Recombinant Scl (rScl) proteins used in ELISA were expressed in Escherichia coli and purified by affinity chromatography using the Strep-tag selleck inhibitor II system (IBA-GmbH, Goettingen, Germany) as described previously (Xu et al., 2002; Han et al., 2006b). Briefly, the DNA fragments of several scl1 and scl2 alleles, encoding the extracellular portions of the Scl1 and Scl2 proteins, were amplified by PCR with Deep Vent Taq Polymerase (New England Biolabs, Beverly, MA) and cloned into the pASK-IBA2 vector designed for periplasmic expression. rScl proteins (0.5 μM) were immobilized onto Strep-Tactin-coated microplate wells for 1.5 h at

room temperature. Following overnight blocking with Tris-buffered saline (TBS) supplemented with 1% bovine serum albumin (BSA) at 4 °C, 1 μg of

each ligand that included plasma fibronectin (pFn), cellular fibronectin (cFn), laminin (Lm), bovine collagen types I and IV, decorin, heparin, and fibrinogen (all proteins were purchased from Sigma) was added to triplicate wells and the mixture was incubated at room temperature for 1 h. rScl-bound ligands were detected with specific primary LY2157299 price antibodies and appropriate secondary antibodies conjugated to horseradish peroxidase (HRP). The HRP reaction was developed with 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) substrate and recorded at OD415 nm after 15 min of color development. In the ligand competition experiments, purified cFn and Lm were used in a molar ratio 1 : 1. First, the primary ligands, for example cFn or Lm, were added to triplicate wells immobilized with P176 and incubated for 1 h at room temperature.

Following washes with TBS, secondary ligands were added to the appropriate wells, for example Lm was added to wells containing the Scl1–cFn complex and vice versa; samples were incubated for 1 h at room temperature. Subsequently, the ELISA proceeded as described above. To generate green fluorescent protein (GFP)-expressing GAS cells, the wild-type Sulfite dehydrogenase strain, the scl1-inactivated mutant, and mutant complemented in trans for Scl1.41-protein expression (plasmid pSL230) (Caswell et al., 2007) were transformed with the plasmid pSB027 (Cramer et al., 2003). Glass cover slips were placed in the wells of 24-well tissue culture plates and coated with 2.5 μg of purified ECM proteins or BSA overnight at 4 °C, and subsequently blocked with 1% BSA in TBS for 1 h. Approximately 1 × 107 CFU of fluorescent GAS cells were added to each well for 1 h at room temperature and unbound cells were removed by washing with PBS. ECM-bound GAS cells were fixed with 3% paraformaldehyde in PBS for 30 min. The cover slips were removed from the wells, air-dried, placed on microscope slides, and viewed by fluorescent microscopy using a 450–490 nm excitation channel at × 400 and × 1000 magnification. For quantification, GAS cells were counted in 10 random fields under × 1000 magnification.