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

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• 作者：Marina D. Jeyasingham ; Antonio Artigues ; Owen W. Nadeau ; Gerald M. Carlson
• 关键词：calmodulin ; co-evolution ; energy production ; phosphorylase kinase ; troponin I
• 刊名：Journal of Molecular Biology
• 出版年：2008
• 出版时间：28 March 2008
• 年：2008
• 卷：377
• 期：3
• 页码：623-629
• 全文大小：386 K

文摘

Skeletal muscle phosphorylase kinase (PhK) is a Ca²⁺-dependent enzyme complex, (βγδ)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.