Involved in the biosynthesis of the macrolide antibiotics methymycin, neomethymycin, narbomycin, and pikromycin. Catalyzes the attachment of dTDP-D-desosamine onto 12- and 14-membered macrolactone rings 10-deoxymethynolide and narbonolide to produce 10-deoxymethymycin (YC-17) and narbomycin. DesVII is unique among glycosyltransferases in that it requires an additional protein component, DesVIII, for its activity. DesVII can recognize and process not only cyclic substrates of different ring size, but also a variety of linear substrates albeit with reduced, but measurable activities (PubMed:18548476). Both L-sugars and D-sugars are recognized as substrates and variant substitutions at C-3 and C-4 are tolerated, but deoxygenation at C-6 is required (PubMed:16538696). 10-deoxymethynolide + dTDP-alpha-D-desosamine = 10-deoxymethymycin + dTDP + H(+) Antibiotic biosynthesis. Forms a complex with DesVIII. Cells lacking this gene are not able to produce glycosylated macrolides. DesVIII assists the folding of the DesVII polypeptide. However, unlike chaperones, it remains bound to DesVII during catalysis, forming a tight DesVII/DesVIII complex. Although the formation of the DesVII/DesVIII complex is essential for the catalytic activity, DesVIII is unlikely to be involved in catalysis directly. Belongs to the glycosyltransferase 28 family.