Juxtamembrane Protein Segments That Contribute To Recruitment Of Cholesterol Into Domains

We investigated the properties of several peptides with sequences related to
LWYIK, a segment found in the gp41 protein of HIV and believed to play a role in
sequestering this protein to a cholesterol-rich domain in the membrane. This
segment fulfills the requirements to be classified as a CRAC motif that has been
suggested to predict those proteins that will partition into cholesterol-rich
regions of the membrane. All of the peptides were studied with the terminal amino
and carboxyl groups blocked, i.e., as N-acetyl-peptide-amides. Effects of
cholesterol on the intensity of W emission generally parallel DSC evidence of
sequestration of cholesterol. Modeling studies indicate that all of these
peptides tend to partition with their mass center at the membrane interface at
the level of the hydroxyl of cholesterol. Interaction with cholesterol is dual:
van der Waals interactions between mainly hydrophobic surfaces and electrostatic
stabilization of the cholesterol OH group. Thus, both experiments and modeling
studies indicate that the preference of CRAC motifs for cholesterol-rich domains
might be related to a membrane interfacial preference of the motif, to a capacity
to wrap and block the cholesterol polar OH group by H-bond interactions, and to a
capacity for peptide aromatic side chains to stack with cholesterol. These
results were supported by studies of single mutations in the gp41 protein of
HIV-1, in which L(679) is replaced with I. Despite the similarity of the
properties of these amino acid residues, this single substitution resulted in a
marked attenuation of the ability of JC53-BL HeLa-based HIV-1 indicator cells to
form syncytia.