Chazzle, Not a perfect analogy, but picture CCR
Post# of 148150
Not a perfect analogy, but picture CCR5 as a spring stuck in the cell membrane. It winds in and out of the membrane (thus the 7 transmembrane description). The coils of the spring protrude through the cell membrane, forming extra-cellular loops. ECL2 is the primary ligand binding site.
The n-terminus (NH2)is the end of the spring sticking through the membrane and is used by HIV during viral entry.
From Wikipedia: