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bioRxiv · 10.1101/324194

Fusion surface structure, function, and dynamics of gamete fusogen HAP2

Feng, J.·Dong, X.·Pinello, J. F.·Zhang, J.·Lu, C.·Iacob, R. E.·Engen, J. R.·Snell, W. J.·Springer, T.
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Abstract

HAP2 is a class II gamete fusogen in many eukaryotic kingdoms. A crystal structure of Chlamydomonas HAP2 shows a trimeric fusion state. Domains D1, D2.1 and D2.2 line the 3-fold axis; D3 and a stem pack against the outer surface. Surprisingly, hydrogen-deuterium exchange shows that surfaces of D1, D2.2 and D3 closest to the 3-fold axis are more dynamic than exposed surfaces. Three fusion helices in the fusion loop of each monomer expose hydrophobic residues at the trimer apex that are splayed from the 3-fold axis, leaving a solvent-filled cavity between the fusion loops in each monomer. At the base of the long fusion loop, Arg185 docks in a carbonyl cage. Comparisons to other structures, dynamics, and the greater effect on Chlamydomonas gamete fusion of mutation of axis-proximal than axis-distal fusion helices suggest that the apical portion of each monomer could tilt toward the 3-fold axis with merger of the fusion helices into a common fusion surface.

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Feng, J., Dong, X., Pinello, J. F., Zhang, J., Lu, C., Iacob, R. E., Engen, J. R., Snell, W. J., Springer, T.. 2018-05-16. Fusion surface structure, function, and dynamics of gamete fusogen HAP2. https://doi.org/10.1101/324194

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