Xylitol disturbs protein synthesis,including the expression of HSP‐70 and HSP‐60, in Streptococcus mutans

Xylitol, a natural sugar alcohol and a caries‐preventive carbohydrate sweetener, inhibits xylitol‐sensitive wild‐type Streptococcus mutans but also selects for its natural xylitol‐resistant mutants. The aim of the work was to verify the influence of xylitol on heat shock proteins HSP‐60 (GroEL‐like) and HSP‐70 (DnaK‐like) in xylitol‐sensitive and xylitol‐resistant strains. Cells from fresh isolate S. mutans 123.1 were grown at 37°C and constant pH 7.0. The cell culture was stressed by raising the temperature to 43°C or adding xylitol (4% final). Cell proteins labeled with a cocktail of ¹⁴C‐amino acids were analyzed by SDS‐PAGE and autoradiography whereas HSP‐60 and HSP‐70 were visualized using Western immunoblotting. In both xylitol‐sensitive and xylitol‐resistant strains, heat stress was associated with an increase of both HSP‐60 (63 kDa) and HSP‐70 (71 kDa) and a decrease in the intensity of a number of other protein bands compared with cells maintained at 37°C. Exposure to xylitol but not to other polyols induced a decrease of both these heat shock proteins in the xylitol‐sensitive strain but did not modify them in the xylitol‐resistant mutant. It also decreased all protein bands above 60 kDa together with a 53 kDa protein and increased the amount of 57‐, 50‐ and 40‐kDa proteins in the xylitol‐sensitive strain whereas the proteins of the xylitol‐resistant strain remained unchanged. The results suggest that xylitol is a strong metabolic inhibitor that disturbs protein synthesis and reduces the expression of HSP‐70 and HSP‐60 proteins in the wild‐type xylitol‐sensitive S. mutans but not in the xylitol‐resistant natural mutant strain.