Identification of three proteins up-regulated by raw starch in Cytophaga sp.

Raw starch-digesting amylases (RSDAs) in many microorganisms convert starch granules into maltodextrins and simple sugars. We cloned and sequenced from Cytophaga sp. an RSDA with an excellent raw starch digestion activity. This RSDA was highly inducible by raw starch, but not by other sugars, suggesting that an unknown signal transduction mechanism is involved in the degradation of raw starch. We used a proteomic approach to investigate the effect of raw starch on protein expression in Cytophaga sp. Using MALDI-TOF MS protein analysis, we have identified three proteins up-regulated by raw starch, i.e., a 60-kDa chaperonin (cpn60), glutaminase, and pyruvate phosphate dikinase (PPDK). Subsequent time-course studies detected an increased expression of RSDA as well as the highest expression of PPDK occurring 6 h post-incubation with raw corn starch, implying that the latter enzyme may work along with RSDA on the digestion of raw starch. Finding these proteins up-regulated by raw starch may provide an insight into how Cytophaga sp. cells respond to raw starch stimulation.