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Tropomyosin-dependent Filament Formation by a Polymerization-defective Mutant Yeast Actin (V266G,L267G)
Journal article   Open access   Peer reviewed

Tropomyosin-dependent Filament Formation by a Polymerization-defective Mutant Yeast Actin (V266G,L267G)

Kuo-Kuang Wen, Bing Kuang and Peter A Rubenstein
The Journal of biological chemistry, Vol.275(51), pp.40594-40600
12/22/2000
DOI: 10.1074/jbc.M007201200
PMID: 10998421
url
https://doi.org/10.1074/jbc.M007201200View
Published (Version of record) Open Access

Abstract

A major function of tropomyosin (TPM) in nonmuscle cells may be stabilization of F-actin by binding longitudinally along the actin filament axis. However, no clear evidence exists in vitro that TPM can significantly affect the critical concentration of actin. We previously made a polymerization-defective mutant actin, GG (V266G, L267G). This actin will not polymerize alone at 25 degrees C but will in the presence of phalloidin or beryllium fluoride. With beryllium fluoride, but not phalloidin, this polymerization rescue is cold-sensitive. We show here that GG-actin polymerizability was restored by cardiac tropomyosin and yeast TPM1 and TPM2 at 25 degrees C with rescue efficiency inversely proportional to TPM length (TPM2 > TPM1 > cardiac tropomyosin), indicating the importance of the ends in polymerization rescue. In the presence of TPM, the apparent critical concentration of actin is 5.5 microm, 10-15-fold higher than that of wild type actin but well below that of the GG-actin alone (>20 microm). Non N-acetylated TPMs did not rescue GG-actin polymerization. The TPMs did not prevent cold-induced depolymerization of GG F-actin. TPM-dependent GG-actin polymerization did not occur at temperatures below 20 degrees C. Polymerization rescue may depend initially on the capture of unstable GG-F-actin oligomers by the TPM, resulting in the strengthening of actin monomer-monomer contacts along the filament axis.

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