Bovine P2 protein: sequence at the NH2-terminal of the protein

Ultrastructural localization of P2 protein in actively myelinating rat Schwann cells

The myelin specific protein, P2, was localized immunocytochemically in electron micrographs of 4-day-old rat peripheral nerve by a preembedding technique. P2 staining was restricted to Schwann cells that had established a one-to-one relationship with an axon. P2 antiserum produced a diffuse staining throughout the entire cytosol of myelinating Schwann cells. In addition, the cytoplasmic side of Schwann cell plasma membranes and the membranes of cytoplasmic organelles that were exposed to cytosol were stained by P2 antiserum. This cytoplasmic localization of P2 protein is similar to that described for soluble or peripheral membrane proteins that are synthesized on free ribosomes. P2 antiserum stained the cytoplasmic side of Schwann cell membranes that formed single or multiple loose myelin spirals around an axon. In the region of the outer mesaxon, P2 antiserum stained the major dense line of compact myelin. These results demonstrate that P2 protein is located on the cytoplasmic side of compact myelin membranes and are consistent with biochemical studies demonstrating P2 to be a peripheral membrane protein.

The passive transfer of severe allergic neuritis in Lewis rats with lymphoid cells preincubated with P2 protein

The passive transfer of both clinical signs and histologic lesions characteristic of allergic neuritis was successfully performed in Lewis rats using pooled spleen and lymph node cells, or T lymphocytes therefrom, if first preincubated in petri dishes with P2 protein for 72 hr. For passive transfer, cells were taken from donors 8-16 days after sensitization with P2 protein or myelin in Freund's complete adjuvant, and administered via the tail vein; clinical signs appeared 12-13 days later. This study supports the importance of cell-mediated immunity in EAN and the antigenic role of the P2 protein.

A general model of the P2 protein of peripheral nervous system myelin based on secondary structure predictions, tertiary folding principles, and experimental observations

The amino acid sequence of the P2 protein of peripheral myelin was analyzed with regard to regions of probable alpha-helix, beta-structure, beta-turn, and unordered conformation by means of several algorithms commonly used to predict secondary structure in proteins. Because of the high beta-sheet content and virtual absence of alpha-helix shown by the circular dichroic spectra of the protein, a bias was introduced into the algorithms to favor the beta-structure over the alpha-helical conformation. In order to define those beta-sheet residues that could lie on the external hydrophilic surface of the protein and those that could lie in its hydrophobic interior, the predicted beta-strands were examined for charged and uncharged amino acids located at alternating positions in the sequence. The sequential beta-strands in the predicted secondary structure were then ordered into beta-sheets and aligned according to generally accepted tertiary folding principles and certain chemical properties peculiar to the P2 protein. The general model of the P2 protein that emerged was a "Greek key" beta-barrel, consisting of eight antiparallel beta-strands with a two-stranded ribbon of antiparallel beta-structure emerging from one end. The model has an uncharged, hydrophobic core and a highly hydrophilic surface. The two Cys residues, which form a disulfide, occur in a loop connecting two adjacent antiparallel strands. Two hydrophilic loops, each containing a cluster of acidic residues and a single Phe, protrude from one end of the molecule. The general model is consistent with many of the properties of the actual protein, including the relatively weak nature of its association with myelin lipids and the positions of amino acid substitutions. Alternative beta-strand orderings yield three specific models having different interstrand connections across the barrel ends.

Structure of bovine P2 basic protein: sequence of a carboxyterminal segment that is a neuritogen in rabbits

The sequence of the carboxyterminal 18 amino acids released by cyanogen bromide digestion of the bovine P2 protein was determined. It has several interesting structural and immunological properties. It contains the only two half-cystines in the molecule that have the capacity to form an intrachain disulfide bond. Using the rabbit as a test animal, this carboxyterminal peptide was capable of producing experimental allergic neuritis. The sequence of this peptide is Val-Val-Glu-Cys-Lys-Met-Lys-Asp-Val-Val-Cys-Thr-Arg-Ile-Tyr-Glu-Lys-Val.

The protein antigens of peripheral nerve myelin

Peripheral nervous system (PNS) tissue contains a variety of proteins, lipids, and carbohydrates that may serve as immunogens in proving immune responses, as antigens participating in immunological reactions, or as both types of agents. Three proteins P0, P1, and P2, account for approximately 70% of PNS myelin proteins. P0 is the major PNS myelin protein and is restricted to the PNS. P1 is similar to, if not identical with, myelin basic protein, the component of central nervous system myelin which induces experimental allergic encephalomyelitis. P2 has neuritogenic properties for inducing experimental allergic neuritis and may be involved in immune-mediated PNS myelin injury in humans. The complete amino acid sequence for P2 has recently been delineated, and its neuritogenic, immunogenic, and antigenic features can now be further characterized.