Abstract
Previous reports indicated that the carboxyl terminal residues, glutamine276-threonine277 in particular, were important for actin affinity of the unacetylated smooth α-tropomyosin. To determine the role of the glutamine and threonine residues in C-terminal region in actin binding, we constructed mutant striated muscle α-tropomyosins (TMs), in which these two residues were individually substituted. These mutant tropomyosins, designated TM18 (HT) and TM19 (QA), were overexpressed in E. coli as an either unacetylated form or Ala-Ser (AS) dipeptide fusion form, and were analyzed F-actin affinity by cosedimentation. Unacetylated TM19 (QA) bound to actin approximately three times stronger than TM18 (HT) and much stronger than ST (HA). AS/TM19 (QA) showed four times stronger in actin affinity than AS/ST (HA) while AS/TM14 (QT) bound to actin stronger to some extent than AS/TM18 (HT). These results suggested that the presence of Gln residue at 276 be primarily attributed to higher actin affinity of smooth α-tropomyosin.
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