The heavy chain of macrophage myosin is phosphorylated at the tip of the tail
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Abstract:
Myosin purified from rabbit alveolar macrophages has been shown previously to be phosphorylated on the rod portion of the heavy chain and on the 20-kDa light chains (Trotter, J.A. (1982) Biochem Biophys. Res. Commun. 106, 1071-1077). Phosphorylation of the 20-kDa light chains by endogenous kinase activity is associated with a significant enhancement of the actin-activated MgATPase activity (Trotter, J.A., and Adelstein, R.S. (1979) J. Biol. Chem. 254, 8781-8785), whereas the function of heavy-chain phosphorylation is unknown. The isolated heavy chains of myosin purified from freshly harvested cells contain between 0.4 and 1.5 mol of PO4/mol of heavy chain, all esterified to serine residues. Using myosin phosphorylated by incubating living unstimulated macrophages in the presence of 32Pi, two-dimensional thin-layer mapping of tryptic peptides derived from heavy chains yields four phosphopeptides, which are phosphorylated to different extents. Limited trypsin digestion of similar radioactive myosin removes all radioactivity from the heavy chain while reducing its apparent molecular mass by less than 10 kDa. It is concluded that the heavy chain of macrophage myosin is phosphorylated on as many as four serines within 10 kDa of the tip of the tail.
Insights
Rabbit macrophage myosin heavy chains are phosphorylated on serine residues near the tail. This phosphorylation may regulate myosin function, as it occurs within 10 kDa of the tail tip.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Motors
Background:
- Myosin from rabbit alveolar macrophages is phosphorylated on heavy chains and 20-kDa light chains.
- Phosphorylation of 20-kDa light chains enhances MgATPase activity, but heavy chain phosphorylation's function is unknown.
Purpose of the Study:
- To investigate the location and extent of heavy chain phosphorylation in macrophage myosin.
Main Methods:
- Myosin was purified from rabbit alveolar macrophages.
- In vivo phosphorylation using 32Pi in unstimulated macrophages.
- Two-dimensional thin-layer mapping of tryptic phosphopeptides from heavy chains.
- Limited trypsin digestion of phosphorylated myosin.
Main Results:
- Macrophage myosin heavy chains contain 0.4-1.5 mol PO4/mol heavy chain, esterified to serine.
- Four distinct phosphopeptides were identified on the heavy chains.
- Phosphorylation sites are located within 10 kDa of the heavy chain's tail tip.
Conclusions:
- Macrophage myosin heavy chains are phosphorylated on up to four serine residues near the tail.
- This phosphorylation is localized to a specific region of the heavy chain, suggesting a potential regulatory role.