Characterization of PauB, a Novel Broad-Spectrum Plasminogen Activator from Streptococcus uberis

Abstract

A bovine plasminogen activator of atypical molecular mass (ϳ45 kDa) from Streptococcus uberis strain SK880 had been identified previously (L. B. Johnsen, K. Poulsen, M. Kilian, and T. E. Petersen. Infect. Immun. 67:1072-1078, 1999). The strain was isolated from a clinical case of bovine mastitis. The isolate was found not to secrete PauA, a bovine plasminogen activator expressed by the majority of S. uberis strains. Analysis of the locus normally occupied by pauA revealed an absence of the pauA open reading frame. However, an alternative open reading frame was identified within the same locus. Sequence analysis of the putative gene suggested limited but significant homology to other plasminogen activators. A candidate signal peptide sequence and cleavage site were also identified. Expression cloning of DNA encoding the predicted mature protein (lacking signal peptide) confirmed that the open reading frame encoded a plasminogen activator of the expected size, which we have named PauB. Both native and recombinant forms of PauB displayed an unexpectedly broad specificity profile for bovine, ovine, equine, caprine, porcine, rabbit, and human plasminogen. Clinical and nonclinical field isolates from nine United Kingdom sites were screened for the pauB gene and none were identified as carrying it. Similarly, clinical isolates from 20 Danish herds were all found to encode PauA and not PauB. Therefore, PauB represents a novel but rare bacterial plasminogen activator which displays very broad specificity.Mammalian plasminogen activator and plasmin systems play a key role in numerous biological processes including fibrinolysis, degradation of extracellular matrix proteins, cellular migration, and cancer metastasis. Conversion of the plasma zymogen plasminogen to the serine protease plasmin represents the end point of a cascade of reactions culminating in fibrinolytic dissolution of blood clots (3). Plasmin also plays a role in tissue remodeling through its ability to hydrolyze extracellular matrix proteins (34) and can also initiate activation of further metalloproteinases (11). By commandeering elements of this system, a wide range of bacteria are able to bind plasmin(ogen) and thereby augment their pathogenesis over less able competitors (23). A smaller subset of bacterial species that are able to bind plasmin(ogen) also produce potent plasminogen activators. Staphylokinase (SAK), a 15.5-kDa protein secreted by Staphylococcus aureus, forms a complex in association with either fibrin-bound human plasmin or free plasmin in preference to plasminogen (reviewed recently in reference 9). The SAK-plasmin complex can in turn activate other plasminogen molecules to plasmin. Streptokinase (SK), a 47-kDa protein, was the first streptococcal plasminogen activator described for which a mechanism of action was determined (24). In contrast to SAK, SK can associate with either human plasminogen or plasmin to form an activator complex which can then interact with further plasminogen molecules to generate plasmin (29).Once activated, pla...

Virulence-associated genes and molecular typing of Streptococcus uberisassociated with bovine mastitis in northern Thailand

“…Various virulence factors such as hyaluronic acid capsules (HasA, HasB, HasC) (9), plasminogen activator proteins (PauA and PauB) (10,11) and streptokinase (12), lactoferrin binding proteins (Lbp) (13), adhesion protein (SUAM) (14), CAMP factor (15), a surface dehydrogenase protein (GapC) (16), protein involved in the active transport of solutes essential for growth in milk (OppF) (17), and a lipoprotein receptor antigen responsible for acquisition of manganese during growth in milk (MtuA) (18) have been suggested to be associated with pathogenesis of IMI caused by S. uberis. The objective of the current study was to investigate genotypic variations and distribution of virulence-associated genes of S. uberis isolated from milk samples in northern Thailand.…”

First Insights into the Evolution of Streptococcus uberis : a Multilocus Sequence Typing Scheme That Enables Investigation of Its Population Biology

“…The observation that pauA, encoding a secreted plasminogen activator, was undergoing positive selection in itself renders this scheme unsuitable for the analysis of population structure and evolutionary relationships (38). Furthermore, it has been noted that in some isolates pauA may be absent or replaced by pauB, which encodes an alternate but unrelated plasminogen activator (35).…”

Bovine Mastitis Caused By Streptococcus uberis: Virulence Factors and Biofilm

“…A second plasminogen activator called PauB, with a molecular weight of 45 kDa, was identified by Johnsen et al (1999) in a S. uberis strain isolated from a case of clinical mastitis in Denmark [44]. Ward and Leigh (2002) determined the absence of the plasminogen activator PauA in this strain and found that pauB gene was present in the locus normally occupied by pauA [43]. The authors demonstrated its activity on bovine, ovine, equine, goat, porcine, rabbit and human plasminogen.…”

“…Briefly, virulence factors includes: plasminogen activator proteins such as PauA and PauB and SK, resistance to phagocytosis presented by a hyaluronic acid capsule, CAMP factor, a surface dehydrogenase protein GapC, sortases, Opp proteins implicated in dynamic transport of solutes, lactoferrin binding proteins, and adherence and invasion of epithelial cells mediated by SUAM [42][43][44][45][46][47][48][49][50][51].…”