How are protein domains and motifs identified from sequences?

Protein domains and motifs are identified using: 1) Profile HMM searches - HMMER searches against Pfam database to identify conserved domains with statistical significance. InterProScan integrates multiple databases (Pfam, SMART, CDD, PROSITE). 2) Pattern matching - PROSITE patterns define short motifs using regular expressions. 3) Neural networks - predictors like PSIPRED identify secondary structure, SignalP detects signal peptides. 4) Sequence features - PEST sequences, nuclear localization signals, transmembrane regions have characteristic compositions. Results help predict protein function, subcellular localization, and evolutionary relationships. Domain architecture comparison reveals domain shuffling and protein evolution patterns.