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. 2018 Aug 3;9:1138. doi: 10.3389/fpls.2018.01138

FIGURE 6.

FIGURE 6

Granule bound starch synthases have extra loops in the region of the reducing end of acarbose. Perspective has been exaggerated and fog applied to better represent distance from the camera. AtSSIV is shown in white, OsGBSSI in purple, CLg1GBSS in blue and CpGBSSI in green. ADP and acarbose are shown as sphere models with black carbons from chain A of CLg1GBSS. Four regions, numbered from the N-terminus to the C-terminus, contain extra loops (compared to AtSSIV) that approach the reducing end of acarbose. Loop 1 is present at the sequence level in all three GBSSs but it is disordered in the crystal structure of OsGBSSI (depicted as a pink dashed line). Loops 2 and 4 are present but shorter in the rice protein while loop 3 is extended only in the rice structure, not as a result of an extension in the sequence, but as a result of an extended conformation where the other proteins have helices. A disulfide bridge is formed between loops labeled 3 and 4 in OsGBSSI, which is shown as a dashed orange line.