Title

Both Nucleophile and Substrate Bind to the Catalytic Fe(II)-Center in the Type-II Methionyl Aminopeptidase from Pyrococcus furiosus

Document Type

Article

Language

eng

Format of Original

3 p.

Publication Date

3-2005

Publisher

American Chemical Society

Source Publication

Inorganic Chemistry

Source ISSN

0020-1669

Original Item ID

doi: 10.1021/ic0487934

Abstract

Metalloproteases utilize their active site divalent metal ions to generate a nucleophilic water/hydroxide. For methionine aminopeptidases (MetAPs), the exact location of this nucleophile, as well as of the substrate, with respect to the active site metal ion is unknown. In order to address this issue, we have examined the catalytically competent Fe(II)-loaded form of PfMetAP-II ([Fe(PfMetAP-II)]) in the absence and presence of both nitric oxide (NO) and the substrate-analogue inhibitor butaneboronic acid (BuBA) by kinetic and spectroscopic (EPR, UV−vis) methods. NO binds to [Fe(PfMetAP−II)] with a Kd of 200 μM forming an {FeNO}7 complex. UV−vis spectra of the resulting [Fe(PfMetAP−II)]−NO complex indicate that the Fe(II) ion is six coordinate. These data suggest that NO binding occurs without displacing the bound aquo/hydroxo moiety in [Fe(PfMetAP−II)]. On the basis of EPR spectra, the resulting Fe−NO complex is best described as NO- (S = 1) antiferromagnetically coupled to a high-spin Fe(III) ion (S = 5/2). The addition of BuBA to [Fe(PfMetAP-II)]−NO displaces the coordinated water molecule forming a six-coordinate adduct. EPR data also indicate that an interaction between the bound NO- and BuBA occurs forming a complex that mimics an intermediate step between the Michaelis complex and the tetrahedral transition-state.

Comments

Inorganic Chemistry, Vol. 44, No. 5 (March 2005): 1160-1162. DOI.

Brian Bennett was affiliated with Medical College of Wisconsin at the time of publication.

Richard Holz was affiliated with Utah State University at the time of publication.