Abstract
Lamin A is a nuclear intermediate filament protein critical for nuclear architecture and mechanics and mutated in a wide range of human diseases. Yet little is known about the molecular architecture of lamins and mechanisms of their assembly. Here we use SILAC cross-linking mass spectrometry to determine interactions within lamin dimers and between dimers in higher-order polymers. We find evidence for a compression mechanism where coiled coils in the lamin A rod can slide onto each other to contract rod length, likely driven by a wide range of electrostatic interactions with the flexible linkers between coiled coils. Similar interactions occur with unstructured regions flanking the rod domain during oligomeric assembly. Mutations linked to human disease block these interactions, suggesting that this spring-like contraction can explain in part the dynamic mechanical stretch and flexibility properties of the lamin polymer and other intermediate filament networks.
Highlights
Lamin A is a nuclear intermediate filament protein critical for nuclear architecture and mechanics and mutated in a wide range of human diseases
Measuring 300 dimers visualised by rotary metal shadowing EM revealed rod lengths ranging respectively from 40.7 to 56.9 nm and from 41.0 to 56.0 for 90% of measurements in Tris and NaPi buffer, with a significant trend towards shorter rods in NaPi buffer: median rod length of 51.1 nm in Tris buffer vs 49.2 nm in NaPi buffer (p-value 4.45 × 10−3) (Fig. 1b, c and Source Data file)
A similar shortening was indicated by analytical ultracentrifugation where an increase in more compact species with S-values higher than the 3.81 S calculated for a dimer with a 51 nm long rod was observed in NaPi buffer (Fig. 1d)
Summary
Lamin A is a nuclear intermediate filament protein critical for nuclear architecture and mechanics and mutated in a wide range of human diseases. We develop a SILAC cross-linking mass spectrometry (CLMS) approach to distinguish intra- and inter-molecular interactions within lamin homomers: between lamin A molecules within dimers and between lamin dimers at tetrameric assembly stages in solution This reveals that three flexible linker regions in the lamin A coiled coil rod can electrostatically drive sliding of adjacent coiled coil segments onto each other to achieve a spring-like contraction in rod length. Our results suggest an alternative mechanism where unstructured head, tail and linker regions allow reversible small-scale deformation of the nucleoskeletal filaments without the drastic α-helix unfolding of the more stable coiled coil segments postulated to govern intermediate filament mechanics[22] This model explains variations in appearance of nucleoskeletal filaments[7] and provides a molecular explanation for many uncharacterised disease mutations in lamin A
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
