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Functional effects of mutations in the tropomyosin‐binding sites of tropomodulin1 and tropomodulin3
Author(s) -
Lewis Raymond A.,
Yamashiro Sawako,
Gokhin David S.,
Fowler Velia M.
Publication year - 2014
Publication title -
cytoskeleton
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.95
H-Index - 86
eISSN - 1949-3592
pISSN - 1949-3584
DOI - 10.1002/cm.21179
Subject(s) - biology , tropomyosin , biophysics , actin , microbiology and biotechnology
Tropomodulins (Tmods) interact with tropomyosins (TMs) via two TM‐binding sites and cap the pointed ends of TM‐coated actin filaments. To study the functional interplay between TM binding and TM‐actin filament capping by Tmods, we introduced disabling mutations into the first, second, or both TM‐binding sites of full‐length Tmod1 (Tmod1‐L27G, Tmod1‐I131D, and Tmod1‐L27G/I131D, respectively) and full‐length Tmod3 (Tmod3‐L29G, Tmod3‐L134D, and Tmod3‐L29G/L134D, respectively). Tmod1 and Tmod3 showed somewhat different TM‐binding site utilization, but nearly all TM binding was abolished in Tmod1‐L27G/I131D and Tmod3‐L29G/L134D. Disruption of Tmod‐TM binding had a modest effect on Tmod1's ability and no effect on Tmod3's ability to stabilize TM‐actin pointed ends against latrunculin A‐induced depolymerization. However, disruption of Tmod‐TM binding did significantly impair the ability of Tmod3 to reduce elongation rates at pointed ends with α/βTM, albeit less so with TM5NM1, and not at all with TM5b. For Tmod1, disruption of Tmod‐TM binding only slightly impaired its ability to reduce elongation rates with α/βTM and TM5NM1, but not at all with TM5b. Thus, Tmod‐TM binding has a greater influence on Tmods' ability to inhibit subunit association as compared to dissociation from TM‐actin pointed ends, particularly for α/βTM, with Tmod3's activity being more dependent on TM binding than Tmod1's activity. Nevertheless, disruption of Tmod1‐TM binding precluded Tmod1 targeting to thin filament pointed ends in cardiac myocytes, suggesting that the functional effects of Tmod‐TM binding on TM‐coated actin filament capping can be significantly modulated by the in vivo conformation of the pointed end or other factors in the intracellular environment. © 2014 Wiley Periodicals, Inc.