MOLECULAR ENGINEERING OF SOLUBLE BACTERIAL PROTEINS WITH CHROMATE REDUCTASE ACTIVITY

摘要

Cr(VI) (chromate), which is a serious environmental pollutant, is amenable to bacterial bioremediation. Molecular and genetic engineering can enhance this capacity. Such approaches can, for example, decrease the sensitivity of these enzymes to other toxic waste present in chromate-contaminated sites; increase their substrate affinity and V_(max); and broaden their substrate range, enabling an individual enzyme to remediate multiple pollutants. To initiate such improvements, it is necessary to learn more about the properties and biological role of the wild type enzymes. We have cloned six bacterial genes, which fall into two homology classes, and have studied, using pure proteins, the kinetics of reduction of chromate and other compounds. All can reduce quinone; the three class Ⅰ and two of the three class Ⅱ proteins can also reduce chromate; and all the class Ⅱ, but not class Ⅰ proteins can in addition reduce nitrocompounds, which are also serious environmental pollutants. The K_m of class Ⅱ enzymes for chromate reduction is lower than that of Class Ⅰ. Our ongoing studies indicate that the biological role of these proteins may be to prevent channeling of reducing equivalents into reactive oxygen species-generating pathways. Thus, strengthening the activity of these gene products may also bolster cell survival.