Abstract
The synaptonemal complex (SC) is a supramolecular protein assembly that mediates homologous chromosome synapsis during meiosis. This zipper-like structure assembles in a continuous manner between homologous chromosome axes, enforcing a 100-nm separation along their entire length and providing the necessary three-dimensional framework for cross-over formation. The mammalian SC comprises eight components—synaptonemal complex protein 1–3 (SYCP1–3), synaptonemal complex central element protein 1–3 (SYCE1–3), testis-expressed 12 (TEX12), and six6 opposite strand transcript 1 (SIX6OS1)—arranged in transverse and longitudinal structures. These largely α-helical, coiled-coil proteins undergo heterotypic interactions, coupled with recursive self-assembly of SYCP1, SYCE2–TEX12, and SYCP2–SYCP3, to achieve the vast supramolecular SC structure. Here, we report a novel self-assembly mechanism of the SC central element component SYCE3, identified through multi-angle light scattering and small-angle X-ray scattering (SAXS) experiments. These analyses revealed that SYCE3 adopts a dimeric four-helical bundle structure that acts as the building block for concentration-dependent self-assembly into a series of discrete higher-order oligomers. We observed that this is achieved through staggered lateral interactions between self-assembly surfaces of SYCE3 dimers and through end-on interactions that likely occur through intermolecular domain swapping between dimer folds. These mechanisms are combined to achieve potentially limitless SYCE3 assembly, particularly favoring formation of dodecamers of three laterally associated end-on tetramers. Our findings extend the family of self-assembling proteins within the SC and reveal additional means for structural stabilization of the SC central element.
Highlights
The synaptonemal complex (SC) is a supramolecular protein assembly that mediates homologous chromosome synapsis during meiosis
Whereas the two loops had not been built into the deposited structure, we found that they were visible in electron density maps, so we rebuilt and re-refined the SYCE3 structure against the deposited experimental data (Fig. S1 and Table 1)
We reasoned that this may be due to the 9-amino acid N termini that are present at either end of the molecule but are absent from the crystal structure owing to lack of electron density
Summary
The previously reported SYCE3 crystal structure revealed a compact four-helical bundle formed of two intertwined helixloop-helix chains in an anti-parallel configuration (Fig. 1, b and c) (PDB code 4R3Q [31]). This full-length model fitted closely to experimental SAXS data with a 2 value of 1.46 (Fig. 1e), indicating that scattering data are well-explained by the crystal structure with additional unstructured N termini To confirm these findings, we analyzed a truncated construct of amino acids 12– 88 (with subsequently described point mutation L15N), in which unstructured N termini are removed. SEC-SAXS analysis determined a scattering curve that was closely fitted by the crystal structure (2 ϭ 1.15) (Fig. 3b and Fig. S3g), with a P(r) distribution demonstrating a maximum dimension of 80 Å and an ab initio dummy-atom model that matches the crystal structure (Fig. 3, c and d).
Sign-in/Register to view highlights & summary 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.
