ISOLATION OF A HIGHLY PURIFIED ENCEPHALITOGENIC PROTEIN FROM BOVINE CORD

Myelin basic protein and demyelinating diseases

Myelin basic protein (MBP) is a major protein component of myelin sheath. Primarily because of its ability to induce experimental allergic encephalomyelitis (EAE) in animals, this protein has been considered to play an important role in the pathogenesis of multiple sclerosis (MS), which is one of the most common demyelinating diseases. Its precise measurement in the cerebrospinal fluid (CSF) has been uncommonly difficult, mainly due to immunoheterogeneity of MBP or MBP-like material. More recently, highly sensitive radioimmunoassay techniques utilizing well-characterized antisera have been developed that facilitated its use in the management of MS. The clinical course of MS is highly variable, and the disease is characterized by periods of remission and relapses. Many studies have demonstrated the release of MBP during relapses and elevated levels of MBP in the CSF can be detected if lumbar puncture is performed within 7 days of the onset of neurologic symptoms suggestive of MS. However, the presence of MBP is not an absolute indicator of MS, as elevated MBP levels are also frequently observed in other demyelinating diseases.

Encephalitogenic protein: structure

Amino acid sequences of encephalitogenic proteins from bovine cord and rabbit brain are reported. The bovine protein contains 45 residues. The rabbit protein is identical except for two isopolar substitutions, a dipeptide and amino acid deletion. Analysis of this protein and a 140-residue myelin basic protein indicates that the smaller protein is a portion of the larger encephalitogen. The larger myelin protein contains at least two encephalitogenic sites.

The isolation and properties of experimental allergic encephalitogenic protein

1. Experimental allergic encephalitogenic (EAE) protein was isolated from ox spinal cord by a modification of the method of Martenson & LeBaron (1966). 2. The protein was examined by acrylamide-gel electrophoresis and its amino acid composition determined. 3. Sedimentation-velocity runs in the ultracentrifuge indicate a molecular weight of about 15100 at pH7.8, and calculation suggests that approx. 137 amino acid residues are present per molecule. 4. Gel-filtration and diffusion studies suggest that the protein is non-globular. 5. Optical-rotatory-dispersion measurements show the protein to have no helical secondary structure even at pH values near to the isoelectric point. In the presence of triphosphoinositide, changes in the optical rotatory dispersion of the protein could be interpreted to mean that it develops a small degree of secondary structure. 6. On treatment with cyanogen bromide the experimental allergic encephalitogenic protein is split into at least two fragments, the larger of which is only about 12% smaller than the parent protein and is antigenically active, and the smaller of which is devoid of antigenic activity.

Experimental allergic encephalomyelitis. Isolation of basic proteins and polypeptides from central nervous tissue

1. Basic protein (mol.wt. 16500) and polypeptides (mol.wt. 3500) were isolated from bovine spinal cord by a procedure involving defatting, acid extraction of the defatted material and repeated chromatography on Sephadex G-50. Similar fractions were isolated from guinea-pig brain. 2. These fractions produced experimental allergic encephalomyelitis in guinea pigs. 3. The polypeptides appeared to be derived from a basic protein of myelin as a result of the action of an acid proteinase during extraction with acid. Similar proteolysis might also occur in the isolation of other biologically active polypeptides from acetone-dried powders of nervous tissue. The activity of the acid proteinase was lowered by defatting with chloroform-methanol. 4. Peptides from tryptic digests of encephalitogenic polypeptides and protein were also encephalitogenic, which suggests that the encephalitogenic determinant may be quite a short sequence of amino acids. 5. These encephalitogenic polypeptides are further examples of antigens of low molecular weight.