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Publication Abstract from PubMed

The pi-helix located at the tetramer interface of two-component FMN-dependent reductases contributes to the structural divergence from canonical FMN-bound reductases within the NADPH:FMN reductase family. The pi-helix in the SsuE FMN-dependent reductase of the alkanesulfonate monooxygenase system has been proposed to be generated by the insertion of a Tyr residue in the conserved alpha4-helix. Variants of Tyr118 were generated, and their X-ray crystal structures determined, to evaluate how these alterations affect the structural integrity of the pi-helix. The structure of the Y118A SsuE pi-helix was converted to an alpha-helix, similar to the FMN-bound members of the NADPH:FMN reductase family. Although the pi-helix was altered, the FMN binding region remained unchanged. Conversely, deletion of Tyr118 disrupted the secondary structural properties of the pi-helix, generating a random coil region in the middle of helix 4. Both the Y118A and Delta118 SsuE SsuE variants crystallize as a dimer. The MsuE FMN reductase involved in the desulfonation of methanesulfonates is structurally similar to SsuE, but the pi-helix contains a His insertional residue. Exchanging the pi-helix insertional residue of each enzyme did not result in equivalent kinetic properties. Structure-based sequence analysis further demonstrated the presence of a similar Tyr residue in an FMN-bound reductase in the NADPH:FMN reductase family that is not sufficient to generate a pi-helix. Results from the structural and functional studies of the FMN-dependent reductases suggest that the insertional residue alone is not solely responsible for generating the pi-helix, and additional structural adaptions occur to provide the altered gain of function.

Not as easy as pi: An insertional residue does not explain the pi-helix gain-of-function in two-component FMN reductases.,McFarlane JS, Hagen RA, Chilton AS, Forbes DL, Lamb AL, Ellis HR Protein Sci. 2019 Jan;28(1):123-134. doi: 10.1002/pro.3504. Epub 2018 Nov 15. PMID:30171650^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.