title: Computational and experimental evidence for the evolution of a (beta alpha)8-barrel protein from an ancestral quarter-barrel stabilised by disulfide bonds.
abstract: The evolution of the prototypical (beta alpha)(8)-barrel protein imidazole glycerol phosphate synthase (HisF) was studied by complementary computational and experimental approaches. The 4-fold symmetry of HisF suggested that its constituting (beta alpha)(2) quarter-barrels have a common evolutionary origin. This conclusion was supported by the computational reconstruction of the HisF sequence of the last common ancestor, which showed that its quarter-barrels were more similar to each other than are those of extant HisF proteins. A comprehensive sequence analysis identified HisF-N1 [corresponding to (beta alpha)(1-2)] as the slowest evolving quarter-barrel. This finding indicated that it is the closest relative of the common (beta alpha)(2) predecessor, which must have been a stable and presumably tetrameric protein. In accordance with this prediction, a recombinantly produced HisF-N1 protein was properly folded and formed a tetramer being stabilised by disulfide bonds. The introduction of a disulfide bond in HisF-C1 [corresponding to (beta alpha)(5-6)] also resulted in the formation of a stable tetramer. The fusion of two identical HisF-N1 quarter-barrels yielded the stable dimeric half-barrel HisF-N1N1. Our findings suggest a two-step evolutionary pathway in which a HisF-N1-like predecessor was duplicated and fused twice to yield HisF. Most likely, the (beta alpha)(2) quarter-barrel and (beta alpha)(4) half-barrel intermediates on this pathway were stabilised by disulfide bonds that became dispensable upon consolidation of the (beta alpha)(8)-barrel.
authors.affiliation: Institute of Biophysics and Physical Biochemistry, University of Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Richter
authors.forename: Manal
authors.initials: M
authors.lastname: Bosnali
authors.forename: Linn
authors.initials: L
authors.lastname: Carstensen
authors.forename: Tobias
authors.initials: T
authors.lastname: Seitz
authors.forename: Helmut
authors.initials: H
authors.lastname: Durchschlag
authors.forename: Samuel
authors.initials: S
authors.lastname: Blanquart
authors.forename: Rainer
authors.initials: R
authors.lastname: Merkl
authors.forename: Reinhard
authors.initials: R
authors.lastname: Sterner
mesh_terms: D000619:Aminohydrolases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D019295:Computational Biology; D004220:Disulfides; D019143:Evolution, Molecular; D008958:Models, Molecular; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020124:Thermotoga maritima / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D004220:Disulfides; D011994:Recombinant Proteins; C087227:imidazole glycerol phosphate synthase; D000619:Aminohydrolases