A thumbwheel mechanism for APOA1 activation of LCAT activity in HDL.
Authors Cooke AL, Morris J, Melchior JT, Street SE, Jerome WG, Huang R, Herr AB, Smith
LE, Segrest JP, Remaley AT, Shah AS, Thompson TB, Davidson WS
Submitted By Submitted Externally on 7/31/2018
Status Published
Journal Journal of lipid research
Year 2018
Date Published 7/1/2018
Volume : Pages 59 : 1244 - 1255
PubMed Reference 29773713
Abstract APOA1 is the most abundant protein in HDL. It modulates interactions that affect
HDL's cardioprotective functions, in part via its activation of the enzyme,
LCAT. On nascent discoidal HDL, APOA1 comprises 10 a-helical repeats arranged in
an anti-parallel stacked-ring structure that encapsulates a lipid bilayer.
Previous chemical cross-linking studies suggested that these APOA1 rings can
adopt at least two different orientations, or registries, with respect to each
other; however, the functional impact of these structural changes is unknown.
Here, we placed cysteine residues at locations predicted to form disulfide bonds
in each orientation and then measured APOA1's ability to adopt the two
registries during HDL particle formation. We found that most APOA1 oriented with
the fifth helix of one molecule across from fifth helix of the other (5/5
helical registry), but a fraction adopted a 5/2 registry. Engineered HDLs that
were locked in 5/5 or 5/2 registries by disulfide bonds equally promoted
cholesterol efflux from macrophages, indicating functional particles. However,
unlike the 5/5 registry or the WT, the 5/2 registry impaired LCAT cholesteryl
esterification activity (P < 0.001), despite LCAT binding equally to all
particles. Chemical cross-linking studies suggest that full LCAT activity
requires a hybrid epitope composed of helices 5-7 on one APOA1 molecule and
helices 3-4 on the other. Thus, APOA1 may use a reciprocating thumbwheel-like
mechanism to activate HDL-remodeling proteins.