluoroethanol (TFE-d2) and water (30 : 70% v ⁄ v), and (c) a

dispersion of 100 mm dodecylphosphocholine (DPC-d38, 1 : 100 pro￾tein ⁄ lipid molar ratio) micelles. This polypeptide sequence is highly con￾served in MBP from mammals, amphibians, and birds, and comprises a

major immunodominant epitope (human residues N83–T92) in the auto￾immune disease multiple sclerosis. In the polypeptide fragment, this epitope

forms a stable, amphipathic, a helix under organic and membrane-mimetic

conditions, but has only a partially helical conformation in aqueous solu￾tion. These results are consistent with recent molecular dynamics simula￾tions that showed this segment to have a propensity to form a transient

a helix in aqueous solution, and with electron paramagnetic resonance

(EPR) experiments that suggested a a-helical structure when bound to a

membrane [I. R. Bates, J. B. Feix, J. M. Boggs & G. Harauz (2004) J Biol

Chem, 279, 5757–5764]. The high sensitivity of the epitope structure to its

environment is characteristic of intrinsically unstructured proteins, like

MBP, and reflects its association with diverse ligands such as lipids and

other proteins.

Abbreviations

CNS, central nervous system; CSI, chemical shift index; DIPSI, decoupling in the presence of scalar interactions; DPC-d38, perdeuterated

dodecylphosphatidylcholine; DSA, doxylstearic acid; EPR, electron paramagnetic resonance; Fmoc, 9-fluorenylmethoxycarbonyl; gpMBP,

guinea pig myelin basic protein; hMBP, human myelin basic protein; MAP, mitogen-activated protein; MBP, myelin basic protein; MHC,

major histocompatibility complex; rmMBP, recombinant murine; RMSD, root mean squared deviation; SDSL, site-directed spin-labeling; SH3,

Src homology domain 3; TFE-d2, deuterated 2,2,2-trifluoroethanol (CF3-CD2-OH); TSP, 3-(trimethylsilyl)-propionic acid.

FEBS Journal 273 (2006) 601–614 ª 2006 The Authors Journal compilation ª 2006 FEBS 601