Structural and functional characterization of human peripheral nervous system myelin protein P2.

Viivi Majava,Francesca Natali,Inari Kursula,Eugenia Polverini,Alberto Mazzini,Peter Baumgärtel,Rahul Nanekar,Judith Peters,Petri Kursula,Wiebke Knoll

doi:10.1371/journal.pone.0010300

Abstract

The myelin sheath is a tightly packed multilayered membrane structure insulating selected axons in the central and the peripheral nervous systems. Myelin is a biochemically unique membrane, containing a specific set of proteins. In this study, we expressed and purified recombinant human myelin P2 protein and determined its crystal structure to a resolution of 1.85 Å. A fatty acid molecule, modeled as palmitate based on the electron density, was bound inside the barrel-shaped protein. Solution studies using synchrotron radiation indicate that the crystal structure is similar to the structure of the protein in solution. Docking experiments using the high-resolution crystal structure identified cholesterol, one of the most abundant lipids in myelin, as a possible ligand for P2, a hypothesis that was proven by fluorescence spectroscopy. In addition, electrostatic potential surface calculations supported a structural role for P2 inside the myelin membrane. The potential membrane-binding properties of P2 and a peptide derived from its N terminus were studied. Our results provide an enhanced view into the structure and function of the P2 protein from human myelin, which is able to bind both monomeric lipids inside its cavity and membrane surfaces.

Highlights

The myelin sheath is a multilayered membrane surrounding selected axons in the vertebrate nervous system, formed by the highly specialized plasma membrane of a myelinating glial cell
protein 2 (P2) is localized at the major dense line of myelin sheaths, and it is likely to play a similar structural role in peripheral myelin as the myelin basic protein (MBP) in both the central nervous system (CNS) and peripheral nervous system (PNS); the two proteins are, genetically and structurally unrelated
Tryptic peptide mapping by mass spectrometry of a gel band showed that the purified fractions contained human myelin P2 protein

Summary

Introduction

The myelin sheath is a multilayered membrane surrounding selected axons in the vertebrate nervous system, formed by the highly specialized plasma membrane of a myelinating glial cell. Myelin is formed of roughly 70–85% lipid, with a high content of cholesterol [1], and only 15–30% of protein, especially myelin-specific proteins. Peripheral myelin protein 2 (P2) constitutes up to 15% of total protein of peripheral nervous system (PNS) myelin [2]. P2 is localized at the major dense line of myelin sheaths, and it is likely to play a similar structural role in peripheral myelin as the myelin basic protein (MBP) in both the CNS and PNS; the two proteins are, genetically and structurally unrelated. Our recent neutron scattering experiments, have shown that upon binding to lipid bilayers, P2 decreases the lipid dynamics [7]

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Conclusion