Structural Evidence for Co-Evolution of the Regulation of Contraction and Energy Production in Skeletal Muscle

Skeletal muscle phosphorylase kinase (PhK) is a Ca2+-dependent enzyme complex, (αβγδ)4, with the δ subunit being tightly bound endogenous calmodulin (CaM). The Ca2+-dependent activation of glycogen phosphorylase by PhK couples muscle contraction with glycogen breakdown in the “excitation–contraction...

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Veröffentlicht in:Journal of molecular biology 2008-03, Vol.377 (3), p.623-629
Hauptverfasser: Jeyasingham, Marina D., Artigues, Antonio, Nadeau, Owen W., Carlson, Gerald M.
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Sprache:eng
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Zusammenfassung:Skeletal muscle phosphorylase kinase (PhK) is a Ca2+-dependent enzyme complex, (αβγδ)4, with the δ subunit being tightly bound endogenous calmodulin (CaM). The Ca2+-dependent activation of glycogen phosphorylase by PhK couples muscle contraction with glycogen breakdown in the “excitation–contraction–energy production triad.” Although the Ca2+-dependent protein–protein interactions among the relevant contractile components of muscle are well characterized, such interactions have not been previously examined in the intact PhK complex. Here we show that zero-length cross-linking of the PhK complex produces a covalent dimer of its catalytic γ and CaM subunits. Utilizing mass spectrometry, we determined the residues cross-linked to be in an EF hand of CaM and in a region of the γ subunit sharing high sequence similarity with the Ca2+-sensitive molecular switch of troponin I that is known to bind actin and troponin C, a homolog of CaM. Our findings represent an unusual binding of CaM to a target protein and supply an explanation for the low Ca2+ stoichiometry of PhK that has been reported. They also provide direct structural evidence supporting co-evolution of the coordinate regulation by Ca2+ of contraction and energy production in muscle through the sharing of a common structural motif in troponin I and the catalytic subunit of PhK for their respective interactions with the homologous Ca2+-binding proteins troponin C and CaM.
ISSN:0022-2836
1089-8638
DOI:10.1016/j.jmb.2007.12.072