Component of the tagatose-1,6-bisphosphate aldolase GatYZ that is required for full activity and stability of the Y subunit. Could have a chaperone-like function for the proper and stable folding of GatY. When expressed alone, GatZ does not show any aldolase activity. Is involved in the catabolism of galactitol. Carbohydrate metabolism; D-tagatose 6-phosphate degradation; D-glyceraldehyde 3-phosphate and glycerone phosphate from D-tagatose 6-phosphate: step 2/2. Forms a complex with GatY. By galactitol. Belongs to the GatZ/KbaZ family. GatZ subfamily.