Kinetic and spectroscopic analysis of the catalytic role of H79 in the methionine aminopeptidase from Escherichia coli
Graduate School of Biomedical Sciences; Department of Biochemistry and Molecular Pharmacology
Life Sciences | Medicine and Health Sciences
To gain insight into the role of the strictly conserved histidine residue, H79, in the reaction mechanism of the methionyl aminopeptidase from Escherichia coli ( EcMetAP-I), the H79A mutated enzyme was prepared. Co(II)-loaded H79A exhibits an overall >7000-fold decrease in specific activity. The almost complete loss of activity is primarily due to a >6000-fold decrease in k cat. Interestingly, the K m value obtained for Co(II)-loaded H79A was approximately half the value observed for wild-type (WT) EcMetAP-I. Consequently, k cat/ K m values decreased only 3000-fold. On the other hand, the observed specific activity of Mn(II)-loaded H79A EcMetAP-I decreased by approximately 2.6-fold while k cat decreased by approximately 3.5-fold. The observed K m value for Mn(II)-loaded H79A EcMetAP-I was approximately 1.4-fold larger than that observed for WT EcMetAP-I, resulting in a k cat/ K m value that is lower by approximately 3.4-fold. Metal binding, UV-vis, and EPR data indicate that the active site is unperturbed by mutation of H79, as suggested by X-ray crystallographic data. Kinetic isotope data indicate that H79 does not transfer a proton to the newly forming amine since a single proton is transferred in the transition state for both the WT and H79A EcMetAP-I enzymes. Therefore, H79 functions to position the substrate by hydrogen bonding to either the amine group of the peptide linkage or a backbone carbonyl group. Together, these data provide new insight into the catalytic mechanism of EcMetAP-I.
DOI of Published Version
Biochemistry. 2008 Nov 11;47(45):11885-93. Epub 2008 Oct 15. Link to article on publisher's site
Watterson SJ, Mitra S, Swierczek SI, Bennett BT, Holz RC. (2008). Kinetic and spectroscopic analysis of the catalytic role of H79 in the methionine aminopeptidase from Escherichia coli. Morningside Graduate School of Biomedical Sciences Student Publications. https://doi.org/10.1021/bi801499g. Retrieved from https://escholarship.umassmed.edu/gsbs_sp/1404