5ow3
From Proteopedia
Crystal structure of a C-terminally truncated trimeric ectodomain of the Arabidopsis thaliana gamete fusion protein HAP2
Structural highlights
FunctionHAP2_ARATH Required for male fertility (PubMed:17079265, PubMed:20333238). Plays a role in pollen tube guidance and successful gamete attachment (PubMed:17079265). Essential for the fusion of gametes during double fertilization, where one male gamete fuses with the egg to produce a zygote, and another male gamete fuses with the central cell to produce the endosperm (PubMed:17079265, PubMed:20333238, PubMed:21209845). Mediates the fusion of cell membranes (PubMed:28137780). Not required for pollen tube outgrowth (PubMed:17079265, PubMed:20333238).[1] [2] [3] [4] [5] [6] Publication Abstract from PubMedHAPLESS2 (HAP2) is a broadly conserved, gamete-expressed transmembrane protein that was shown recently to be structurally homologous to viral class II fusion proteins, which initiate fusion with host cells via insertion of fusion loops into the host membrane. However, the functional conformation of the HAP2 fusion loops has remained unknown, as the reported X-ray structure of Chlamydomonas reinhardtii HAP2 lacked this critical region. Here, we report a structure-guided alignment that reveals diversification of the proposed HAP2 fusion loops. Representative crystal structures show that in flowering plants, HAP2 has a single prominent fusion loop projecting an amphipathic helix at its apex, while in trypanosomes, three small nonpolar loops of HAP2 are poised to interact with the target membrane. A detailed structure-function analysis of the Arabidopsis HAP2 amphipathic fusion helix defines key residues that are essential for membrane insertion and for gamete fusion. Our study suggests that HAP2 may have evolved multiple modes of membrane insertion to accommodate the diversity of membrane environments it has encountered during eukaryotic evolution. Evolutionary diversification of the HAP2 membrane insertion motifs to drive gamete fusion across eukaryotes.,Fedry J, Forcina J, Legrand P, Pehau-Arnaudet G, Haouz A, Johnson M, Rey FA, Krey T PLoS Biol. 2018 Aug 13;16(8):e2006357. doi: 10.1371/journal.pbio.2006357., eCollection 2018 Aug. PMID:30102690[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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