1L9E: Role Of Histidine 269 In Catalysis By Monomeric Sarcosine Oxidase

Citation:
Abstract
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.
PDB ID: 1L9EDownload
MMDB ID: 20454
PDB Deposition Date: 2002/3/22
Updated in MMDB: 2017/11
Experimental Method:
x-ray diffraction
Resolution: 1.85  Å
Source Organism:
Similar Structures:
Biological Unit for 1L9E: monomeric; determined by author
Molecular Components in 1L9E
Label Count Molecule
Protein (1 molecule)
1
Monomeric Sarcosine Oxidase
Molecule annotation
Chemicals (3 molecules)
1
1
2
1
3
1
* Click molecule labels to explore molecular sequence information.

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