PT  - JOURNAL ARTICLE
AU  - Feng, Juan
AU  - Dong, Xianchi
AU  - Pinello, Jennifer F.
AU  - Zhang, Jun
AU  - Lu, Chafen
AU  - Iacob, Roxana E.
AU  - Engen, John R
AU  - Snell, Wiliam J.
AU  - Springer, Timothy A.
TI  - Fusion surface structure, function, and dynamics of gamete fusogen HAP2
AID  - 10.1101/324194
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 324194
4099  - http://biorxiv.org/content/early/2018/05/16/324194.short
4100  - http://biorxiv.org/content/early/2018/05/16/324194.full
AB  - 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.