Expression in GBS of Bsp recombinant proteins with structurally unrelated signal peptides.


<p>(A) <i>Bam</i>HI-<i>Not</i>I PCR fragments carrying the ribosome binding site (RBS) and the signal peptides (SP) of 5 SecA-dependent substrates (Bsp, Alp2, Gbs0791, PilB, and CspA) were fused in frame with a <i>Not</i>I-<i>Pst</i>I PCR fragment coding the Bsp protein devoid of its signal peptide (<a href="" target="_blank">Table S1</a>). The resulting <i>Bam</i>HI-<i>Pst</i>I fragments were cloned downstream the constitutive P<i>tetM</i> promoter from the low-copy-number pTCV<i>-erm</i>. The SP and Bsp sequences are indicated in upper-bold italic characters and upper-bold characters, respectively. The boxed RP motif in all proteins corresponded to the translation of the two internal codons of the <i>Not</i>I restriction site (CGGCCG). All but one SP were predicted with SignalP 4.1 (<a href="" target="_blank"></a>) whereas the remaining (Alp2) was predicted with PrediSi (<a href="" target="_blank"></a>). The AA residues in the SP thought to direct localized secretion at the bacterial surface are indicated in red characters. Arrowheads indicate the predicted site of cleavage of the various SP. (B) Analysis of surface display of Bsp recombinant proteins in a Δ<i>bsp</i> mutant strain by immunoblotting. Whole bacterial cells harvested in exponential (OD<sub>600</sub> 0.3) or stationary (OD<sub>600</sub> 1.2) phases were washed, resuspended in phosphate buffer saline to similar density and spotted on nitrocellulose. Membranes were hybridized with specific anti-Bsp antibodies or with anti-GBS pAb (loading control). (C) Western blotting analysis of culture supernatants. Proteins were separated on 4–12% gradient Tris-acetate Criterion XT SDS-PAGE gel, then transferred onto a nitrocellulose membrane, and detected by immunoblotting with specific anti-Bsp and anti-CAMP antibodies. In (B) and (C), the Δ<i>bsp</i> mutant strain harboring pTCV-<i>erm</i> (negative control) or pTCV-<i>erm</i> directing synthesis of recombinant Bsp proteins associated with Alp2, Gbs0791, PilB, and CspA signal peptides were used.</p

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