Role of Trp-187 in the annexin V-membrane interaction: a molecular mechanics analysis

The minimized energy mapping of annexin V Trp-187 chi1 x chi2 isomerization supports the existence of two preferential rotameric orientations of the Trp side chain upon annexin V binding to membranes, in agreement with the time-resolved fluorescence results. They correspond to the perpendicular trans (-173 degrees, 73 degrees) and g- (-71 degrees, 83 degrees) rotamers and represent 59 and 28% of the population, respectively. The analysis of their local environment makes it possible to assign the trans rotamer to the long component and the g- rotamer to the short component of the biexponential fluorescence decay. The orientation of these rotamers relative to the protein core suggests a dual role for Trp-187, which might be involved both in the interaction with the phospholipid bilayer and in the formation of the annexin V 2-D array at the surface of the membrane.