Abstract
Twinstar is an ADF/cofilin family protein, which is expressed by the tsr gene in Drosophila melanogaster. Twinstar is one of the main regulators of actin cytoskeleton remodelling and is essential for vital cellular processes like cytokinesis and endocytosis. We have characterized the structure and dynamics of Twinstar by solution NMR spectroscopy, the interaction of Twinstar with rabbit muscle actin by ITC, and biochemical activities of Twinstar through different biochemical assays using fluorescence spectroscopy and ultra-centrifugation. The solution structure of Twinstar shows characteristic ADF-H fold with well-formed G/F-site and F-site for interaction with actin. The structure possesses an extended F-loop, which is rigid at the base, but flexible towards its apical region. Twinstar shares similar dynamics for the G/F-site with C. elegans homologs, UNC-60A and UNC-60B. However, the dynamics of its F-loop are different from its C. elegans homologs. Twinstar shows strong affinity for ADP-G-Actin and ATP-G-Actin with Kds of ~7.6 nM and ~0.4 μM, respectively. It shows mild F-actin depolymerizing activity and stable interaction with F-actin with a Kd of ~5.0 μM. It inhibits the rate of the nucleotide exchange in a dose dependent manner. On the basis of structure, dynamics, and biochemical activity, Twinstar can be taken to execute its biochemical role by facilitating directional growth and maintenance of length of actin filaments. This study characterizes the structure, backbone dynamics, and biochemical activities of Twinstar of Drosophila, which provides an insight into the regulation of actin dynamics in the member of phylum insecta.
