A fluorescence study of single tryptophan-containing mutants of enzyme IImtl of the Escherichia coli phosphoenolpyruvate-dependent mannitol transport system Dijkstra, Durk; Broos, Jaap; Lolkema, Julius; Enequist, H.; Minke, W.; Robillard, G.T. IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below.
Document VersionPublisher's PDF, also known as Version of record Publication date : 1996 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Dijkstra, D., Broos, J., Lolkema, J. S., Enequist, H., Minke, W., & Robillard, G. T. (1996). A fluorescence study of single tryptophan-containing mutants of enzyme IImtl of the Escherichia coli phosphoenolpyruvatedependent mannitol transport system. Biochemistry, 35(21), 6628-6634. DOI: 10.1021/bi952222t Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. ReceiVed September 18, 1995; ReVised Manuscript ReceiVed March 14, 1996 X ABSTRACT: The fluorescence properties of six different single Trp mutants of the mannitol-specific transporter of Escherichia coli were studied in order to derive structural information at different locations in the enzyme. The use of pure detergent and special protein purification protocols was essential for reliable fluorescence spectra, as judged from tyrosine-like fluorescence in a tryptophan-minus mutant . The steady-state fluorescence spectra of EII mtl mutants with single tryptophan residues at positions 30, 42, 109, 117, 320, and 384 provided information concerning the polarity of the environment and the effects of mannitol binding at these positions. Tryptophan positions 42, 109, and 117 with emission maxima ranging from 337 to 340 nm are relatively polar, and position 384 with an emission maximum at 346 nm is highly polar, whereas position 30 is highly apolar with a maximum at 324 nm. The fluorescence characteristics of tryptophan 30 suggest a buried position in a hydrophobic part of the enzyme, which is confirmed by the low Stern-Volmer quenching constant for I -quenching. Positions 109 and 117 show the highest quenching constants, indicating the most exposed positions, whereas positions 320 and 42 are moderately quenched, by I -. The tryptophan residue at position 384 is, even in the absence of externally added quencher, very strongly quenched, possibly by the carboxylate from aspartate 385 or ...