Structural and Functional Properties of Tropomyosin Isoforms Tpm4.1 and Tpm2.1

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Andrey S. Logvinov^1,2, Victoria V. Nefedova¹, Daria S. Yampolskaya¹, Sergey Y. Kleymenov^1,3, Dmitrii I. Levitsky¹, and Alexander M. Matyushenko^1,a*

¹Research Centre of Biotechnology, Russian Academy of Sciences, 119071 Moscow, Russia

²Faculty of Biology, Lomonosov Moscow State University, 119991 Moscow, Russia

³Koltzov Institute of Developmental Biology, Russian Academy of Sciences, 119334 Moscow, Russia

^* To whom correspondence should be addressed.

Received March 28, 2023; Revised May 5, 2023; Accepted May 10, 2023

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Tropomyosin (Tpm) is one of the most important partners of actin filament that largely determines its properties. In animal organisms, there are different isoforms of Tpm, which are believed to be involved in the regulation of various cellular functions. However, molecular mechanisms by which various Tpm cytoplasmic regulate of the functioning of actin filaments are still poorly understood. Here, we investigated the properties of Tpm2.1 and Tpm4.1 isoforms and compared them to each other and to more extensively studied Tpm isoforms. Tpm2.1 and Tpm4.1 were very similar in their affinity to F-actin, thermal stability, and resistance to limited proteolysis by trypsin, but differed markedly in the viscosity of their solutions and thermal stability of their complexes with F-actin. The main difference of Tpm2.1 and Tpm4.1 from other Tpm isoforms (e.g., Tpm1.6 and Tpm1.7) was their extremely low thermal stability as measured by the CD and DSC methods. We suggested the possible causes of this instability based on comparing the amino acid sequences of Tpm4.1 and Tpm2.1 with the sequences of Tpm1.6 and Tpm1.7 isoforms, respectively, that have similar exon structure.

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KEY WORDS: tropomyosin isoforms, coiled-coil stability, actin-associated proteins, actin filaments, differential scanning calorimetry

DOI: 10.1134/S0006297923060081

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