Effects of membrane potential and sphingolipid structures on fusion of Semliki Forest virus - PubMed (original) (raw)

Requirements for C-2-C-3 rotation around their bond. (A) The structure of the two stereoisomers of SM,

d

-erythro and

l

-threo, is shown. The positions of hydrogen bond donors and acceptors are indicated by asterisks. The C-2-C-3 axis is indicated by the arrow. The orientation of the hydrogen bond donors and acceptors as well as of the head group of SM viewed along the C-2-C-3 axis is shown in the detached blowup where “a” represents a hydrogen bond acceptor, “d” is a donor, and “a-d” is a hydroxyl that can serve as either an acceptor or donor. Clearly the structures formed by the hydrogen bond donors and acceptors are quite distinct for the two stereoisomers; thus, one (

d

-erythro) form but not the other can, on first principles, specifically interact with SFV E1. Most significantly, the hydroxyl group on C3 points into the page (i.e., down) for

d

-erythro but out of the page (i.e., up)

l

-threo. (B) The Neuman projection (see

www.uic.edu/∼kbruzik/text/chaper6.htm

for a description of Neuman projections), shown on the left, shows the molecule along the C-2-C-3 axis, with C-2 in front projecting three branches (e.g., to H-21, C-1, and N), and C-3 in the back (beneath C-2 in this view) represented by a circle with its three outgoing bonds (to C-4, OH, and H-31). In the side view of the lipids, the straight arrow (shown for C2-ceramide) represents the C-2-C-3 axis and the counterclockwise arrow indicates rotation around the C-2-C-3 bond. As illustrated in the top row, the hydrogens of C-2 (H-21) and C-3 (H-31) can assume an antiperiplanar configuration for sphingosine, C2-ceramide, and lyso-SM. But as illustrated in the bottom row, these hydrogens can exist in a synclinal orientation only for sphingosine. The acyl chain of a ceramide would have to enter the aqueous phase and the polar head group of lyso-SM would have to partition into the hydrocarbon portion of the membrane for the synclinal orientation to occur.