PSIBLAST, short for Position-Specific Iterated BLAST, is a computational algorithm widely utilized in bioinformatics and molecular biology to align protein sequences. It is an extension of the Basic Local Alignment Search Tool (BLAST) algorithm, designed to improve the accuracy and sensitivity of sequence alignments.
PSIBLAST incorporates iterative searching methods, meaning that it performs multiple rounds of searching and aligning to gradually expand and refine the sequence database. This iterative process involves using each search result from the previous iteration as a starting point for the subsequent search. By doing so, PSIBLAST enables the identification of more distantly related protein sequences, improving the overall sensitivity of the search.
The "Position-Specific" aspect in PSIBLAST's name refers to its ability to build a position-specific score matrix (PSSM) during each iteration. The PSSM represents the probabilities of finding a particular residue at a given position in the alignment. These matrices are then used to score and align new sequences, enhancing the accuracy of the alignment.
The output of a PSIBLAST analysis typically includes a list of aligned sequences, an E-value indicating the statistical significance of each match, and a PSSM. Researchers can utilize the results to infer evolutionary relationships, identify conserved motifs, and make predictions about protein function.
Due to its high sensitivity and improved accuracy in detecting remote homologs, PSIBLAST is extensively employed in protein sequence analysis, comparative genomics, and protein structure prediction, enabling scientists to better understand the relationship between protein sequences and their biological functions.
