Human myelin protein P2: from crystallography to time‐lapse membrane imaging and neuropathy‐associated variants

Abstract

Peripheral myelin protein 2 (P2) is a fatty acid-binding protein expressed in vertebrate peripheral nervous system myelin, as well as in human astrocytes. Suggested functions of P2 include membrane stacking and lipid transport. Mutations in the PMP2 gene, encoding P2, are associated with Charcot-Marie-Tooth disease (CMT). Recent studies have revealed three novel PMP2 mutations in CMT patients. To shed light on the structure and function of these P2 variants, we used X-ray and neutron crystallography, small-angle X-ray scattering, circular dichroism spectroscopy, computer simulations and lipid binding assays. The crystal and solution structures of the I50del, M114T and V115A variants of P2 showed minor differences to the wild-type protein, whereas their thermal stability was reduced. Vesicle aggregation assays revealed no change in membrane stacking characteristics, while the variants showed altered fatty acid binding. Time-lapse imaging of lipid bilayers indicated formation of doublemembrane structures induced by P2, which could be related to its function in stacking of two myelin membrane surfaces in vivo. In order to better understand the links between structure, dynamics and function, the crystal structure of perdeuterated P2 was refined from room temperature data using neutrons and X-rays, and the results were compared to simulations and cryocooled crystal structures. Our data indicate similar properties for all known human P2 CMT variants; while crystal structures are nearly identical, thermal stability and function of CMT variants are impaired. Our data provide new insights into the structure-function relationships and dynamics of P2 in health and disease.

Conservation and divergence of myelin proteome and oligodendrocyte transcriptome profiles between humans and mice

“…For example, we noted that peripheral myelin protein 2 (PMP2, also termed P2 or fatty acid binding protein [FABP8]) was identified in human CNS myelin ( Figure 2b ). PMP2 has long been known as a constituent of myelin in the peripheral nervous system (PNS) synthesized by Schwann cells ( Greenfield et al, 1973 ; Uusitalo et al, 2021 ) but based on rodent studies was assumed to be absent from CNS myelin. Yet, PMP2 was readily detected in human CNS myelin by both immunoblotting ( Figure 2—figure supplement 1a ) and immunohistochemistry ( Figure 2—figure supplement 1b ), thus confirming its mass spectrometric identification.…”

Conservation and divergence of myelin proteome and oligodendrocyte transcriptome profiles between humans and mice

“…For example, we noted that peripheral myelin protein 2 (PMP2, also termed P2 or fatty acid binding protein (FABP8)) was identified in human CNS myelin ( Figure 2b ). PMP2 has long been known as a constituent of myelin in the peripheral nervous system (PNS) synthesized by Schwann cells 20, 21 but based on rodent studies was assumed to be absent from CNS myelin. Yet, PMP2 was readily detected in human CNS myelin by both immunoblotting ( Figure 2- supplement 1a ) and immunohistochemistry ( Figure 2-supplement 1b ), thus confirming its mass spectrometric identification.…”

“…On the other hand, peripheral myelin protein 2 (PMP2, previously termed P2 or FABP8), a membrane-phosphoinositide-binding protein 49 , has long been known as a constituent of peripheral myelin generated by Schwann cells in the PNS 21, 50, 51 and actually considered a marker to discriminate peripheral from central myelin 8, 52, 53 . Notably, the experiments establishing this view involved bovine and rodent but not human samples.…”

“…For example, we noted that peripheral myelin protein 2 (PMP2, also termed P2 or fatty acid binding protein (FABP8)) was identified in human CNS myelin (Figure 2b). PMP2 has long been known as a constituent of myelin in the peripheral nervous system (PNS) synthesized by Schwann cells 20,21 but based on rodent studies was assumed to be absent from CNS myelin.…”

Lipids in Pathophysiology and Development of the Membrane Lipid Therapy: New Bioactive Lipids

“…Peripheral myelin protein P2 is another FABP, and, as one of the most abundant proteins in the human peripheral nervous system (PNS), P2 dysfunction may well lead to myelin degeneration [308]. The structure of this protein has been elucidated, revealing multiple features shared among FABPs, that can drive lipid interactions, including a ligand-binding pocket inside a barrel-like structure [309].…”