Changes

All the biological organisms on Earth consist of molecules. Among others,&nbsp;protein is&nbsp;the most important unit of life. Proteins consist of amino acids<br />

and amino acids consist of atoms. Proteins are a versatile and diverse structures; small proteins contain several hundreds&nbsp;of atoms while&nbsp;large proteins&nbsp;contain&nbsp;millions of&nbsp;atoms. Not only that, proteins have an extremely diverse repetoire of 3D structures. For example, some proteins are extremely long fibers while some others are almost perfect spheres. Depending the overall shapes, the proteins function completely differently.&nbsp;Therefore, representing protein shapes is an important primary&nbsp;research problem in biology. Classifying proteins or mapping the protein universe has been a core research area in structural biology in&nbsp;the last four decades. Proteins are usually classified by their secondary structure contents&nbsp;such as alpha-helix,&nbsp;beta-sheets, and coils. This secondary structure based classification is useful for studying the&nbsp;evolution of proteins. For classifying proteins and mapping their structure-function relationships,&nbsp;researchers use structure representation descriptors. As proteins are dynamic and versatile&nbsp;molecules, there can be different ways of representing the&nbsp;basic 3D architecture. Until now, there are many&nbsp;physical&nbsp;representation models&nbsp;for protein structures. One of the most popular and convenient models is a hard-sphere model with a fixed<br />