FIGURE 5.

Structural changes of α1 and α2 in CagL in response to pH. A, superposition of all four CagL structures; CagL^4x5u, pH 4.5 (red); CagL^4cii, pH 4.2 (cyan); CagL^3zci, pH 7.4 (green); and CagL^3zcj, pH 6.5 (orange). B, lowering of the pH (CagL^4x5u and CagL^3zcj) causes a registry shift of α1 (CagL^3zci) as monitored by Asp⁴⁶ moving up by one turn of the helix. C, movement of α1 causes the N-terminal half of α2 below the RGD motif to move. With α1 in the up position (CagL^4x5u and CagL^3zcj), α2 is not kinked and remains straight. When α1 is in the down position or missing (CagL^4cii and CagL^3zci), α2 becomes kinked. Glu⁶² shows the degree of movement of α2. D, conformational changes in α1 and α2 result in small differences in the RGD motif in α2. In CagL^4x5u, Arg⁷⁶ forms a salt bridge to α1, whereas in the other structures, Arg⁷⁶ is either free or the backbone is in a distorted conformation.