D-glycero-alpha-D-manno-heptose 1-phosphate guanylyltransferase (, hddC (gene), gmhD (gene)) is an enzyme with systematic name GTP:D-glycero-alpha-D-manno-heptose 1-phosphate guanylyltransferase. This enzyme catalyses the following chemical reaction
The enzyme is involved in biosynthesis of GDP-D-glycero-alpha-D-manno-heptose.