Bacterial physiology micr430
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Note: we are switching the order of topics for Lectures 15 & 16. Bacterial Physiology (Micr430). Lecture 15 Bacterial Physiological Adaptation (Text Chapter: 18.1; 18.5; 18.7). GLOBAL CONTROL NETWORK.

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Bacterial Physiology (Micr430)

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Note: we are switching the order of

topics for Lectures 15 & 16

Bacterial Physiology (Micr430)

Lecture 15

Bacterial Physiological Adaptation

(Text Chapter: 18.1; 18.5; 18.7)


GLOBAL CONTROL NETWORK

  • A cell must coordinate many different regulatory circuits that control many aspects of cellular physiology in response to changes in the environment - global control

  • Global regulatory networks include sets of operons and regulons scattered around chromosome


Two-component systems

  • Bacteria sense and respond to changes in outside world primarily through a network of two-component signal transduction mechanisms

  • It consists of a sensor/kinase component (usually located on inner membrane) and a regulatory protein component (response regulators) located in the cytoplasm


Two-component

Regulatory system

Fig. 18.1


Two-component systems

  • Histidine kinases (HKs) have two domains, an input domain (N-terminal) and a transmitter domain (C-termina)

  • HK receives a signal at its input domain and autophosphorylates at a histidine residue in its transmitter domain

  • HK then transfers the phosphoryl group to an aspartate residue in the receiving domain of the partner response regulator


Two-component systems

  • Response regulators (RRs) also have two domains, a receiver domain (N-terminal) and an output domain (C-terminal)

  • After obtaining a phosphoryl group from HK, RR is activated and transmits the signal to its target via its output domain

  • Most of known phosphorylated RRs bind to DNA and stimulate or repress transcription of specific genes


Structures of histidine kinases

Fig. 18.2


Structures of response regulator proteins

Fig. 18.3


Two-component systems

  • The signaling pathway also includes a phosphatase that dephosphorylates the RRs, returning it to the nonstimulated state

  • The phosphatase may be the histidine kinase itself, the response regulator, or a separate protein

  • Additional proteins or enzymes may be needed for “two”-component systems that functions as carriers of phosphate – phosphotransferases

  • This phenomenon is phosphorelay


Response to Inorganic Phosphate Supply: The Pho Regulon

  • Regulon is a set of noncontiguous operons or genes controlled by a common regulator

  • Bacteria have evolved a signaling system to induce the formation of phosphate assimilation pathways when the supply of phosphate becomes limiting


Response to Inorganic Phosphate Supply: The Pho Regulon

  • Under low phosphate conditions, E. coli stimulates transcription of at least 38 genes (most of them in operons) involved in phosphate assimilation

  • PhoR is HK; PhoB is RR

  • Pho regulon is controlled by PhoR via PhoB

  • Phosphorylated PhoB activates transcription of genes in the Pho regulon


Pho signal transduction

  • Components involved are:

    • PstS, a periplasmic Pi binding protein

    • PstA, PstB and PstC, integral membrane proteins required for Pi uptake

    • PhoU

    • PhoR, detects Pi, either directly or indirectly

    • PhoB


Model for regulation of Pho regulon

Fig. 18.11


Response to Osmotic Pressure and Temperature

  • When E. coli is growing in higher osmolarity or at high temperature, the synthesis of the bacterium’s slightly smaller porin channel, OmpC, increases relative to the larger OmpF channel

  • Smaller OmpC channel is advantageous to the cell when faced with higher osmolarity pressure


Response to Osmotic Pressure and Temperature

  • EnvZ is an inner membrane histidine kinase that is proposed to be an osmotic sensor

  • EnvZ is a transmembrane protein, with N-terminal end exposed to periplasm and C-terminal end exposed to cytoplasm

  • OmpR is the response regulator


Model for regulation

of porin synthesis

Fig. 18.12


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