3i3e

E. COLI (lacZ) BETA-GALACTOSIDASE (M542A)

spinqualitylabelsall models 3i3e, resolution 2.10Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Structural highlights 3i3e is a 4 chain structure with sequence from Escherichia coli K-12. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Method: X-ray diffraction, Resolution 2.1Å Ligands: DMS, MG, NA Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Function BGAL_ECOLI Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMed The Met-542 residue of beta-galactosidase is important for the enzyme's activity because it acts as a guide for the movement of the benzyl side chain of Phe-601 between two stable positions. This movement occurs in concert with an important conformational change (open vs. closed) of an active site loop (residues 794-803). Phe-601 and Arg-599, which interact with each other via the pi electrons of Phe-601 and the guanidium cation of Arg-599, move out of their normal positions and become disordered when Met-542 is replaced by an Ala residue because of the loss of the guide. Since the backbone carbonyl of Phe-601 is a ligand for Na(+), the Na(+) also moves out of its normal position and becomes disordered; the Na(+) binds about 120 times more poorly. In turn, two other Na(+) ligands, Asn-604 and Asp-201, become disordered. A substrate analog (IPTG) restored Arg-599, Phe-601, and Na(+) to their normal open-loop positions, whereas a transition state analog d-galactonolactone) restored them to their normal closed-loop positions. These compounds also restored order to Phe-601, Asn-604, Asp-201, and Na(+). Binding energy was, however, necessary to restore structure and order. The K(s) values of oNPG and pNPG and the competitive K(i) values of substrate analogs were 90-250 times higher than with native enzyme, whereas the competitive K(i) values of transition state analogs were ~3.5-10 times higher. Because of this, the E*S energy level is raised more than the E*transition state energy level and less activation energy is needed for galactosylation. The galactosylation rates (k) of M542A-beta-galactosidase therefore increase. However, the rate of degalactosylation (k) decreased because the E*transition state complex is less stable. Role of Met-542 as a guide for the conformational changes of Phe-601 that occur during the reaction of β-galactosidase (Escherichia coli).,Dugdale ML, Dymianiw DL, Minhas BK, D'Angelo I, Huber RE Biochem Cell Biol. 2010 Oct;88(5):861-9. PMID:20921997 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See Also Galactosidase 3D structures

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