Phosphate Signaling Through Alternate Conformations of the PstSCAB Phosphate Transporter

• Main Author: Vuppada, Ramesh Krishna
• Format: Others
• Published: BYU ScholarsArchive 2017
• Subjects: phosphate homeostasis; two-component signal transduction; histidine kinase; ABC transporter; Microbiology
• Online Access: https://scholarsarchive.byu.edu/etd/6641; https://scholarsarchive.byu.edu/cgi/viewcontent.cgi?article=7641&context=etd

Phosphate is an essential compound for life. Escherichia coli employs a signal transduction pathway that controls the expression of genes that are required for the high-affinity acquisition of phosphate and the utilization of alternate sources of phosphorous. These genes are only expressed when environmental phosphate is limiting. The seven genes for this signaling pathway encode the two-component regulatory proteins PhoB and PhoR, as well as the high-affinity phosphate transporter PstSCAB and an auxiliary protein called PhoU. As the sensor kinase PhoR has no periplasmic sensory domain, the mechanism by which these cells sense environmental phosphate is not known. This paper explores the hypothesis that it is the alternating conformations of the PstSCAB transporter which are formed as part of the normal phosphate transport cycle that signal phosphate sufficiency or phosphate limitation. We tested two variants of PstB that are predicted to lock the protein in either of two conformations for their signaling output. We observed that the pstBQ160K mutant, predicted to reside in an inward facing, open conformation signaled phosphate sufficiency whereas the pstBE179Q mutant, predicted to reside in an outward facing, closed conformation signaled phosphate starvation. Neither mutant showed phosphate transport.