Protein structure alignment is a significant tool to understand evolutionary processes and physicochemical properties of proteins. Important targets of structure alignment are not only monomeric but also oligomeric proteins that sometimes include domain swapping or fusions. Although various protein structural alignment programs have been developed, no method is applicable to any protein pair regardless of the number of chain components and oligomeric states with retaining sequential restrictions: structurally equivalent regions must be aligned in the same order along protein sequences.