2anp
From Proteopedia
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| , resolution 1.9Å | |||||||
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| Ligands: | , | ||||||
| Activity: | Bacterial leucyl aminopeptidase, with EC number 3.4.11.10 | ||||||
| Related: | 1AMP, 1LOK, 1CP6, 1TXR
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| Resources: | FirstGlance, OCA, PDBsum, RCSB | ||||||
| Coordinates: | save as pdb, mmCIF, xml | ||||||
Functional Glutamate 151 to Histidine mutant of the aminopeptidase from Aeromonas Proteolytica.
Overview
Glutamate151 (E151) has been shown to be catalytically essential for the aminopeptidase from Vibrio proteolyticus (AAP). E151 acts as the general acid/base during the catalytic mechanism of peptide hydrolysis. However, a glutamate residue is not the only residue capable of functioning as a general acid/base during catalysis for dinuclear metallohydrolases. Recent crystallographic characterization of the D-aminopeptidase from Bacillus subtilis (DppA) revealed a histidine residue that resides in an identical position to E151 in AAP. Because the active-site ligands for DppA and AAP are identical, AAP has been used as a model enzyme to understand the mechanistic role of H115 in DppA. Substitution of E151 with histidine resulted in an active AAP enzyme exhibiting a kcat value of 2.0 min(-1), which is over 2000 times slower than r AAP (4380 min(-1)). ITC experiments revealed that ZnII binds 330 and 3 times more weakly to E151H-AAP compared to r-AAP. UV-vis and EPR spectra of CoII-loaded E151H-AAP indicated that the first metal ion resides in a hexacoordinate/pentacoordinate equilibrium environment, whereas the second metal ion is six-coordinate. pH dependence of the kinetic parameters kcat and K(m) for the hydrolysis of L-leucine p-nitroanilide (L-pNA) revealed a change in an ionization constant in the enzyme-substrate complex from 5.3 in r-AAP to 6.4 in E151H-AAP, consistent with E151 in AAP being the active-site general acid/base. Proton inventory studies at pH 8.50 indicate the transfer of one proton in the rate-limiting step of the reaction. Moreover, the X-ray crystal structure of [ZnZn(E151H-AAP)] has been solved to 1.9 A resolution, and alteration of E151 to histidine does not introduce any major conformational changes to the overall protein structure or the dinuclear ZnII active site. Therefore, a histidine residue can function as the general acid/base in hydrolysis reactions of peptides and, through analogy of the role of E151 in AAP, H115 in DppA likely shuttles a proton to the leaving group of the substrate.
About this Structure
2ANP is a Single protein structure of sequence from Vibrio proteolyticus. Full crystallographic information is available from OCA.
Reference
Kinetic, spectroscopic, and X-ray crystallographic characterization of the functional E151H aminopeptidase from Aeromonas proteolytica., Bzymek KP, Moulin A, Swierczek SI, Ringe D, Petsko GA, Bennett B, Holz RC, Biochemistry. 2005 Sep 13;44(36):12030-40. PMID:16142900
Page seeded by OCA on Mon Mar 31 01:55:02 2008
