Coevolution signals capture the specific packing of secondary structures in protein architecture

Decoding protein structural characteristics and formation is essential to the understanding of its function. Despite the diversity and enormity of protein universe, the dissection of known protein structures has identified regular secondary structure elements （SSEs）, namely, a-helix and β-strand, that constitute the basic structural elements of protein universe （Levitt and Chothia, 1976）. As a remarkable characteristics of the overall topology of a polypeptide, the specific spatial arrangement of these SSEs is a hallmark of the protein tertiary conformation （Murzin et al., 1995）.