258:. The LacY gene is a component of the lac operon that encodes lactose permease, a protein responsible for breaking down lactose into glucose and galactose, alongside transacetylase and beta galactosidase. The absence of lactose permease leads to the inability of lactose to enter the cell for further metabolic processes. Therefore, lactose permease plays a crucial role in the utilization of lactose as a source of energy. LacY, a protein responsible for the transport of lactose across the membrane in Escherichia coli. LacY has a flexible structure consisting of 12 transmembrane helices. The N- and C-terminal domains are symmetric, suggesting they have the same genetic origin. The substrate-binding site is in the N-terminal domain, with residues like Trp151 and Arg144 playing important roles in sugar binding. The C-terminal domain has fewer interactions with TDG, but residues like Lys358 and Asp237 contribute to its binding. Thiol cross-linking underestimates distances, especially on the cytoplasmic side, due to the molecule's fluctuations between inward- and outward-facing conformations.
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The mechanism known as the "six-state" pertains to the six distinct functional conformations or states involved in the cotransport process of the lactose permease cotransporter. In state 1 the LacY protein, adopts an outward-facing conformation. Subsequently, through rapid binding of a hydrogen ion,
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The sugar lies in the hydrophilic core of the protein which is accessible from the periplasm. On binding, a large conformational change takes place which makes the sugar binding site accessible from the cytoplasm. Glutamine residues in positions 241 and 359 guide the sugar towards Phe 27, which
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ions from the outside of the cell binds to a carboxyl group on the enzyme that allows it to undergo a conformational change. This form of lactose permease can bind lactose from outside the cell. The enzyme then everts and lactose is transported inward.
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Abramson J, Smirnova I, Kasho V, Verner G, Iwata S, Kaback HR (November 2003). "The lactose permease of
Escherichia coli: overall structure, the sugar-binding site and the alternating access model for transport".
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and its molecular weight is 45,000 daltons. It exhibits an internal two-fold symmetry, relating the N-terminal six helices onto the C-terminal helices. It is encoded by the
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brings the substrate to Gln 126 where it is firmly fixed. Carefully positioned amino acids help the substrate to overcome the energy barrier of around 20 kJ/mol
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Abramson J, Smirnova I, Kasho V, Verner G, Kaback HR, Iwata S (August 2003). "Structure and mechanism of the lactose permease of
Escherichia coli".
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it transitions to state 2. During state 3, the cotransporter captures a lactose molecule while maintaining an outward-facing conformation.
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308:"Crystal structure of lactose permease in complex with an affinity inactivator yields unique insight into sugar recognition"
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Makar AB, McMartin KE, Palese M, Tephly TR (June 1975). "Formate assay in body fluids: application in methanol poisoning".
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Crystal
Structure of Lactose Permease in Complex with an Affinity Inactivator. PDB
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Proceedings of the
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474:"Uptake dynamics in the Lactose permease (LacY) membrane protein transporter"
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Chaptal V, Kwon S, Sawaya MR, Guan L, Kaback HR, Abramson J (June 2011).
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Kimanius D, Lindahl E, Andersson M (September 2018).
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372:. Hoboken, N.J.: Wiley-Interscience. p. 140.
220:is a membrane protein which is a member of the
19:"lacY" redirects here. Not to be confused with
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224:. Lactose permease can be classified as a
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370:Spectroscopy for the biological sciences
277:was first solved in 2003 by J. Abramson
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240:in the same direction into the cell.
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580:Sun H (2022-02-04). Goudon T (ed.).
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232:towards the cell to transport
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443:10.1016/S0014-5793(03)01087-1
222:major facilitator superfamily
157:Available protein structures:
617:10.1371/journal.pone.0263286
407:10.1016/0006-2944(75)90147-7
245:transmembrane alpha-helices
33:LacY proton/sugar symporter
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498:10.1038/s41598-018-32624-7
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284:The "Six State" Mechanism
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551:10.1126/science.1088196
333:10.1073/pnas.1105687108
275:X-ray crystal structure
243:The protein has twelve
661:Transmembrane proteins
395:Biochemical Medicine
608:2022PLoSO..1763286S
543:2003Sci...301..610A
490:2018NatSR...814324K
324:2011PNAS..108.9361C
656:Transport proteins
478:Scientific Reports
368:Hammes GG (2005).
537:(5633): 610–615.
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16:Membrane protein
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251:gene in the
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265:Mechanism:
142:OPM protein
55:Identifiers
650:Categories
599:2106.06919
293:References
169:structures
267:hydronium
226:symporter
111:PDOC00698
99:IPR022814
63:LacY_symp
636:35120164
586:PLOS ONE
567:36908983
559:12893935
516:30254312
459:22156974
451:14630326
352:21593407
236:such as
186:RCSB PDB
94:InterPro
627:8815909
604:Bibcode
539:Bibcode
531:Science
507:6156506
486:Bibcode
343:3111295
320:Bibcode
238:lactose
106:PROSITE
74:PF01306
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279:et al.
256:operon
201:PDBsum
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87:CL0015
60:Symbol
594:arXiv
563:S2CID
455:S2CID
123:2.A.1
21:lac Y
632:PMID
555:PMID
512:PMID
447:PMID
411:PMID
374:ISBN
348:PMID
273:The
249:lacY
194:PDBj
190:PDBe
173:ECOD
163:Pfam
147:2cfq
118:TCDB
83:clan
81:Pfam
69:Pfam
47:2y5y
25:Lacy
622:PMC
612:doi
547:doi
535:301
502:PMC
494:doi
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338:PMC
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316:108
254:lac
181:PDB
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