AUTOMATED HYDRODYNAMIC MODELING OF A COMPLEX BETWEEN A HUMAN IGE FRAGMENT (FC-EPSILON-3-4) AND THE IGE HIGH-AFFINITY RECEPTOR FC-EPSILON-RIALPHA-CHAIN

The binding of IgE to its high affinity receptor Fc epsilon RI plays a n important role in the allergic response. The interaction between sol uble Fc epsilon RI alpha-chain (sFc epsilon RI alpha) and Fc epsilon 3 -4, a fragment of IgE consisting of the C epsilon 3 and C epsilon 4 he avy chain constant domains, has been studied using analytical ultracen trifugation (Keown et al. this volume). Here we describe the developme nt of a simple automated hydrodynamic modelling technique and its appl ication to this interaction. This procedure utilises sphere models of the two molecules and performs an automated systematic translational s earch of sFc epsilon RI alpha relative to Fc epsilon 3-4. The result o f this is the generation of 40,359 individual models of how the recept or can be placed relative to Fc epsilon 3-4. These are then assessed f or consistency by comparing the sedimentation coefficients generated f or the models to the experimentally determined sedimentation coefficie nts, and are displayed graphically to show allowed and disallowed comp lexes. From this analysis, it is clear that the complex between sFc ep silon RI alpha and Fc epsilon 3-4 is compact, with the most elongated models being excluded. In addition, sFc epsilon RI alpha appears not t o interact with the C-terminal end of Fc epsilon 3-4, and probably bin ds either to the sides or face, observations which are consistent with other experimental data on the Fc epsilon RI alpha/IgE interaction. A utomated hydrodynamic modeling also has the potential to be used for o ther interactions, providing a simple way of looking at a large number of models, and making rigorous studies of interacting components more feasible.