Fig. 2. Refined parameters useful in distinguishing GPCRs from non-GPCRs. A sliding window recognizer is used to characterize the structure of a protein. A portion of an idealized GPCR is shown. Parameters selected as being particularly useful were (1) average periodicity of the hydrophobicity function; (2) average periodicity of the polarity function; (3) variance in the periodicity of the polarity function; (4) variance in the first derivative of the polarity function; and (5) amino acid usage index. Adapted from (Warr et al., 2001); parameters are described in more detail in Kim et al. (Kim et al., 2000).