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Nestin is a type VI intermediate filament protein and a well-known neural stem cell marker. It is also expressed in high-grade cancer cells, forming copolymerized filaments with vimentin. We previously showed that nestin inhibits the binding of vimentin's tail domain to actin filaments (AFs) by steric hindrance through its large nestin tail domain (NTD), thereby increasing three-dimensional cytoskeleton network mobility, enhancing cell flexibility, and promoting cancer progression. Further, we found that nestin itself stably binds to AFs via the NTD. We therefore hypothesized that the NTD may form a flexible cytoskeletal structure by extending with weak force. In vitro tensile tests using atomic force microscopy were performed to assess the mechanical properties of NTDs. The C-terminus of the NTD bound AFs by bringing the AFM tip modified with the NTD into contact with the AFs on the substrate. NTDs were elongated to approximately 80% of their maximum length at weak forces < 150 pN. Repeated tensile tests revealed that the NTD refolded quickly and behaved like a soft elastic material. We speculate that nestin stably binds AFs, and the NTD extends with weak force, contracting quickly upon load release. Thereby, nestin would absorb mechanical load and maintain cytoskeletal integrity. [ABSTRACT FROM AUTHOR]

Troponin C (TnC) is the Ca2+-sensing subunit of troponin that triggers the contraction of striated muscles. In scallops, the striated muscles consume little ATP energy in sustaining strong contractile forces. The N-terminal domain of TnC works as the Ca2+ sensor in vertebrates, whereas scallop TnC uses the C-terminal domain as the Ca2+ sensor, suggesting that there are differences in the mechanism of the Ca2+-dependent regulation of muscles between invertebrates and vertebrates. Here, we report the crystal structure of Akazara scallop ( Chlamys nipponensis akazara) adductor muscle TnC C-terminal domain (asTnCC) complexed with a short troponin I fragment (asTnIS) and Ca2+. The electron density of a Ca2+ ion is observed in only one of the two EF-hands. The EF-hands of asTnCC can only be in the fully open conformation with the assistance of asTnIS. The number of hydrogen bonds between asTnCC and asTnIS is markedly lower than the number in the vertebrate counterparts. The Ca2+ modulation on the binding between asTnCC and asTnIS is weaker, but structural change of the complex depending on Ca2+ concentration was observed. Together, these findings provide a detailed description of the distinct molecular mechanism of contractile regulation in the scallop adductor muscle from that of vertebrates. [ABSTRACT FROM AUTHOR]

Human EST1A (ever shorter telomeres 1A) is associated with most or all active telomerase in cell extracts and is involved either directly or indirectly in telomere elongation and telomere capping. The C-terminal region of EST1A contains the PIN (PilT N-terminus) domain, a putative nuclease domain. The PIN domain of human EST1A was expressed, purified and crystallized by the sitting-drop vapour-diffusion method. The crystals belonged to space group C2, with unit-cell parameters a = 107.3, b = 51.6, c = 100.5 Å, β = 119.3°, and diffracted X-rays to 1.8 Å resolution. The asymmetric unit contained two molecules of the PIN domain and the solvent content was 57%. [ABSTRACT FROM AUTHOR]