Figure 1.

(A) Galactosyltransferase activity of AtGALT29A and site-directed mutants of AtGALT29A Y144A and Y144E. Affinity-purified recombinant proteins expressed in N. benthamiana leaves were incubated with UDP-¹⁴[C]-Gal in the presence of a mixture of AGP acceptors (SP₃₂) as described previously.⁷ Relative activity (%) is compared to the activity level of AtGALT29A, which represents 100% activity. The error bar indicates standard deviation (n = 3). * indicates significant differences compared to wild type AtGALT29A (p < 0.05, Student's t-test). (B) Predicted 3D structure of AtGALT29A (green) using the crystal structure elucidated from rat α-2,6-sialyltransferase⁶ (2WNB, yellow). Y144 is located on the surface of a globular catalytic domain that is 35 Å from the predicted catalytic site (His319 of 2WNB); the substrate analog (orange) is indicated.