Evolution of a Metal-Binding Cluster in the NH2-Terminal Variable Region of Avian Fast Skeletal Muscle Troponin T: Functional Divergence on the Basis of Tolerance to Structural Drifting |
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Authors: | Jian-Ping Jin Rafael A. Samanez |
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Affiliation: | (1) Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106-4970, USA, US |
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Abstract: | This study investigated the evolution of a transition metal ion-binding cluster ([H–X–X–X–H] n ; Tx) in the alternatively spliced NH2-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 NH2-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 NH2-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 NH2-terminal variable region of avian pectoral muscle TnT demonstrates a functional divergence on the basis of tolerance to structural drifting. Received: 2 May 2000 / Accepted: 5 September 2000 |
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Keywords: | : Troponin T isoforms — Pectoral muscle — Turkey — Curassow — Transition metal — Development |
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