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

Authors :: Feng J
Dong X
Pinello J
Zhang J
Lu C
Iacob RE
Engen JR
Snell WJ
Springer TA
Source :: ELife [Elife] 2018 Oct 03; Vol. 7. Date of Electronic Publication: 2018 Oct 03.
Publication Year :: 2018
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 loops 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 two fusion loops, 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.<br />Competing Interests: JF, XD, JP, JZ, CL, RI, JE, WS, TS No competing interests declared<br /> (© 2018, Feng et al.)