MBP Recombinant Protein

The protein encoded by the classic MBP gene is a major constituent of the myelin sheath of oligodendrocytes and Schwann cells in the nervous system. However, MBP-related transcripts are also present in the bone marrow and the immune system. These mRNAs arise from the long MBP gene (otherwise called "Golli-MBP") that contains 3 additional exons located upstream of the classic MBP exons. Alternative splicing from the Golli and the MBP transcription start sites gives rise to 2 sets of MBP-related transcripts and gene products. The Golli mRNAs contain 3 exons unique to Golli-MBP, spliced in-frame to 1 or more MBP exons. They encode hybrid proteins that have N-terminal Golli aa sequence linked to MBP aa sequence. The second family of transcripts contain only MBP exons and produce the well characterized myelin basic proteins. This complex gene structure is conserved among species suggesting that the MBP transcription unit is an integral part of the Golli transcription unit and that this arrangement is important for the function and/or regulation of these genes. [provided by RefSeq, Jul 2008]

Function: The classic group of MBP isoforms (isoform 4-isoform 14) are with PLP the most abundant protein components of the myelin membrane in the CNS. They have a role in both its formation and stabilization. The smaller isoforms might have an important role in remyelination of denuded axons in multiple sclerosis. The non-classic group of MBP isoforms (isoform 1-isoform 3/Golli-MBPs) may preferentially have a role in the early developing brain long before myelination, maybe as components of transcriptional complexes, and may also be involved in signaling pathways in T-cells and neural cells. Differential splicing events combined with optional post-translational modifications give a wide spectrum of isomers, with each of them potentially having a specialized function. Induces T-cell proliferation. Ref.7

Subunit structure: Homodimer. Isoform 3 exists as a homodimer. Ref.7

Subcellular location: Myelin membrane; Peripheral membrane protein; Cytoplasmic side. Note: Cytoplasmic side of myelin.

Tissue specificity: MBP isoforms are found in both the central and the peripheral nervous system, whereas Golli-MBP isoforms are expressed in fetal thymus, spleen and spinal cord, as well as in cell lines derived from the immune system. Ref.6

Developmental stage: Expression begins abruptly in 14-16 week old fetuses. Even smaller isoforms seem to be produced during embryogenesis; some of these persisting in the adult. Isoform 4 expression is more evident at 16 weeks and its relative proportion declines thereafter.

Post-translational modification: Several charge isomers of MBP; C1 (the most cationic, least modified, and most abundant form), C2, C3, C4, C5, C6, C7, C8-A and C8-B (the least cationic form); are produced as a result of optional PTM, such as phosphorylation, deamidation of glutamine or asparagine, arginine citrullination and methylation. C8-A and C8-B contain each two mass isoforms termed C8-A(H), C8-A(L), C8-B(H) and C8-B(L), (H) standing for higher and (L) for lower molecular weight. C3, C4 and C5 are phosphorylated. The ratio of methylated arginine residues decreases during aging, making the protein more cationic. Ref.23 Ref.24 Ref.25 Ref.26 Ref.27 Ref.28The N-terminal alanine is acetylated (isoform 3, isoform 4, isoform 5 and isoform 6).Arg-241 was found to be 6% monomethylated and 60% symmetrically dimethylated. Ref.22Phosphorylated by TAOK2, VRK2, MAPK11, MAPK12, MAPK14 and MINK1. Ref.23 Ref.24 Ref.25 Ref.26 Ref.27 Ref.28

Involvement in disease: The reduction in the surface charge of citrullinated and/or methylated MBP could result in a weakened attachment to the myelin membrane. This mechanism could be operative in demyelinating diseases such as chronical multiple sclerosis (MS), and fulminating MS (Marburg disease).

Sequence similarities: Belongs to the myelin basic protein family.

Sequence caution: The sequence AAC41944.1 differs from that shown. Reason: Contaminating sequence. The C-terminus contains a Histidine tag.The sequence BAD92223.1 differs from that shown. Reason: Erroneous initiation. Translation N-terminally shortened.The sequence CAH10359.1 differs from that shown. Reason: wrong intron-exon boundaries.