Shark Myelin Basic Protein: Amino Acid Sequence, Secondary Structure, and Self‐Association

Abstract

Myelin basic protein (MBP) from the Whaler shark (Carcharhinus obscurus) has been purified from acid extracts of a chloroform/methanol pellet from whole brains. The amino acid sequence of the majority of the protein has been determined and compared with the sequences of other MBPs. The shark protein has only 44% homology with the bovine protein, but, in common with other MBPs, it has basic residues distributed throughout the sequence and no extensive segments that are predicted to have an ordered secondary structure in solution. Shark MBP lacks the triproline sequence previously postulated to form a hairpin bend in the molecule. The region containing the putative consensus sequence for encephalitogenicity in the guinea pig contains several substitutions, thus accounting for the lack of activity of the shark protein. Studies of the secondary structure and self-association have shown that shark MBP possesses solution properties similar to those of the bovine protein, despite the extensive differences in primary structure.

Features and Functions of Oligodendrocytes and Myelin Proteins of Lower Vertebrate Species

“…Myelin basic proteins are common to the myelin of all fish species in general, albeit in most cases sequence homologies to mammalian MBPs are surprisingly low (Saavedra et al 1989;Milne et al 1990;Brösamle and Halpern 2002). Even between trout and zebrafish, only 64% sequence identity is noted (unpublished data).…”

“…Even between trout and zebrafish, only 64% sequence identity is noted (unpublished data). Nevertheless, MBP isolated from the brain of shark in solution adopts a quite similar disordered secondary structure as its mammalian counterpart (Milne et al 1990). Unlike the situation in the mammalian CNS where several splice variants ranging from 14 to 21.5 kDa molecular weight occur (de Ferra et al 1985), in fish only two low-molecular-weight variants are found, namely MBPs 10.6 kDa and MBPl 13.8 kDa, the larger isoform being the dominating component.…”

Myelin basic protein: a multifunctional protein

“…The sequence of MBP is highly conserved from mammals (ten species sequenced) to chicken to clawed frog [23]. MBP is also present in fish, but shark MBP has only 44% homology with mammalian MBP [35,36]. No homologues have been found in fruit fly, nematode, and Ascidian (Ciona intestinalis) genomes [37].…”

Molecular cloning of the myelin basic proteins in the shark, Squalus acanthias, and the ray, Raja erinacia

“…2, arginine,,, to lysine, position 163). (Milne et al, 1990), bovine (Brostoff et al, 1974), and rabbit (Martenson et al, 198 1) sequences were determined by direct amino acid sequencing. Heterodontus (Saavedra et al, 1989), chicken (Zopf et al, 1989), rat (Roach et al, 1983), mouse (Takahashi et al, 1985), and human (Kamholz et al, 1986) sequences were determined by translation of their respective cDNA.…”

“…Modern day cartilaginous fishes, considered to be descended from the earliest vertebrates having myelinated nervous systems, are believed to have originated over 200 million years ago (Cappetta, 1987;Shirai, 1992). Recently, the primary structure of the prominent MBP isoform in two Galeomorph sharks has been reported (Saavedra et al, 1989;Milne et al, 1990). The present study extends primary structure information to two MBP isoforms from species representing the two superorders of elasmobranchs in which sequence information had not previously been ob-tained; the shark, Squalus acanthias (order Squalomorphii), and the ray, Raja erinacia (order Batomorphii).…”