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Reference.org
Threading (protein sequence)
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<p>In <a href="/facts/Molecular_biology/YgqU35ub">molecular biology</a>, protein threading, also known as fold recognition, is a method of <a href="/facts/Protein_structure_prediction/sj6AbLjI">protein modeling</a> which is used to model those <a href="/facts/Protein/Jxmagu3E">proteins</a> which have the same <a href="/facts/Protein_folding/rf3nR2Y1">fold</a> as proteins of known <a href="/facts/Protein_structure/BptnTs9X">structures</a>, but do not have <a href="/facts/Homology_(biology)/muctKlyT">homologous</a> proteins with known structure. It differs from the <a href="/facts/Homology_modeling/rgaHkvJX">homology modeling</a> method of structure prediction as it (protein threading) is used for proteins which do not have their homologous protein structures deposited in the <a href="/facts/Protein_Data_Bank/oUhq4ABD">Protein Data Bank</a> (PDB), whereas homology modeling is used for those proteins which do. Threading works by using statistical knowledge of the relationship between the structures deposited in the PDB and the <a href="/facts/Primary_structure/VaN6MEYh">sequence</a> of the protein which one wishes to model. </p><p>The prediction is made by "threading" (i.e. placing, aligning) each <a href="/facts/Amino_acid/WDxYwBny">amino acid</a> in the target sequence to a position in the template structure, and evaluating how well the target fits the template. After the best-fit template is selected, the structural model of the sequence is built based on the alignment with the chosen template. Protein threading is based on two basic observations: that the number of different folds in nature is fairly small (approximately 1300); and that 90% of the new structures submitted to the PDB in the past three years have similar structural folds to ones already in the PDB. </p>