Species-Specific Functional Regions of the Green Alga Gamete Fusion Protein HAP2 Revealed by Structural Studies

？ Unprecedented organization of amphipathic α helices in the algal HAP2 fusion loops ？ An inserted EGF-like motif suggests a potential algal-specific fusion control site ？ An adjacent mucin-like region potentially modulates algal-specific interactions ？ Inter-chain stem/domain II interactions stabilize the post-fusion hairpin conformatio