FIGURE 4.

Separation and purification of monomeric and dimeric lipid-free apoA-I^Δ185–243 by gel filtration and resulting MS spectra of intramolecular and intermolecular cross-links identified from each species. ¹⁴N and ¹⁵N apoA-I^Δ185–243 were denatured, mixed 1:1, and reassembled as described under “Experimental Procedures.” Proteins were cross-linked and subjected to gel filtration chromatography. a, mixture of cross-linked monomeric and dimeric apoA-I^Δ185–243. b, purified monomeric (lane 1) and dimeric (lane 2) samples after separation by gel filtration chromatography. The gels were stained with Coomassie Blue. c, mass spectra for the [M+4H]⁴⁺ ion of the cross-linked peptides spanning residues 107–116 and 117–123. Monomeric (blue) and dimeric (green) molecules exhibit a clear intramolecular span in both. d, mass spectra for the [M+4H]⁴⁺ ion of the cross-linked peptides spanning residues 117–123 and 132–140 exhibiting a clear intermolecular span in the dimer and intramolecular span in the monomer.