Hydrogen/deuterium exchange kinetics of apolipophorin-III in lipid-free and phospholipid-bound states. An analysis by Fourier transform infrared spectroscopy.
Attenuated total reflection Fourier transform infrared spectroscopy was used to probe the kinetics of hydrogen/deuterium exchange in Manduca sexta apolipophorin-III (apoLp-III). ApoLp-III is an exchangeable apolipoprotein that is made up of five elongated amphipathic alpha-helices in a helical bundle conformation in the monomeric lipid-free form. Upon interaction with phospholipids, it is postulated to undergo a large conformational change whereby the hydrophobic interior is exposed, facilitating binding to the lipid surfaces. We have used the lipid-free and dimyristoylphosphatidylcholine-bound apoLp-III to study the dynamically variable domains in the two forms. Three populations of amide protons varying in their hydrogen/deuterium exchange rates were found to exist: slow, intermediate, and fast exchanging, which could correspond to completely buried, partially buried, and solvent-exposed domains on the protein in both the states. In lipid-free apoLp-III, 36, 12, and 52% of the total residues contributed to the slow, intermediate, and fast exchanging populations, respectively. In the dimyristoylphosphatidylcholine-bound form, the corresponding distribution was 20, 16, and 64%, representing a 12% increase in the number of exposed residues. The results are discussed in terms of increased solvent accessibility due to gross tertiary structural reorganization.
Raussens
V
V
Laboratoire de Chimie Physique des Macromolécules aux Interfaces, Université Libre de Bruxelles CP 206/2, B-1050 Brussels, Belgium.
Narayanaswami
V
V
Goormaghtigh
E
E
Ryan
R O
RO
Ruysschaert
J M
JM
D000577:Amides / Q000737:chemistry; D000818:Animals; D001053:Apolipoproteins / Q000737:chemistry* / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D018402:Manduca / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011522:Protons; D017550:Spectroscopy, Fourier Transform Infrared
D000577:Amides; D001053:Apolipoproteins; D002352:Carrier Proteins; D011522:Protons; C042470:apolipophorin III; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine