Competing Roles of Ca and Nonmuscle Myosin IIA on the Dynamics of the Metastasis-Associated Protein S100A4.

The calcium-binding protein S100A4 plays an important role in a wide range of biological processes such as cell motility, invasion, angiogenesis, survival, differentiation, contractility, and tumor metastasis and interacts with a range of partners. To understand the functional roles and interplay of S100A4 binding partners such as Ca and nonmuscle myosin IIA (NMIIA), we used molecular dynamics simulations to investigate apo S100A4 and four holo S100A4 structures: S100A4 bound to Ca, S100A4 bound to NMIIA, S100A4 bound to Ca and NMIIA, and a mutated S100A4 bound to Ca and NMIIA. Our results show that two competing factors, namely, Ca-induced activation and NMIIA-induced inhibition, modulate the dynamics of S100A4 in a competitive manner. Moreover, Ca binding results in enhanced dynamics, regulating the interactions of S100A4 with NMIIA, while NMIIA induces asymmetric dynamics between the chains of S100A4. The results also show that in the absence of Ca the S100A4-NMIIA interaction is weak compared to that of between S100A4 bound to Ca and NMIIA, which may offer a quick response to dropping calcium levels. In addition, certain mutations are shown to play a marked role on the dynamics of S100A4. The results described here contribute to understanding the interactions of S100A4 with NMIIA and the functional roles of Ca, NMIIA, and certain mutations on the dynamics of S100A4. The results of this study could be interesting for the development of inhibitors that exploit the shift of balance between the competing roles of Ca and NMIIA.