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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CONCLUSIONS<br />
VII<br />
CONCLUSIONS<br />
Chapter II ‐ Protein‐Protein and Protein‐Lipid <strong>Interaction</strong>s<br />
<strong>of</strong> M13 Major Coat.<br />
In this chapter an extensive study <strong>of</strong> the protein-protein and protein-lipid<br />
interactions <strong>of</strong> M13 mcp was conducted. The fluorescence self-quenching data obtained<br />
from the study <strong>with</strong> a BODIPY labelled mcp allowed us to conclude that mcp is in fact<br />
monomeric in DOPC bilayers at the conditions used for protein purification and protein<br />
reconstitution. The use <strong>of</strong> two different sites for labelling, resulted in identical results<br />
excluding any possible influence <strong>of</strong> labelling on the oligomerization efficiency <strong>of</strong> mcp.<br />
Nevertheless, as the <strong>studies</strong> <strong>with</strong> lipid bilayers presenting a different hydrophobic<br />
thickness than mcp shows, mcp can aggregate is certain conditions. In this way, it is<br />
possible that at much higher protein concentrations than the one used here (L/P < 50),<br />
some aggregation takes place, although in vivo the presence <strong>of</strong> only one orientation <strong>of</strong><br />
mcp should contribute to keep it monomeric. This could explain the increase in the<br />
levels <strong>of</strong> anionic lipids (cardiolipin and phosphatidylglycerol) in the lipid <strong>membrane</strong> <strong>of</strong><br />
E. coli during the process <strong>of</strong> infection by the bacteriophage M13. Therefore, although<br />
anionic lipids are not required to keep mcp monomeric in normal conditions, at the very<br />
high mcp concentrations found in the sites <strong>of</strong> phage assembly in the lipid <strong>membrane</strong> <strong>of</strong><br />
the host, they might contribute to stabilize the monomeric state <strong>of</strong> the protein, which is<br />
required for correct assembly.<br />
Fluorescence self-quenching <strong>of</strong> BODIPY labelled mcp is more efficient when mcp<br />
is incorporated in bilayers <strong>with</strong> a thinner (positive hydrophobic mismatch) or thicker<br />
(negative hydrophobic mismatch) hydrophobic length, than the hydrophobic domain <strong>of</strong><br />
mcp. This is likely to result from aggregation <strong>of</strong> mcp, and in this case aggregation in<br />
thicker bilayers is significantly more effective than in thinner bilayers. This discrepancy<br />
can be the result <strong>of</strong> the availability <strong>of</strong> alternative methods for protein adaptation in<br />
positive hydrophobic mismatch conditions. In this case, the protein is able to increase<br />
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