FIGURE 2.

Signaling profile of mutant CXCR4 receptors co-expressed with CXCL12 in yeast. Left panel, canonical receptor topology for CXCR4. The N119S mutation on TM3 is known to produce constitutive active signaling in CXCR4. Cys²⁸ and Cys²⁷⁴, presumed to form a disulfide linkage between N terminus and EC3 loop, is highlighted in white with black background. Right panel illustrates the contrasting functional effect of C28S, C274S, C28S/C274S, C28F/C274F, and C28R/C274E on constitutively active mutant CXCR4 signaling. Lane A illustrates the weak signaling induced by CXCL12 when co-expressed with WT-CXCR4 in yeast. Vector represents the β-galactosidase activity of the engineered yeast in the absence of both receptor and ligand. Each bar represents the means ± S.D. of signaling activity for three independent transformants, and data are representative of at least two independent experiments. Unpaired t test suggests statistical significance with ***, p ≤ 0.0005, and *, p < 0.05 versus no CXCL12.