Hemolytic Activity of Truncated Hemolysin A Variants

Proteus species are second only to Escherichia coli as the most common causative agent of urinary tract infections and many harbor several virulence factors that provide inherent uropathogenicity. One of the virulence factors is a hemolysin system comprised of hemolysin A and hemolysin B. Hemolysin B secretes hemolysin A from the periplasmic space where it resides in an inactive state, through the outer membrane into the surrounding extracellular environment. Upon hemolysin B dependent secretion, hemolysin A functions as a hemolysin and disrupts neighboring host cell membranes. In order to describe the mechanism by which hemolysin A is activated for pore formation, we have constructed, expressed, and purified a series of amino terminal truncates and cysteine mutants of hemolysin A capable of complementing the non-secreted full length hemolysin A and restoring hemolytic activity. All of the amino terminal truncates of hemolysin A were shown to activate hemolysis two to three-fold