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Proteolytic digestion patterns of spectrin subunits
Author(s) -
Calvert R.,
Gratzer W.B.
Publication year - 1978
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(78)80572-9
Subject(s) - unit (ring theory) , citation , spectrin , library science , chemistry , computer science , mathematics , cell , biochemistry , mathematics education , cytoskeleton
Spectrin, which is the most abundant protein associated with the erythrocyte membrane, and is evidently involved in maintaining the shape of the cell [I], contains two kinds of subunit, tightly associated with each other [2], in equimolar proportions. These chains have approx. mol. wt 240 000 and 220 000. It has been suggested [3-61 that spectrin may resemble myosin, though the only direct argument for such a view is its reported immunological cross-reaction with the myosin of a smooth muscle [6]. In chemical terms, little is known about the relationship between the two spectrin subunits, and one possibility which must be considered is that one is derived by post-synthetic proteolysis of the other. To establish whether two species are derived from the same gene, originate from genes of common ancestry, or are totally unrelated, presents problems for proteins of such high molecular weight. Conventional peptide maps in particular will be expected to contain too many spots to permit of quantitative comparisons. Papain can be used to accomplish partial degradation of proteins into fragments in a desired size range, in the presence of the dissociating agent, sodium dodecyl sulphate (SDS) [7]. A useful variant of this procedure consists in performing the digestion on an electrophoretic zone cut from an acrylamide gel. This ensures that the starting material is pure, and obviates problems of isolation. The gel slice is then reintroduced as the sample on an acrylamide gel, and electrophoresis is performed as before. Breakdown patterns thus displayed can be compared with great precision. We describe here the results of such a comparison between the two spectrin subunits. We have also compared the patterns of peptides generated by cyanogen bromide cleavage [8]. The results show at once that the sequence of the two chains are t different, but there is clear evidence that they are nevertheless related, and therefore presumably share an ancestral gene. A comparison with myosin and with the cytoplasmic high molecular weight filamentous protein, filamin [9], is also shown.