1l9e

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Revision as of 18:16, 20 November 2007

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spinqualitylabelsall models 1l9e, resolution 1.85Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Role of Histidine 269 in Catalysis by Monomeric Sarcosine Oxidase

Overview

Conservative mutation of His269 (to Asn, Ala, or Gln) does, not-significantly affect the expression of monomeric sarcosine oxidase, (MSOX), covalent flavinylation, the physicochemical properties of bound, FAD, or the overall protein structure. Turnover with sarcosine and the, limiting rate of the reductive half-reaction with L-proline at pH 8.0 are, however, nearly 2 orders of magnitude slower than that with with wild-type, MSOX. The crystal structure of the His269Asn complex with, pyrrole-2-carboxylate shows that the pyrrole ring of the inhibitor is, displaced as compared with wild-type MSOX. The His269 mutants all form, charge-transfer complexes with pyrrole-2-carboxylate or methylthioacetate, but the charge-transfer bands are shifted to shorter wavelengths (higher, energy) as compared with wild-type MSOX. Both wild-type MSOX and the, His269Asn mutant bind the zwitterionic form of L-proline. The, E(ox).L-proline complex formed with the His269Asn mutant or wild-type MSOX, contains an ionizable group (pK(a) = 8.0) that is required for conversion, of the zwitterionic L-proline to the reactive anionic form, indicating, that His269 is not the active-site base. We propose that the change in, ligand orientation observed upon mutation of His269 results in a less than, optimal overlap of the highest occupied orbital of the ligand with the, lowest unoccupied orbital of the flavin. The postulated effect on orbital, overlap may account for the increased energy of charge-transfer bands and, the slower rates of electron transfer observed for mutant enzyme complexes, with charge-transfer ligands and substrates, respectively.

About this Structure

1L9E is a Single protein structure of sequence from Bacillus sp. with CL, FAD and IMD as ligands. Active as Sarcosine oxidase, with EC number 1.5.3.1 Full crystallographic information is available from OCA.

Reference

Monomeric sarcosine oxidase: role of histidine 269 in catalysis., Zhao G, Song H, Chen ZW, Mathews FS, Jorns MS, Biochemistry. 2002 Aug 6;41(31):9751-64. PMID:12146941

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