Figure 6.

Characterization of a new Rubisco interacting loop. A, Relative position of the Q217-containing loop in context of the Rca hexamer. A surface representation of the hexameric tobacco Rca model (PDB:3ZW6) is shown with alternate subunits colored in blue and light blue. The specificity helix H9 is colored red, and the last resolved residues flanking the flexible loop are shown in orange (T206) and yellow (E218). The close-up view shows the local secondary structure with helices represented by cylinders. The loop is indicated by a dotted line. B, Logo motif of the loop from an alignment of 220 plant Rca sequences generated using WebLogo (Crooks et al., 2004). C, Biochemical characterization of loop mutants was performed as in Figure 1C. Error bars indicate mean and sd of independent experiments with n = 4 to 9. D, The loop region in the Arabidopsis Rca structure (PDB:4W5W) suggests that the carboxyl group of E217 forms a salt-bridge with the amino group of K162. For simplicity, residue numbering in all panels of this figure corresponds to the OsRcaβ sequence. Structures were drawn using Pymol (www.pymol.org).