Characterisation of troponin-T from salmonid fish.
Five major troponin-T isoforms were isolated from the myotomal muscles of Atlantic salmon: three from fast muscle (Tn-T1F, Tn-T2F and Tn-T3F) and two from slow muscle (Tn-T1S and Tn-T2S). In addition to their presence in troponin preparations, these proteins were also recognised to be Tn-T on the basis of immunoreaction with anti-troponin-T antibodies and partial amino acid sequence. The electrophoretic mobility in the presence of SDS of the various Tn-Ts increases in the order: 1S < 1F < 2S < 2F < or = 3F. Compositional analysis shows that the higher M(r) forms (1F and 1S) contain considerably more proline, glutamic acid and alanine than the lower-M(r) forms (2F, 3F and 2S). Every isoform lacks cysteine and phosphoserine is present only in isoforms 2F and 3F. All of the Tn-Ts, with the exception of isoform 1F, are N-terminally blocked. CNBr fragments from same cell type Tn-Ts yield identical sequences over at least fifteen Edman cycles. Two full-length cDNA sequences, presumed to represent 1S and 3F, or isoforms that are highly similar, are reported. As documented for higher vertebrate Tn-Ts, the predicted primary structures display a non-uniform distribution of charged amino acids and greater divergence at each end than in the central section. The most striking difference between the two salmonid proteins is the presence of a N-terminal (proline-, glutamic acid- and alanine-rich) extension of about fifty amino acids in Tn-T1s (278 amino acids) that is missing from the fast muscle Tn-T (223 amino acids). The sequences also differ in that 1S lacks the known phosphorylation site while the fast-type isoform contains serine next to the initiating methionine. Of the two, the slow isoform has accumulated the greater number of substitutions.
Waddleton
D M
DM
Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada.
Jackman
D M
DM
Bieger
T
T
Heeley
D H
DH
D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D003001:Cloning, Molecular; D018076:DNA, Complementary; D007536:Isomerism; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000737:chemistry; D012333:RNA, Messenger / Q000032:analysis; D020317:Salmo salar / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014335:Tropomyosin / Q000378:metabolism; D020107:Troponin T / Q000032:analysis / Q000737:chemistry* / Q000235:genetics*; D014337:Trout
D018076:DNA, Complementary; D012333:RNA, Messenger; D014335:Tropomyosin; D020107:Troponin T