Because 3D protein structure is generally more well conserved than protein sequence, structural similarity is a good indicator of similar function in two or more proteins.[6][12] Many programs have been developed to screen an unknown protein structure against the Protein Data Bank[16] and report similar structures (for example, FATCAT (Flexible structure AlignmenT by Chaining AFPs (Aligned Fragment Pairs) with Twists),[17] CE (combinatorial extension)[18]) and DeepAlign (protein structure alignment beyond spatial proximity).[19] To deal with the situation that many protein sequences have no solved structures, some function prediction servers such as RaptorX are also developed that can first predict the 3D model of a sequence and then use structure-based method to predict functions based upon the predicted 3D model. In many cases instead of the whole protein structure, the 3D structure of a particular motif representing an active site or binding site can be targeted.[12][20][21][22][23] The Structurally Aligned Local Sites of Activity (SALSA) [21] method, developed by Mary Jo Ondrechen and students, utilizes computed chemical properties of the individual amino acids to identify local biochemically active sites. Databases such as Catalytic Site Atlas[24] have been developed that can be searched using novel protein sequences to predict specific functional sites.