Thermally induced unfolding of Acanthamoeba myosin II and skeletal muscle myosin: nucleotide effects.
The thermal unfolding of monomeric Acanthamoeba myosin II and rabbit skeletal muscle myosin at pH 7.5 in 0.6 M KCl has been studied by differential scanning calorimetry (DSC) and circular dichroism. A single endotherm (at approximately 40 to 45 degrees C) with a maximum at 41.7 +/- 0.1 degrees C and delta H approximately 1080 +/- kcal/mol is observed for both dephospho- and phospho-myosin II. Skeletal muscle myosin unfolds with less cooperativity over a wider temperature range (approximately 40 to 60 degrees C) with delta H approximately 2500 kcal/mol. The thermal unfolding of either myosin results in a loss of approximately 70% of alpha-helical structures. Saturation of dephospho- or phospho-myosin II with 5'-adenylylimidodiphosphate (AMPPNP) in the presence of Mg2+ produces a second endotherm with a maximum at approximately 49 degrees C. The latter observation is attributed to a stabilization of head regions by nucleotide binding. Indeed, a purified N-terminal myosin II head fragment has been found to unfold with Tmax approximately 41 and approximately 48 degrees C in the absence and presence of AMPPNP, respectively. The stabilization of the head regions is less with ADP+Pi and still smaller with ADP alone. In summary, thermally induced unfolding of myosin II is affected by nucleotide binding to heads, but not by phosphorylation or even removal of a 66-amino-acid tailpiece containing phosphorylation sites. The observed differences in the cooperativity of unfolding myosin II and skeletal muscle myosin relate to differences between rod structures and possibly also head-rod interactions.
Zolkiewski
M
M
Laboratory of Biochemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Redowicz
M J
MJ
Korn
E D
ED
Ginsburg
A
A
D000048:Acanthamoeba / Q000737:chemistry*; D000227:Adenine Nucleotides / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D006358:Hot Temperature; D066298:In Vitro Techniques; D007700:Kinetics; D018482:Muscle, Skeletal / Q000737:chemistry*; D009218:Myosins / Q000737:chemistry* / Q000187:drug effects*; D010710:Phosphates / Q000494:pharmacology; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D011817:Rabbits; D013816:Thermodynamics
D000227:Adenine Nucleotides; D010710:Phosphates; D000255:Adenosine Triphosphate; D009218:Myosins