Figure 4.

Mutations in Asp1 and Asp3 affect secretion of adhesin from S. gordonii cells. A, ribbon diagram of the Asp1/3 complex (Asp1 in green and Asp3 in blue), with mutated Asp1 residues in the cleft between R-folds I and II shown in stick presentation in magenta. B, endogenous Asp1 protein of S. gordonii was replaced with the indicated Asp1 mutants. Secretion of FLAG-tagged GspB-F from the cells was tested by subjecting the medium and protoplasts to SDS-PAGE, followed by immunoblotting with FLAG antibodies. C, as in A, but with mutated Asp3 residues. Mutations in the potential carbohydrate-binding regions, the concave surface of the β-sandwich, and at the tips of the β-strands are shown in stick presentation in yellow and orange, respectively. D, as in B, but with an S. gordonii strain lacking Asp3, expressing either wild type or mutant Asp3. Asp3_Mu4 containing mutations E57K, K132E, K99E, Q134R, and Asp3_Mu15 harbors the mutations E45K and N46K.