Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
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size corresponding to the hydrophobicity <strong>of</strong> each amino acid drawn from the centre <strong>of</strong><br />
the putative helix. Through calculation <strong>of</strong> the hydrophobic moment <strong>of</strong> an appropriate<br />
residue window (typically 11 – three turns in the alpha-helix) for each position in the<br />
protein sequence, it is possible to draw an “amphipatic pr<strong>of</strong>ile” <strong>of</strong> the protein (Fig.<br />
I.14), and by comparison <strong>with</strong> values obtained from known amphipatic helices it is<br />
possible to predict which protein domains are likely to correspond to amphipatic helices<br />
(Auger, 1993).<br />
Figure I.14 – Amphipatic pr<strong>of</strong>ile <strong>of</strong> gp41 from envelope protein <strong>of</strong> HIV variant bh10 (taken from<br />
Auger, 1993).<br />
2.4. Peptide partitioning to the <strong>membrane</strong><br />
Several approaches have been used to study peptide binding to lipid <strong>membrane</strong>s.<br />
The most important are fluorescence spectroscopy (Santos et al., 2003), circular<br />
dichroism, surface plasmon resonance and isothermal titration calorimetry. The binding<br />
<strong>of</strong> a peptide to the lipid bilayer is not a conventional reaction <strong>with</strong> a defined<br />
stoichiometry. In reality, the process is better described as a water/bilayer partition<br />
problem. Although stable complex formation between <strong>proteins</strong> and specific lipids have<br />
been proved and bound lipid molecules have been observed in the crystal structures <strong>of</strong><br />
some <strong>proteins</strong> (see Section 2.8) (Lee, 2003), this type <strong>of</strong> interaction is not generally<br />
found for most <strong>membrane</strong> <strong>proteins</strong>.<br />
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