Structural basis of collagen glucosyltransferase function and its serendipitous role in kojibiose synthesis

Collagen glucosyltransferases catalyze a unique type of collagen glucosylation that is critical for biological processes and disease mechanisms. However, the structural regulation of collagen glucosyltransferases remains poorly understood. Here, we report the crystal structures of a mimiviral collagen glucosyltransferase in its apo form and in complexes with uridine diphosphate (UDP) and the disaccharide product. Our findings reveal that the enzyme functions as a homodimer, stabilized by a loop from one subunit locking into a cleft on the opposite subunit. This dimerization enables UDP-glucose binding cooperativity and enzymatic activity, a property conserved in the human homolog. Further structural analyses suggest an induced fit model for UDP interaction, mediated by Lysine 222. The dimerization also forms an extended cleft flanked by two active sites, which likely facilitates collagen recognition. Unexpectedly, we discovered that the mimiviral collagen glucosyltransferase can also synthesize the prebiotic disaccharide kojibiose. An elongated pocket adjacent to the UDP-binding site allows the enzyme to use UDP-glucose as the sugar donor and glucose as the acceptor for kojibiose production. Enzymatic activity assays confirmed the enzyme's novel kojibiose synthesis activity in vitro and in vivo. These structural insights not only inform glucosyltransferase function but also open new avenues for biomedicine.