Proposed technique for classifying and identifying encephalitogens

Myelin basic protein-diverse conformational states of an intrinsically unstructured protein and its roles in myelin assembly and multiple sclerosis

The 18.5 kDa isoform of myelin basic protein (MBP) is a major component of the myelin sheath in the central nervous system of higher vertebrates, and a member of a larger family of proteins with a multiplicity of forms and post-translational modifications (PTMs). The 18.5 kDa protein is the exemplar of the family, being most abundant in adult myelin, and thus the most-studied. It is peripherally membrane-associated, but has generally been investigated in isolated form. MBP is an 'intrinsically unstructured' protein with a high proportion (approximately 75%) of random coil, but postulated to have core elements of beta-sheet and alpha-helix. We review here the properties of the MBP family, especially of the 18.5 kDa isoform, and discuss how its three-dimensional (3D) structure may be resolved by direct techniques available to us, viz., X-ray and electron crystallography, and solution and solid-state NMR spectrometry. In particular, we emphasise that creating an appropriate environment in which the protein can adopt a physiologically relevant fold is crucial to such endeavours. By solving the 3D structure of 18.5 kDa MBP and the effects of PTMs, we will attain a better understanding of myelin architecture, and of the molecular mechanisms that transpire in demyelinating diseases such as multiple sclerosis.

Autoimmune disease antigens

The first step towards understanding the cellular interaction which results in autoimmune disease is to determine what triggers the recognition between a specific autoimmune antigen determinant and the cellular receptor. In this review, we have focused on the antigen inducing experimental allergic encephalitis (EAE) because the antigen has been characterized and a relatively large body of information on its biological activities has been accumulated. Clearly, a specific allergic encephalitis-producing determinant is present and is represented on a relatively small portion of the molecule. The determinant induces a wide variety of biological reactivities, some of which are classed as cellular mediated. An attempt is made to dissect activities such as blast transformation (BT), migration inhibitory factor (MIF), in vivo delayed type hypersensitivity reaction (DTH) and EAE and to relate them to the structural requirements which the determinants possess. The complexities which arise indicate that subpopulations of cells with different receptor activities may respond selectively and that recognition of the receptor is produced by an EAE determinant consisting of three amino acids in a specific linear sequence. Furthermore, under experimental circumstances the EAE activity can be dissociated from the other activities (BT, MIF, DTH), indicating that while these tests are used generally to follow various human autoimmune disease activities, they may represent the reaction of a broad spectrum of cells.

Amino acid sequence of the smaller basic protein from rat brain myelin

1. The complete amino acid sequence of the smaller basic protein from rat brain myelin was determined. This protein differs from myelin basic proteins of other species in having a deletion of a polypeptide of 40 amino acid residues from the centre of the molecule. 2. A detailed comparison is made of the constant and variable regions in a group of myelin basic proteins from six species. 3. An arginine residue in the rat protein was found to be partially methylated. The ratio of methylated to unmethylated arginine at this position differed from that found for the human basic protein. 4. Three tryptic peptides were isolated in more than one form. The differences between the two forms of each peptide are discussed in relation to the electrophoretic heterogeneity of myelin basic proteins, which is known to occur at alkaline pH values. 5. Detailed evidence for the amino acid sequence of the protein has been deposited as Supplementary Publication SUP 50029 at the British Library (Lending Division) (formerly the National Lending Library for Science and Technology), Boston Spa, Yorks. LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1973) 131, 5.

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.