Evolution of a metal-binding cluster in the NH(2)-terminal variable region of avian fast skeletal muscle troponin T: functional divergence on the basis of tolerance to structural drifting.
This study investigated the evolution of a transition metal ion-binding cluster ([H--X--X--X--H](n); Tx) in the alternatively spliced NH(2)-terminal variable region of avian pectoral muscle troponin T (TnT). Encoded by avian fast skeletal muscle TnT-specific P exons, Tx-like structures were expressed in the breast muscle TnT's of almost all birds examined. Their presence results in the developmentally up-regulated high molecular weight pectoral muscle TnT. Sequence analysis and metal affinity chromatography revealed that in Galliformes and Craciformes, the Tx structure evolved into multiple H--X--X--X--H pairs with a high-affinity metal-binding capacity. Turkey, chicken, quail, and curassow breast muscle TnT's contain nine, seven, four, and three consecutive or closely located metal-binding sites, respectively, in the NH(2)-terminal region. The metal-binding affinity of the Tx element increased as the number of His pairs increased due to the duplication of P exons and the conversion of other exon sequences. The data show two related components of avian pectoral muscle TnT evolution: a larger, more acidic NH(2)-terminal segment and a cluster of transition metal-binding sites, both of which may have functional significance for their selection value. The evolution of the Tx segment in the NH(2)-terminal variable region of avian pectoral muscle TnT demonstrates a functional divergence on the basis of tolerance to structural drifting.
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4970, USA. jxj12@po.cwru.edu
J P
JP
Jin
R A
RA
Samanez
D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001717:Birds / Q000235:genetics*; D015153:Blotting, Western; D002846:Chromatography, Affinity; D019143:Evolution, Molecular; D008116:Lizards / Q000235:genetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D018482:Muscle, Skeletal / Q000737:chemistry; D010369:Pectoralis Muscles / Q000737:chemistry*; D010802:Phylogeny; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D020449:Repetitive Sequences, Amino Acid; D016415:Sequence Alignment; D020107:Troponin T / Q000737:chemistry* / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D014426:Turtles / Q000235:genetics; D015032:Zinc / Q000378:metabolism*
D000906:Antibodies; D020033:Protein Isoforms; D020107:Troponin T; D015032:Zinc