Evolutionary Morphing of Tryptophan Synthase: Functional Mechanisms for the Enzymatic Channeling of Indole. Issue 24 (7th December 2018)

• Record Type: Journal Article
• Authors: Fleming, Jennifer R.; Schupfner, Michael; Busch, Florian; Baslé, Arnaud; Ehrmann, Alexander; Sterner, Reinhard; Mayans, Olga
• Is Part Of: Journal of molecular biology. Volume 430:Issue 24(2018)
• Page Start: 5066
• Page End: 5079
• Publication Date: 2018-12-07
• Subjects: substrate channeling -- enzyme -- X-ray crystallography -- enzyme evolution -- enzyme chimera; TrpS tryptophan synthase -- IGP indole-glycerol-phosphate -- GAP glyceraldehyde-3-phosphate -- PLP pyridoxal phosphate -- stTrpS Salmonella typhimurium -- OPS O-phospho-l-serine -- GP α-glycerol-3-phosphate -- TFE trifunctional enzyme -- ssTrpS Sulfolobus solfataricus; Molecular biology -- Periodicals; Biology -- Periodicals; Biochemistry -- Periodicals; Bacteriology -- Periodicals; Molecular Biology -- Periodicals; Biochemistry -- Periodicals; Biologie moléculaire -- Périodiques; Biologie -- Périodiques; Biochimie -- Périodiques; Moleculaire biologie; Biochemistry; Biology; Molecular biology; Periodicals; 572.805
• DOI: 10.1016/j.jmb.2018.10.013
• Languages: English
• ISSNs: 0022-2836

Abstract

Abstract: Tryptophan synthase (TrpS) is a heterotetrameric αββα enzyme that exhibits complex substrate channeling and allosteric mechanisms and is a model system in enzymology. In this work, we characterize proposed early and late evolutionary states of TrpS and show that they have distinct quaternary structures caused by insertions–deletions of sequence segments (indels) in the β-subunit. Remarkably, indole hydrophobic channels that connect α and β active sites have re-emerged in both TrpS types, yet they follow different paths through the β-subunit fold. Also, both TrpS geometries activate the α-subunit through the rearrangement of loops flanking the active site. Our results link evolutionary sequence changes in the enzyme subunits with channeling and allostery in the TrpS enzymes. The findings demonstrate that indels allow protein quaternary architectures to escape "minima" in the evolutionary landscape, thereby overcoming the conservational constraints imposed by existing functional interfaces and being free to morph into new mechanistic enzymes. Graphical Abstract: Highlights: TrpS is a dual-enzyme metabolic channel that evolved from functionally simple isotypes. The crystal structure of the ancestral TrpS variant reveals a novel quaternary structure. The ancestral TrpS also contains a functional substrate channel, but drastically different in its fold path. In TrpS, indels have reshaped subunit interfaces altering complexation and regulatory capabilities. TrpS illustrates the molecular mechanisms of how indels allow the search of new evolutionary space.