Section: New Results

Algorithmic Foundations

Shape Matching by Localized Calculations of Quasi-isometric Subsets

Participants : Frédéric Cazals, Noël Malod-Dognin.

Consider a protein complex involving two partners, the receptor and the ligand. In [16] , we address the problem of comparing their binding patches, i.e. the sets of atoms accounting for their interaction. This problem has been classically addressed by searching quasi-isometric subsets of atoms within the patches, a task equivalent to a maximum clique problem, a NP-hard problem, so that practical binding patches involving up to 300 atoms cannot be handled. We extend previous work in two directions. First, we present a generic encoding of shapes represented as cell complexes. We partition a shape into concentric shells, based on the shelling order of the cells of the complex. The shelling order yields a shelling tree encoding the geometry and the topology of the shape. Second, for the particular case of cell complexes representing protein binding patches, we present three novel shape comparison algorithms. These algorithms combine a Tree Edit Distance calculation (TED) on shelling trees, together with Edit operations respectively favoring a topological or a geometric comparison of the patches. We show in particular that the geometric TED calculation strikes a balance, in terms of accuracy and running time between a purely geometric and topological comparisons, and we briefly comment on the biological findings reported in a companion paper [21] .