@article{1a5b776c449746edbef7e0801a8d1289,
title = "Crystallographic Structures of IlvN·Val/Ile Complexes: Conformational Selectivity for Feedback Inhibition of Aceto Hydroxy Acid Synthases",
abstract = "Conformational factors that predicate selectivity for valine or isoleucine binding to IlvN leading to the regulation of aceto hydroxy acid synthase I (AHAS I) of Escherichia coli have been determined for the first time from high-resolution (1.9-2.43 {\AA}) crystal structures of IlvN·Val and IlvN·Ile complexes. The valine and isoleucine ligand binding pockets are located at the dimer interface. In the IlvN·Ile complex, among residues in the binding pocket, the side chain of Cys43 is 2-fold disordered (1 angles of gauche- and trans). Only one conformation can be observed for the identical residue in the IlvN·Val complexes. In a reversal, the side chain of His53, located at the surface of the protein, exhibits two conformations in the IlvN·Val complex. The concerted conformational switch in the side chains of Cys43 and His53 may play an important role in the regulation of the AHAS I holoenzyme activity. A significant result is the establishment of the subunit composition in the AHAS I holoenzyme by analytical ultracentrifugation. Solution nuclear magnetic resonance and analytical ultracentrifugation experiments have also provided important insights into the hydrodynamic properties of IlvN in the ligand-free and -bound states. The structural and biophysical data unequivocally establish the molecular basis for differential binding of the ligands to IlvN and a rationale for the resistance of IlvM to feedback inhibition by the branched-chain amino acids.",
author = "Akanksha Bansal and Karanth, {N. Megha} and Borries Demeler and Hermann Schindelin and Sarma, {Siddhartha P.}",
note = "Funding Information: The X-ray facilities at the Molecular Biophysics Unit supported by the Science and Engineering Research Board, Department of Science and Technology (DST), India, and access to beamline BM-14 at ESRF supported by funds from the Department of Biotechnology (DBT), India, are gratefully acknowledged. A.B. and S.P.S. thank DBT and DST India for the Mass Spectrometry and NMR facilities at the Indian Institute of Science. A.B. and S.P.S. also thank the Chairperson, Department of Biochemistry, Indian Institute of Science. for use of the analytical ultracentrifuge. The development of UltraScan was supported by National Institutes of Health Grant GM120600 and National Science Foundation (NSF) Grant ACI-1339649 (both to B.D.). Supercomputer calculations were performed on Comet at the San Diego Supercomputing Center (supported by NSF/XSEDE Grant TG-MCB070039N to B.D.) and Lonestar-5 at the Texas Advanced Computing Center (supported by UT Grant TG457201 to B.D.). Funding Information: A.B. is supported by a University Grants Commission Senior Research Fellowship. A.B. is grateful to the DAAD student visitor fellowship program. This work is supported by a DST Grant (EMR/2015/001178) to S.P.S. Notes The authors declare no competing financial interest. Publisher Copyright: Copyright {\textcopyright} 2019 American Chemical Society.",
year = "2019",
month = apr,
day = "16",
doi = "10.1021/acs.biochem.9b00050",
language = "English (US)",
volume = "58",
pages = "1992--2008",
journal = "Biochemistry",
issn = "0006-2960",
publisher = "American Chemical Society",
number = "15",
}