Phyre and Phyre2 (Protein Homology/AnalogY Recognition Engine; pronounced as 'fire') are free web-based services for protein structure prediction. Phyre is among the most popular methods for protein structure prediction having been cited over 1500 times. Like other remote homology recognition techniques (see protein threading), it is able to regularly generate reliable protein models when other widely used methods such as PSI-BLAST cannot. Phyre2 has been designed to ensure a user-friendly interface for users inexpert in protein structure prediction methods. Its development is funded by the Biotechnology and Biological Sciences Research Council. Description The Phyre and Phyre2 servers predict the three-dimensional structure of a protein sequence using the principles and techniques of homology modeling. Because the structure of a protein is more conserved in evolution than its amino acid sequence, a protein sequence of interest (the target) can be modeled with reasonable accuracy on a very distantly related sequence of known structure (the template), provided that the relationship between target and template can be discerned through sequence alignment. Currently the most powerful and accurate methods for detecting and aligning remotely related sequences rely on profiles or hidden Markov models (HMMs). These profiles/HMMs capture the mutational propensity of each position in an amino acid sequence based on observed mutations in related sequences and can be thought of as an 'evolutionary fingerprint' of a particular protein. Typically, the amino acid sequences of a representative set of all known three-dimensional protein structures is compiled, and these sequences are processed by scanning against a large protein sequence database. The result is a database of profiles or HMMs, one for each known 3D structure. A user sequence of interest is similarly processed to form a profile/HMM. This user profile is then scanned against the database of profiles using profile-profile or HMM-HMM alignment techniques. These alignments can also take into account patterns of predicted or known secondary structure elements and can be scored using various statistical models. See protein structure prediction for more information. The first Phyre server was released in June 2005 and uses a profile-profile alignment algorithm based on each protein's position-specific scoring matrix. The Phyre2 server was publicly released February 2011 as a replacement for the original Phyre server and provides extra functionality over Phyre, a more advanced interface, fully updated fold library and uses the HHpred / HHsearch package for homology detection among other improvements. Standard usage After pasting a protein amino acid