Print E-mail
Volume 42, Number 4, August 2009

Examination of anthrax lethal factor inhibition by siderophores, small hydroxamates, and protamine

Matthew Thomas, Domenic Castignetti
Microbiol Immunol Infect. 2009;42:284-289.

Received: September 2, 2008    Revised: September 18, 2009    Accepted: October 5, 2009   


Corresponding author:

Domenic Castignetti, Department of Biology Loyola University of Chicago, 6525 North Sheridan Road, Chicago, IL 60626, United States. E-mail:


Background and purpose: 

Based on their ability to chelate metals, hydroxamate molecules and siderophores have been successfully used as metalloenzyme inhibitors. As the anthrax thoxin lethal factor (LF) is a zinc (ZN)-metallopeptidase, an investigation of the ability of some small non-siderophore hydroxamate compounds, 5 hydromxamate-containing siderophores, and 1 catecholate siderophore was undertaken to dtermine whether these compounds would inhibit LF. In addition, salmon sperm protamine and ethylenediaminetetraacetic acid were investigated.



A spectrophotometric assay of LF activity, based on its reaction with the substrate (Ac-gly-tyr-Bala-arg-arg-arg-arg-arg-arg-arg-arg-val-leu-arg-p-nitroanilide), was used to assess the degree of inhibition of LF by the putative inhibitors. Procedures were implemented to avoid iron contamination of the test solutions and non-ferrated siderophores and hydroxamates were used as potential inhibitors.



The hydroxamate-containing siderophores displayed limited capacities to inhibit LF, as did the low molecular wight hydroxamate compounds. In contrast, the catecholate siderophore enterobactin and the cationic polyamine salmon sperm protamine demonstrated notable inhibitionof LF at concentrations ranging from approximately 10-200.



 The polyamine salmon sperm protamine which mimics the target site of  proteins cleaved by LF, was the most effective inhibitor of the molecules examined, while the small molecule hydroxamates and the hydroxamate siderophcres were among the poorest. If chelation of the Zn of LF results in LF inhibition by the molecules examined, it is most likely secondary to binding of the putative inhibitors to the active site of LF


Key words:

 Anthrax toxin; Protamines; Siderophores