Interaction of muscle and non-muscle tropomyosins with deoxyribonuclease I.
The sulfhydryl-selective fluorescent reagent acrylodan (6-acryloyl-2-dimethylaminonaphthalene) was used to label tropomyosins from rabbit cardiac muscle and from equine platelets. Addition of bovine pancreatic deoxyribonuclease I to solutions of acrylodan-modified tropomyosins significantly altered the emission properties of the samples. Muscle and non-muscle tropomyosin fluorescence were affected in qualitatively similar manners; emission maxima were red-shifted by about 8 nm to 522-525 nm and maximal intensities were reduced by approximately 15%. Addition of KI to each of the fluorescent samples caused a greater degree of fluorescence quenching in the presence of DNase I than in its absence. The slopes of Stern-Volmer plots were 15-25% steeper in the presence of DNase I. Fluorescence polarization values for acrylodan-labelled tropomyosin samples were 25-35% lower in the presence of DNase I. Each of these effects could be saturated by addition of about a two-fold molar excess of DNase I to tropomyosin. Together they suggest that interaction with DNase I causes localized unfolding of tropomyosin, thereby allowing the fluorescent label to become more exposed to the solvent and less restricted in its local motions. Circular dichroism measurements support this idea. Addition of DNase I to solutions of either labelled or unlabelled tropomyosin results in a net 14-18% loss in ellipticity near 220 nm, indicative of unfolding of alpha-helix.
Clark
I D
ID
Department of Chemistry, University of British Columbia, Vancouver, Canada.
Burtnick
L D
LD
D000818:Animals; D002942:Circular Dichroism; D003850:Deoxyribonuclease I; D005453:Fluorescence; D006736:Horses; D009132:Muscles / Q000032:analysis; D011487:Protein Conformation; D014335:Tropomyosin
D014335:Tropomyosin; D003850:Deoxyribonuclease I