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...
Gespeichert in:
Veröffentlicht in: | Journal of molecular biology 2008-03, Vol.377 (3), p.623-629 |
---|---|
Hauptverfasser: | , , , |
Format: | Artikel |
Sprache: | eng |
Schlagworte: | |
Online-Zugang: | Volltext |
Tags: |
Tag hinzufügen
Keine Tags, Fügen Sie den ersten Tag hinzu!
|
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 |