Involved in the catabolism of D-glucosaminate. Catalyzes the conversion of D-glucosaminate 6-phosphate to yield keto-3-deoxygluconate 6-phosphate (KDGP). 2-amino-2-deoxy-D-gluconate 6-phosphate = 2-dehydro-3-deoxy-6-phospho-D-gluconate + NH4(+) By D-glucosaminate and DgaR. Belongs to the SelA family.