title: Serine protease PrtA from Streptococcus pneumoniae plays a role in the killing of S. pneumoniae by apolactoferrin.
abstract: It is known that apolactoferrin, the iron-free form of human lactoferrin, can kill many species of bacteria, including Streptococcus pneumoniae. Lactoferricin, an N-terminal peptide of apolactoferrin, and fragments of it are even more bactericidal than apolactoferrin. In this study we found that apolactoferrin must be cleaved by a serine protease in order for it to kill pneumococci. The serine protease inhibitors were able to block killing by apolactoferrin but did not block killing by a lactoferrin-derived peptide. Thus, the killing of pneumococci by apolactoferrin appears to require a protease to release a lactoferricin-like peptide(s). Incubation of apolactoferrin with growing pneumococci resulted in a 12-kDa reduction in its molecular mass, of which about 7 to 8 kDa of the reduction was protease dependent. Capsular type 2 and 19F strains with mutations in the gene encoding the major cell wall-associated serine protease, prtA, lost much of their ability to degrade apolactoferrin and were relatively resistant to killing by apolactoferrin (P < 0.001). Recombinant PrtA was also able to cleave apolactoferrin, reducing its mass by about 8 kDa, and greatly enhance the killing activity of the solution containing the apolactoferrin and its cleavage products. Mass spectroscopy revealed that PrtA makes a major cut between amino acids 78 and 79 of human lactoferrin, removing the N-terminal end of the molecule (about 8.6 kDa). The simplest interpretation of these data is that the mechanism by which apolactoferrin kills Streptococcus pneumoniae requires the release of a lactoferricin-like peptide(s) and that it is this peptide(s), and not the intact apolactoferrin, which kills pneumococci.
authors.affiliation: Department of Microbiology, Division of Epidemiology, University of Alabama at Birmingham, 845 19th Street South, Birmingham, AL 35294-2170, USA.
authors.forename: Shaper
authors.initials: S
authors.lastname: Mirza
authors.forename: Landon
authors.initials: L
authors.lastname: Wilson
authors.forename: William H
authors.initials: WH
authors.lastname: Benjamin
authors.forename: Jan
authors.initials: J
authors.lastname: Novak
authors.forename: Stephen
authors.initials: S
authors.lastname: Barnes
authors.forename: Susan K
authors.initials: SK
authors.lastname: Hollingshead
authors.forename: David E
authors.initials: DE
authors.lastname: Briles
mesh_terms: D001059:Apoproteins / Q000502:physiology*; D015153:Blotting, Western; D003001:Cloning, Molecular; D054884:Host-Pathogen Interactions; D006801:Humans; D007781:Lactoferrin / Q000502:physiology*; D011008:Pneumococcal Infections / Q000382:microbiology*; D011994:Recombinant Proteins; D057057:Serine Proteases / Q000235:genetics / Q000502:physiology*; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013296:Streptococcus pneumoniae / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D053719:Tandem Mass Spectrometry
chemical_list: D001059:Apoproteins; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; C039223:apolactoferrin; D057057:Serine Proteases; D007781:Lactoferrin