Sequential structure alignment program: Difference between revisions

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{{contextTechnical|date=NovemberOctober 20092021}}

The '''sequential structure alignment program (SSAP)''' in [[chemistry]], [[physics]], and [[biology]] is a method that uses double [[dynamic programming]] to produce a structural alignment based on atom-to-atom [[Vector (geometric)|vectors]] in structure space.<ref>{{Cite journal

| last1 = Taylor | first1 = W. R.

| last2 = Orengo | first2 = C. A.

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| pmid = 2769748

| doi=10.1016/0022-2836(89)90084-3

}}</ref><ref>{{Cite journalbook

| last1 = Orengo | first1 = C. A.

| last2 = Taylor | first2 = W. R.

| titlechapter = SSAP: Sequential structure alignment program for protein structure comparison

| journaltitle = Computer Methods infor Macromolecular Sequence enzymologyAnalysis

| series = Methods in Enzymology

| volume = 266

| pages = 617–635

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| pmid = 8743709

| doi=10.1016/s0076-6879(96)66038-8

| isbn = 9780121821678

}}</ref> Instead of the alpha carbons typically used in structural alignment, SSAP constructs its vectors from the [[beta carbon]]s for all residues except glycine, a method which thus takes into account the [[wikt:rotamer|rotameric state]] of each residue as well as its ___location along the backbone. SSAP works by first constructing a series of inter-residue distance vectors between each residue and its nearest non-contiguous neighbors on each protein. A series of matrices are then constructed containing the vector differences between neighbors for each pair of residues for which vectors were constructed. Dynamic programming applied to each resulting matrix determines a series of optimal local alignments which are then summed into a "summary" matrix to which dynamic programming is applied again to determine the overall structural alignment.

SSAP originally produced only pairwise alignments but has since been extended to multiple alignments as well.<ref name="taylor">{{Cite journal

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| pmid = 7849601

| pmc =2142613

}}</ref> It has been applied in an all-to-all fashion to produce a hierarchical fold classification scheme known as [[CATH]] (Class, Architecture, Topology, Homology),.<ref name="Orengo1997">{{cite journal |authorauthor1=Orengo CA, |author2=Michie AD, |author3=Jones S, |author4=Jones DT, |author5=Swindells MB, |author6=Thornton JM |title=CATH—a hierarchic classification of protein ___domain structures |journal=Structure |volume=5 |issue=8 |pages=1093–1108 |year=1997 |pmid=9309224 |doi=10.1016/S0969-2126(97)00260-8|doi-access=free }}</ref> which has been used to construct the [https://web.archive.org/web/20070517161248/http://www.cathdb.info/latest/index.html CATH Protein Structure Classification] database.

Generally, SSAP scores above 80 are associated with highly similar structures. Scores between 70 and 80 indicate a similar fold with minor variations. Structures yielding a score between 60 and 70 do not generally contain the same fold, but usually belong to the same protein class with common structural motifs.<ref name="porwal">{{Cite journal

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| pmid = 17450548

| pmc =

| s2cid = 5710322

}}</ref>