INVESTIGADORES
VENTURA Alejandra Cristina
artículos
Título:
Characterization of the reconstituted UTase/UR-PII-NRII-NRI bicyclic signal transduction system that controls the transcription of nitrogen-regulated (Ntr) genes in Escherichia coli.
Autor/es:
PENG JIANG; ALEJANDRA C VENTURA; ALEXANDER J NINFA
Revista:
BIOCHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: Washington; Año: 2012 vol. 51 p. 9045 - 9047
ISSN:
0006-2960
Resumen:
A reconstituted UTase/UR-PII-NRII-NRI bicyclic cascade regulated PII
uridylylation and NRI phosphorylation in response to glutamine. We
examined the sensitivity and robustness of the responses of the
individual cycles and of the bicyclic system. The sensitivity of the
glutamine response of the upstream UTase/UR-PII monocycle depended upon
the PII concentration, and we show that PII exerted substrate inhibition
of the UTase activity of UTase/UR, potentially contributing to this
dependence of sensitivity on PII. In the downstream NRII-NRI monocycle,
PII controlled NRI phosphorylation state, and the response to PII was
hyperbolic at both saturating and unsaturating NRI concentration. As
expected from theory, the level of NRI∼P produced by the NRII-NRI
monocycle was robust to changes in the NRII or NRI concentrations when
NRI was in excess over NRII, as long as the NRII concentration was above
a threshold value, an example of absolute concentration robustness
(ACR). Because of the parameters of the system, at physiological protein
levels and ratios of NRI to NRII, the level of NRI∼P depended upon both
protein concentrations. In bicyclic UTase/UR-PII-NRII-NRI systems, the
NRI phosphorylation state response to glutamine was always hyperbolic,
regardless of the PII concentration or sensitivity of the upstream
UTase/UR-PII cycle. In these bicyclic systems, NRI phosphorylation state
was only robust to variation in the PII/NRII ratio within a narrow
range; when PII was in excess NRI∼P was low, and when NRII was in excess
NRI phosphorylation was elevated, throughout the physiological range of
glutamine concentrations. Our results show that the bicyclic system
produced a graded response of NRI phosphorylation to glutamine under a
range of conditions, and that under most conditions the response of NRI
phosphorylation state to glutamine levels depended on the concentrations
of NRI, NRII, and PII.