Pacak, P. | bioRxiv Science

bioRxiv2024

Force-dependent Reorganization and Mechanostability of the Izumo1:Juno Complex Involved in Human Fertilization

Izumo1:Juno-mediated adhesion between sperm and egg cells is essential for mammalian sexual reproduction. However, conventional biophysical and structural approaches have provided only limited functional insights. Using atomic force microscopy-based single- molecule force spectroscopy and all-atom steered molecular dynamic simulations, we explored the role of mechanical forces in regulating the human Izumo1:Juno complex. Our findings reveal a multi-state catch bond capable of withstanding forces up to 600 pN- mechanostability rarely observed among eukaryotic protein complexes. We further found that this mechanostability was impaired in the infertility-associated mutant, JunoH177Q. Detailed steered molecular dynamics simulations show how force-dependent reorganization of the Izumo1:Juno complex engages new binding conformations to achieve this state of high mechanostability. Overall, this study significantly enhances our understanding of the mechanical underpinnings that regulate human fertilization.

biophysics↗

bioRxiv2023

Tissue Transglutaminase 2 has higher affinity for relaxed than for stretched fibronectin fibers

Tissue transglutaminase 2 (TG2) plays a vital role in stabilizing extracellular matrix (ECM) proteins through enzymatic crosslinking during tissue growth, repair, and inflammation. TG2 also binds non-covalently to fibronectin (FN), an essential component of the ECM, facilitating cell adhesion, migration, proliferation, and survival. However, the interaction between TG2 and fibrillar FN remains poorly understood, as most studies have focused on soluble or surface-adsorbed FN or FN fragments, which differ in their conformations from insoluble FN fibers. Using a well-established in vitro FN-fiber stretch assay, we discovered that the binding of a crosslinking enzyme to ECM fibers is mechano-regulated. TG2 binding to FN is tuned by the mechanical tension of FN fibers, whereby TG2 predominantly co-localizes to low-tension FN fibers, while fiber stretching reduces their affinity for TG2. This mechano-regulated binding relies on the proximity between the N-terminal {beta}-sandwich and C-terminal {beta}-barrels of TG2. Crosslinking mass spectrometry (XL-MS) revealed a novel TG2-FN synergy site within TG2s C-terminal {beta}-barrels that interacts with FN regions outside of the canonical gelatin binding domain, specifically FNI2 and FNIII14-15. Combining XL-MS distance restraints with molecular docking reveals the mechano-regulated binding mechanism between TG2 and modules FNI7-9 by which mechanical forces regulate TG2-FN interactions. This highlights a previously unrecognized role of TG2 as a tension sensor for FN fibers. This novel interaction mechanism has significant implications in physiology and mechanobiology, including how force regulate ECM deposition and maturation, and how TG2 mediates cell-ECM adhesion in health and in various pathophysiological processes. Data are available via ProteomeXchange with identifier PXD043976.

molecular biology↗