The present invention relates to improved variants of soluble pyrroloquinoline quinone (PQQ)-dependent glucose dehydrogenases (s-GDH) comprising an amino acid insertion between positions 428 and 429 as corresponding to the amino acid sequence known from Acinetobacter calcoaceticus, to genes encoding such variant s-GDH, to proteins of such s-GDH variants with improved substrate specificity for glucose, and to different applications of these s-GDH variants, particularly for determining concentrations of sugars, especially of glucose in a sample.