This paper discusses the implementation of a three-dimensional (3D) structure motif search of proteins. Each protein structure is represented by a set of secondaiy structure elements (SSEs) which involves α-helix segments and β-strand segments. In describing it, every SSE is further reduced into a two-node graph that consists of the starting amino acid residue, the ending residue and a pseudo-bond between them. The searching algorithm is based on a graph theoretical clique-finding algorithm that has been used for 3D substructure searching in small organic molecules. The program SS3D-P2 was validated using proteins that have well-known 3D motifs, and it correctly found the Greek key motif within an eye lens protein, crystallin that consists of four anti-parallel β strands. The program was also successfully applied to searching for the more complex 3D motif TIM-type β-harrel motif, with a protein structure database from the Protein Data Bank.


E-mail: {hiro,raka}@mis.tutkie.tut.ac.jp