Open AccessCalponin Inhibits Actin‐Activated MgATPase of Myosin Subfragment 1 (S1) Without Displacing S1 from Its Binding Site on Actin
Author(s) -
Kołakowski Janusz,
Karkucińska Agnieszka,
Dąbrowska Renata
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00624.x
Subject(s) - calponin , actin , myosin , microbiology and biotechnology , chemistry , biophysics , atpase , microfilament , biochemistry , biology , cytoskeleton , enzyme , cell
Calponin is a smooth‐muscle thin‐filament protein implicated in the regulation of contraction. Its binding to actin is a prerequisite for inhibition of actin‐activated myosin MgATPase. Investigating the molecular mechanism of this inhibition, it was found that titration of acto‐myosin subfragment 1 with calponin in the presence of either ADP or ATP does not displace weakly or strongly bound myosin subfragment 1 (S1) from actin. S1. ADP, however, is able to release about two‐thirds of the calponin from saturated (equimolar) complexes of actin‐calponin. The remaining calponin is sufficient for almost full inhibition of acto‐Sl MgATPase activity. Bundling of actin filaments by calponin takes place at a higher ratio calponin/actin (above 1:3) and, therefore, is not responsible for inhibition of the ATPase. Bundle formation is inhibited by S1 ADP. These results suggest the existence of two calponin‐binding sites on actin; one, that is insensitive to S1, which is responsible for inhibition of the ATPase, the other, from which calponin is readily displaced by S1.