In single-particle analysis, a three-dimensional (3-D) structure of a protein is constructed using electron microscopy (EM). The primary process of this 3-D reconstruction is the classification of images according to their Euler angles, the images in each classified group then being averaged to reduce the noise level. In our newly developed strategy of classification, we introduce a topology representing network (TRN) method. It is a modified method of a growing neural gas network (GNG). In this system, a network structure is automatically determined in response to the images input through a growing process. The GNG creates clear averages of the inputs as unit coordinates in multi-dimensional space, which are then utilized for classification¹⁾.

1) T. Ogura, K. Iwasaki & C. Sato, J. Struct. Biol., Vol. 143, 185-200 (2003).