Two biochemically distinct and tissue-specific twinfilin isoforms are generated from the mouse Twf2 gene by alternative promoter usage.
Twf (twinfilin) is an evolutionarily conserved regulator of actin dynamics composed of two ADF-H (actin-depolymerizing factor homology) domains. Twf binds actin monomers and heterodimeric capping protein with high affinity. Previous studies have demonstrated that mammals express two Twf isoforms, Twf1 and Twf2, of which at least Twf1 also regulates cytoskeletal dynamics by capping actin filament barbed-ends. In the present study, we show that alternative promoter usage of the mouse Twf2 gene generates two isoforms, which differ from each other only at their very N-terminal region. Of these isoforms, Twf2a is predominantly expressed in non-muscle tissues, whereas expression of Twf2b is restricted to heart and skeletal muscle. Both proteins bind actin monomers and capping protein, as well as efficiently capping actin filament barbed-ends. However, the N-terminal ADF-H domain of Twf2b interacts with ADP-G-actin with a 5-fold higher affinity than with ATP-G-actin, whereas the corresponding domain of Twf2a binds ADP-G-actin and ATP-G-actin with equal affinities. Taken together, these results show that, like Twf1, mouse Twf2 is a filament barbed-end capping protein, and that two tissue-specific and biochemically distinct isoforms are generated from the Twf2 gene through alternative promoter usage.
Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
Elisa M
EM
Nevalainen
Aneta
A
Skwarek-Maruszewska
Attila
A
Braun
Markus
M
Moser
Pekka
P
Lappalainen
D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001669:Biochemical Phenomena; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009928:Organ Specificity; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D055503:Protein Multimerization; D016415:Sequence Alignment; D013379:Substrate Specificity
D000199:Actins; D007527:Isoenzymes; D008840:Microfilament Proteins; C485190:Twf1 protein, mouse; C485645:TWF2 protein, mouse; C534347:Twf1 protein, rat; C534348:Twf2 protein, rat